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Brain Anatomy and How the Brain Works

What is the brain.

The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS.

What is the brain made of?

Weighing about 3 pounds in the average adult, the brain is about 60% fat. The remaining 40% is a combination of water, protein, carbohydrates and salts. The brain itself is a not a muscle. It contains blood vessels and nerves, including neurons and glial cells.

What is the gray matter and white matter?

Gray and white matter are two different regions of the central nervous system. In the brain, gray matter refers to the darker, outer portion, while white matter describes the lighter, inner section underneath. In the spinal cord, this order is reversed: The white matter is on the outside, and the gray matter sits within.

Gray matter is primarily composed of neuron somas (the round central cell bodies), and white matter is mostly made of axons (the long stems that connects neurons together) wrapped in myelin (a protective coating). The different composition of neuron parts is why the two appear as separate shades on certain scans.

Each region serves a different role. Gray matter is primarily responsible for processing and interpreting information, while white matter transmits that information to other parts of the nervous system.

How does the brain work?

The brain sends and receives chemical and electrical signals throughout the body. Different signals control different processes, and your brain interprets each. Some make you feel tired, for example, while others make you feel pain.

Some messages are kept within the brain, while others are relayed through the spine and across the body’s vast network of nerves to distant extremities. To do this, the central nervous system relies on billions of neurons (nerve cells).

Main Parts of the Brain and Their Functions

At a high level, the brain can be divided into the cerebrum, brainstem and cerebellum.

The cerebrum (front of brain) comprises gray matter (the cerebral cortex) and white matter at its center. The largest part of the brain, the cerebrum initiates and coordinates movement and regulates temperature. Other areas of the cerebrum enable speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions relate to vision, hearing, touch and other senses.

Cerebral Cortex

Cortex is Latin for “bark,” and describes the outer gray matter covering of the cerebrum. The cortex has a large surface area due to its folds, and comprises about half of the brain’s weight.

The cerebral cortex is divided into two halves, or hemispheres. It is covered with ridges (gyri) and folds (sulci). The two halves join at a large, deep sulcus (the interhemispheric fissure, AKA the medial longitudinal fissure) that runs from the front of the head to the back. The right hemisphere controls the left side of the body, and the left half controls the right side of the body. The two halves communicate with one another through a large, C-shaped structure of white matter and nerve pathways called the corpus callosum. The corpus callosum is in the center of the cerebrum.

The brainstem (middle of brain) connects the cerebrum with the spinal cord. The brainstem includes the midbrain, the pons and the medulla.

• Midbrain. The midbrain (or mesencephalon) is a very complex structure with a range of different neuron clusters (nuclei and colliculi), neural pathways and other structures. These features facilitate various functions, from hearing and movement to calculating responses and environmental changes. The midbrain also contains the substantia nigra, an area affected by Parkinson’s disease that is rich in dopamine neurons and part of the basal ganglia, which enables movement and coordination.
• Pons. The pons is the origin for four of the 12 cranial nerves, which enable a range of activities such as tear production, chewing, blinking, focusing vision, balance, hearing and facial expression. Named for the Latin word for “bridge,” the pons is the connection between the midbrain and the medulla.
• Medulla. At the bottom of the brainstem, the medulla is where the brain meets the spinal cord. The medulla is essential to survival. Functions of the medulla regulate many bodily activities, including heart rhythm, breathing, blood flow, and oxygen and carbon dioxide levels. The medulla produces reflexive activities such as sneezing, vomiting, coughing and swallowing.

The spinal cord extends from the bottom of the medulla and through a large opening in the bottom of the skull. Supported by the vertebrae, the spinal cord carries messages to and from the brain and the rest of the body.

The cerebellum (“little brain”) is a fist-sized portion of the brain located at the back of the head, below the temporal and occipital lobes and above the brainstem. Like the cerebral cortex, it has two hemispheres. The outer portion contains neurons, and the inner area communicates with the cerebral cortex. Its function is to coordinate voluntary muscle movements and to maintain posture, balance and equilibrium. New studies are exploring the cerebellum’s roles in thought, emotions and social behavior, as well as its possible involvement in addiction, autism and schizophrenia.

Brain Coverings: Meninges

Three layers of protective covering called meninges surround the brain and the spinal cord.

• The outermost layer, the dura mater , is thick and tough. It includes two layers: The periosteal layer of the dura mater lines the inner dome of the skull (cranium) and the meningeal layer is below that. Spaces between the layers allow for the passage of veins and arteries that supply blood flow to the brain.
• The arachnoid mater is a thin, weblike layer of connective tissue that does not contain nerves or blood vessels. Below the arachnoid mater is the cerebrospinal fluid, or CSF. This fluid cushions the entire central nervous system (brain and spinal cord) and continually circulates around these structures to remove impurities.
• The pia mater is a thin membrane that hugs the surface of the brain and follows its contours. The pia mater is rich with veins and arteries.

Lobes of the Brain and What They Control

Each brain hemisphere (parts of the cerebrum) has four sections, called lobes: frontal, parietal, temporal and occipital. Each lobe controls specific functions.

• Frontal lobe. The largest lobe of the brain, located in the front of the head, the frontal lobe is involved in personality characteristics, decision-making and movement. Recognition of smell usually involves parts of the frontal lobe. The frontal lobe contains Broca’s area, which is associated with speech ability.
• Parietal lobe. The middle part of the brain, the parietal lobe helps a person identify objects and understand spatial relationships (where one’s body is compared with objects around the person). The parietal lobe is also involved in interpreting pain and touch in the body. The parietal lobe houses Wernicke’s area, which helps the brain understand spoken language.
• Occipital lobe. The occipital lobe is the back part of the brain that is involved with vision.
• Temporal lobe. The sides of the brain, temporal lobes are involved in short-term memory, speech, musical rhythm and some degree of smell recognition.

Deeper Structures Within the Brain

Pituitary gland.

Sometimes called the “master gland,” the pituitary gland is a pea-sized structure found deep in the brain behind the bridge of the nose. The pituitary gland governs the function of other glands in the body, regulating the flow of hormones from the thyroid, adrenals, ovaries and testicles. It receives chemical signals from the hypothalamus through its stalk and blood supply.

Hypothalamus

The hypothalamus is located above the pituitary gland and sends it chemical messages that control its function. It regulates body temperature, synchronizes sleep patterns, controls hunger and thirst and also plays a role in some aspects of memory and emotion.

Small, almond-shaped structures, an amygdala is located under each half (hemisphere) of the brain. Included in the limbic system, the amygdalae regulate emotion and memory and are associated with the brain’s reward system, stress, and the “fight or flight” response when someone perceives a threat.

Hippocampus

A curved seahorse-shaped organ on the underside of each temporal lobe, the hippocampus is part of a larger structure called the hippocampal formation. It supports memory, learning, navigation and perception of space. It receives information from the cerebral cortex and may play a role in Alzheimer’s disease.

Pineal Gland

The pineal gland is located deep in the brain and attached by a stalk to the top of the third ventricle. The pineal gland responds to light and dark and secretes melatonin, which regulates circadian rhythms and the sleep-wake cycle.

Ventricles and Cerebrospinal Fluid

Deep in the brain are four open areas with passageways between them. They also open into the central spinal canal and the area beneath arachnoid layer of the meninges.

The ventricles manufacture cerebrospinal fluid , or CSF, a watery fluid that circulates in and around the ventricles and the spinal cord, and between the meninges. CSF surrounds and cushions the spinal cord and brain, washes out waste and impurities, and delivers nutrients.

Blood Supply to the Brain

Two sets of blood vessels supply blood and oxygen to the brain: the vertebral arteries and the carotid arteries.

The external carotid arteries extend up the sides of your neck, and are where you can feel your pulse when you touch the area with your fingertips. The internal carotid arteries branch into the skull and circulate blood to the front part of the brain.

The vertebral arteries follow the spinal column into the skull, where they join together at the brainstem and form the basilar artery , which supplies blood to the rear portions of the brain.

The circle of Willis , a loop of blood vessels near the bottom of the brain that connects major arteries, circulates blood from the front of the brain to the back and helps the arterial systems communicate with one another.

Cranial Nerves

Inside the cranium (the dome of the skull), there are 12 nerves, called cranial nerves:

• Cranial nerve 1: The first is the olfactory nerve, which allows for your sense of smell.
• Cranial nerve 2: The optic nerve governs eyesight.
• Cranial nerve 3: The oculomotor nerve controls pupil response and other motions of the eye, and branches out from the area in the brainstem where the midbrain meets the pons.
• Cranial nerve 4: The trochlear nerve controls muscles in the eye. It emerges from the back of the midbrain part of the brainstem.
• Cranial nerve 5: The trigeminal nerve is the largest and most complex of the cranial nerves, with both sensory and motor function. It originates from the pons and conveys sensation from the scalp, teeth, jaw, sinuses, parts of the mouth and face to the brain, allows the function of chewing muscles, and much more.
• Cranial nerve 6: The abducens nerve innervates some of the muscles in the eye.
• Cranial nerve 7: The facial nerve supports face movement, taste, glandular and other functions.
• Cranial nerve 8: The vestibulocochlear nerve facilitates balance and hearing.
• Cranial nerve 9: The glossopharyngeal nerve allows taste, ear and throat movement, and has many more functions.
• Cranial nerve 10: The vagus nerve allows sensation around the ear and the digestive system and controls motor activity in the heart, throat and digestive system.
• Cranial nerve 11: The accessory nerve innervates specific muscles in the head, neck and shoulder.
• Cranial nerve 12: The hypoglossal nerve supplies motor activity to the tongue.

The first two nerves originate in the cerebrum, and the remaining 10 cranial nerves emerge from the brainstem, which has three parts: the midbrain, the pons and the medulla.

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Brain Basics: Know Your Brain

The brain is the most complex part of the human body. This three-pound organ is the seat of intelligence, interpreter of the senses, initiator of body movement, and controller of behavior. Lying in its bony shell and washed by protective fluid, the brain is the source of all the qualities that define our humanity. It is the crown jewel of the human body.

This fact sheet is a basic introduction to the human brain. It can help you understand how the healthy brain works, how to keep your brain healthy, and what happens when the brain doesn't work like it should.

The Structure of the Brain

The brain is like a group of experts. All the parts of the brain work together, but each part has its own special responsibilities. The brain can be divided into three basic units: the forebrain , the midbrain , and the hindbrain .

The hindbrain includes the upper part of the spinal cord, the brain stem, and a wrinkled ball of tissue called the cerebellum . The hindbrain controls the body’s vital functions such as respiration and heart rate.

The cerebellum coordinates movement and is involved in learned movements. When you play the piano or hit a tennis ball, you are activating the cerebellum.

The uppermost part of the brainstem is the midbrain, which controls some reflex actions and is part of the circuit involved in the control of eye movements and other voluntary movements. The forebrain is the largest and most highly developed part of the human brain: it consists primarily of the  cerebrum and the structures hidden beneath it ( see " The Inner Brain").

When people see pictures of the brain it is usually the cerebrum that they notice. The cerebrum sits at the topmost part of the brain and is the source of conscious thoughts and actions. It holds your memories and allows you to plan, imagine, and think. It allows you to recognize friends, read, and play games.

The cerebrum is split into two halves (hemispheres) by a deep fissure. The two cerebral hemispheres communicate with each other through a thick tract of nerve fibers that lies at the base of this fissure, called the corpus callosum. Although the two hemispheres seem to be mirror images of each other, they are different. For instance, the ability to form words seems to lie primarily in the left hemisphere, while the right hemisphere seems to control many abstract reasoning skills.

For some as-yet-unknown reason, nearly all of the signals from the brain to the body and vice versa cross over on their way to and from the brain. This means that the right cerebral hemisphere primarily controls the left side of the body, and the left hemisphere primarily controls the right side. When one side of the brain is damaged, the opposite side of the body is affected. For example, a stroke in the right hemisphere of the brain can leave the left arm and leg paralyzed.

The Cerebral Cortex

Coating the surface of the cerebrum and the cerebellum is a vital layer of tissue the thickness of a stack of two or three dimes. It is called the cortex, from the Latin word for bark. Most of the actual information processing in the brain takes place in the cerebral cortex. When people talk about "gray matter" in the brain, they are talking about the cortex. The cortex is gray because nerves in this area lack the insulation that makes most other parts of the brain appear to be white. The folds in the brain add to its surface area and therefore increase the amount of gray matter and the volume of information that can be processed.

The Geography of Thought

Each cerebral hemisphere can be divided into sections, or lobes, each of which specializes in different functions. To understand each lobe and its specialty, we will take a tour of the cerebral hemispheres.

Frontal lobes

The two  frontal lobes lie directly behind the forehead. When you plan a schedule, imagine the future, or use reasoned arguments, these two lobes do much of the work. One of the ways the frontal lobes seem to do these things is by acting as short-term storage sites, allowing one idea to be kept in mind while other ideas are considered.

Motor cortex

In the back portion of each frontal lobe is a  motor cortex , which helps plan, control, and execute voluntary movement, like moving your arm or kicking a ball.

Parietal lobes

When you enjoy a good meal—the taste, smell, and texture of the food—two sections behind the frontal lobes called the  parietal lobes are at work. The parietal lobes also support reading and arithmetic.

Somatosensory cortex

The forward parts of these lobes, just behind the motor areas, is the somatosensory cortex . These areas receive information about temperature, taste, touch, and movement from the rest of the body.

Occipital lobes

As you look at the words and pictures on this page, two areas at the back of the brain are at work. These lobes, called the  occipital lobes , process images from the eyes and link that information with images stored in memory. Damage to the occipital lobes can cause blindness.

Temporal lobes

The last lobes on our tour of the cerebral hemispheres are the  temporal lobes , which lie in front of the visual areas and nest under the parietal and frontal lobes. Whether you appreciate symphonies or rock music, your brain responds through the activity of these lobes. At the top of each temporal lobe is an area responsible for receiving information from the ears. The underside of each temporal lobe plays a crucial role in forming and retrieving memories, including those associated with music. Other parts of this lobe integrate memories and sensations of taste, sound, sight, and touch.

The Inner Brain

Deep within the brain, hidden from view, lie structures that are the gatekeepers between the spinal cord and the cerebral hemispheres. These structures not only determine our emotional state, but they also modify our perceptions and responses and allow us to initiate movements that without thinking about them. Like the lobes in the cerebral hemispheres, the structures described below come in pairs: each is duplicated in the opposite half of the brain.

The  hypothalamus , about the size of a pearl, directs a multitude of important functions. It wakes you up in the morning and gets the adrenaline flowing during a test or job interview. The hypothalamus is also an important emotional center, controlling the chemicals that make you feel exhilarated, angry, or unhappy. Near the hypothalamus lies the  thalamus , a major clearinghouse for information going to and from the spinal cord and the cerebrum.

An arching tract of nerve cells leads from the hypothalamus and the thalamus to the  hippocampus . This tiny nub acts as a memory indexer—sending memories out to the appropriate part of the cerebral hemisphere for long-term storage and retrieving them when necessary. The  basal ganglia  (not shown) are clusters of nerve cells surrounding the thalamus. They are responsible for initiating and integrating movements. Parkinson’s disease, which results in tremors, rigidity, and a stiff, shuffling walk, affects the nerve cells in the basal ganglia.

The brain and the rest of the nervous system are composed of many different types of cells, but the primary functional unit is a cell called the neuron. All sensations, movements, thoughts, memories, and feelings are the result of signals that pass through neurons. Neurons consist of three parts: the cell body , dendrites , and the axon .

The cell body contains the nucleus, where most of the molecules that the neuron needs to survive and function are manufactured. Dendrites extend out from the cell body like the branches of a tree and receive messages from other nerve cells. Signals then pass from the dendrites through the cell body and travel away from the cell body down an axon to another neuron, a muscle cell, or cells in some other organ.

The neuron is usually surrounded by many support cells. Some types of cells wrap around the axon to form an insulating  myelin sheath . Myelin is a fatty molecule which provides insulation for the axon and helps nerve signals travel faster and farther. Axons may be very short, such as those that carry signals from one cell in the cortex to another cell less than a hair’s width away. Other axons may be very long, such as those that carry messages from the brain all the way down the spinal cord.

The Synapse

Scientists have learned a great deal about neurons by studying the synapse—the place where a signal passes from the neuron to another cell. When the signal reaches the end of the axon it stimulates the release of tiny sacs called  vesicles. These vesicles release chemicals known as  neurotransmitters  into the  synaptic cleft. The neurotransmitters cross the synapse and attach to  receptors on the neighboring cell. These receptors can change the properties of the receiving cell. If the receiving cell is also a neuron, the signal can continue the transmission to the next cell.

Some Key Neurotransmitters At Work

Neurotransmitters are chemicals that brain cells use to talk to each other. Some neurotransmitters make cells more active (called  excitatory ) while others block or dampen a cell's activity (called  inhibitory ).

• Acetylcholine is an excitatory neurotransmitter. It governs muscle contractions and causes glands to secrete hormones. Alzheimer’s disease , which initially affects memory formation, is associated with a shortage of acetylcholine.
• Glutamate is a major excitatory neurotransmitter. Too much glutamate can kill or damage neurons and has been linked to disorders including Parkinson's disease , stroke , seizures, and increased sensitivity to pain .
• GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter that helps control muscle activity and is an important part of the visual system. Drugs that increase GABA levels in the brain are used to treat epileptic seizures and tremors in patients with Huntington’s disease .
• Serotonin is a neurotransmitter that constricts blood vessels and brings on sleep. It is also involved in temperature regulation. Low levels of serotonin may cause sleep problems and depression, while too much serotonin can lead to seizures.
• Dopamine  can be excitatory or inhibitory and is involved in mood and the control of complex movements. The loss of dopamine activity in some portions of the brain leads to the muscular rigidity of Parkinson’s disease . Many medications used to treat mental health disorders and conditions work by modifying the action of dopamine in the brain.

Neurological Disorders

The brain is one of the hardest working organs in the body. When the brain is healthy it functions quickly and automatically. But when problems occur, the results can be devastating. NINDS supports research on hundreds of neurological disorders. Knowing more about the brain can lead to the development of new treatments for diseases and disorders of the nervous system and improve many areas of human health.

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The Human Brain: Anatomy and Function

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The brain directs our body’s internal functions. It also integrates sensory impulses and information to form perceptions, thoughts, and memories. The brain gives us self-awareness and the ability to speak and move in the world. Its four major regions make this possible: The cerebrum , with its cerebral cortex, gives us conscious control of our actions. The diencephalon mediates sensations, manages emotions, and commands whole internal systems. The cerebellum adjusts body movements, speech coordination, and balance, while the brain stem relays signals from the spinal cord and directs basic internal functions and reflexes.

1. The Seat of Consciousness: High Intellectual Functions Occur in the Cerebrum

The cerebrum is the largest brain structure and part of the forebrain (or prosencephalon). Its prominent outer portion, the cerebral cortex, not only processes sensory and motor information but enables consciousness, our ability to consider ourselves and the outside world. It is what most people think of when they hear the term “grey matter.” The cortex tissue consists mainly of neuron cell bodies, and its folds and fissures (known as gyri and sulci) give the cerebrum its trademark rumpled surface. The cerebral cortex has a left and a right hemisphere. Each hemisphere can be divided into four lobes: the frontal lobe, temporal lobe, occipital lobe, and parietal lobe. The lobes are functional segments. They specialize in various areas of thought and memory, of planning and decision making, and of speech and sense perception.

2. The Cerebellum Fine-Tunes Body Movements and Maintains Balance

The cerebellum is the second largest part of the brain. It sits below the posterior (occipital) lobes of the cerebrum and behind the brain stem, as part of the hindbrain. Like the cerebrum, the cerebellum has left and right hemispheres. A middle region, the vermis, connects them. Within the interior tissue rises a central white stem, called the arbor vitae because it spreads branches and sub-branches through the hemispheres. The primary function of the cerebellum is to maintain posture and balance. When we jump to the side, reach forward, or turn suddenly, it subconsciously evaluates each movement. The cerebellum then sends signals to the cerebrum, indicating muscle movements that will adjust our position to keep us steady.

3. The Brain Stem Relays Signals Between the Brain and Spinal Cord and Manages Basic Involuntary Functions

The brain stem connects the spinal cord to the higher-thinking centers of the brain. It consists of three structures: the medulla oblongata , the pons , and the midbrain . The medulla oblongata is continuous with the spinal cord and connects to the pons above. Both the medulla and the pons are considered part of the hindbrain. The midbrain, or mesencephalon, connects the pons to the diencephalon and forebrain. Besides relaying sensory and motor signals, the structures of the brain stem direct involuntary functions. The pons helps control breathing rhythms. The medulla handles respiration, digestion, and circulation, and reflexes such as swallowing, coughing, and sneezing. The midbrain contributes to motor control, vision, and hearing, as well as vision- and hearing-related reflexes.

4. A Sorting Station: The Thalamus Mediates Sensory Data and Relays Signals to the Conscious Brain

The diencephalon is a region of the forebrain, connected to both the midbrain (part of the brain stem) and the cerebrum. The thalamus forms most of the diencephalon. It consists of two symmetrical egg-shaped masses, with neurons that radiate out through the cerebral cortex. Sensory data floods into the thalamus from the brain stem, along with emotional, visceral, and other information from different areas of the brain. The thalamus relays these messages to the appropriate areas of the cerebral cortex. It determines which signals require conscious awareness, and which should be available for learning and memory.

5. The Hypothalamus Manages Sensory Impulses, Controls Emotions, and Regulates Internal Functions

The hypothalamus is part of the diencephalon, a region of the forebrain that connects to the midbrain and the cerebrum. The hypothalamus helps to process sensory impulses of smell, taste, and vision. It manages emotions such as pain and pleasure, aggression and amusement. The hypothalamus is also our visceral control center, regulating the endocrine system and internal functions that sustain the body day to day. It translates nervous system signals into activating or inhibiting hormones that it sends to the pituitary gland. These hormones can activate or inhibit the release of pituitary hormones that target specific glands and tissues in the body. Meanwhile, the hypothalamus manages the autonomic nervous system, devoted to involuntary internal functions. It signals sleep cycles and other circadian rhythms, regulates food consumption, and monitors and adjusts body chemistry and temperature.

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External Sources

An article in Science Daily on a research study about REM sleep and the pons , a part of the brain stem.

“ A Neurosurgeon’s Overview of the Brain’s Anatomy ” from the American Association of Neurological Surgeons.

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Parts of the Brain and Their Functions

The human brain is the epicenter of our nervous system and plays a pivotal role in virtually every aspect of our lives. It’s a complex, highly organized organ responsible for thoughts, feelings, actions, and interactions with the world around us. Here is a look at the intricate anatomy of the brain, its functions, and the consequences of damage to different areas.

Introduction to the Brain and Its Functions

The brain is an organ of soft nervous tissue that is protected within the skull of vertebrates. It functions as the coordinating center of sensation and intellectual and nervous activity. The brain consists of billions of neurons (nerve cells) that communicate through intricate networks. The primary functions of the brain include processing sensory information, regulating bodily functions, forming thoughts and emotions, and storing memories.

Main Parts of the Brain – Anatomy

The three main parts of the brain are the cerebrum, cerebellum, and brainstem.

1. Cerebrum

• Location: The cerebellum occupies the upper part of the cranial cavity and is the largest part of the human brain.
• Functions: It’s responsible for higher brain functions, including thought, action, emotion, and interpretation of sensory data.
• Effects of Damage: Depending on the area affected, damage leads to memory loss, impaired cognitive skills, changes in personality, and loss of motor control.

2. Cerebellum

• Location: The cerebellum is at the back of the brain, below the cerebrum.
• Functions: It coordinates voluntary movements such as posture, balance, coordination, and speech.
• Effects of Damage: Damage causes problems with balance, movement, and muscle coordination (ataxia).

3. Brainstem

• Location: The brainstem is lower extension of the brain, connecting to the spinal cord. It includes the midbrain, pons, and medulla oblongata.
• Functions: This part of the brain controls many basic life-sustaining functions, including heart rate, breathing, sleeping, and eating.
• Effects of Damage: Damage results in life-threatening conditions like breathing difficulties, heart problems, and loss of consciousness.

Lobes of the Brain

The four lobes of the brain are regions of the cerebrum:

• Location: This is the anterior or front part of the brain.
• Functions: Decision making, problem solving, control of purposeful behaviors, consciousness, and emotions.
• Location: Sits behind the frontal lobe.
• Functions: Processes sensory information it receives from the outside world, mainly relating to spatial sense and navigation (proprioception).
• Location: Below the lateral fissure, on both cerebral hemispheres.
• Functions: Mainly revolves around auditory perception and is also important for the processing of both speech and vision (reading).
• Location: At the back of the brain.
• Functions: Main center for visual processing.

Left vs. Right Brain Hemispheres

The cerebrum has two halves, called hemispheres. Each half controls functions on the opposite side of the body. So, the left hemisphere controls muscles on the right side of the body, and vice versa. But, the functions of the two hemispheres are not entirely identical:

• Left Hemisphere: It’s dominant in language and speech and plays roles in logical thinking, analysis, and accuracy. .
• Right Hemisphere: This hemisphere is more visual and intuitive and functions in creative and imaginative tasks.

The corpus callosum is a band of nerves that connect the two hemispheres and allow communication between them.

Detailed List of Parts of the Brain

While knowing the three key parts of the brain is a good start, the anatomy is quite a bit more complex. In addition to nervous tissues, the brain also contains key glands:

• Cerebrum: The cerebrum is the largest part of the brain. Divided into lobes, it coordinates thought, movement, memory, senses, speech, and temperature.
• Corpus Callosum : A broad band of nerve fibers joining the two hemispheres of the brain, facilitating interhemispheric communication.
• Cerebellum : Coordinates movement and balance and aids in eye movement.
• Pons : Controls voluntary actions, including swallowing, bladder function, facial expression, posture, and sleep.
• Medulla oblongata : Regulates involuntary actions, including breathing, heart rhythm, as well as oxygen and carbon dioxide levels.
• Limbic System : Includes the amygdala, hippocampus, and parts of the thalamus and hypothalamus.
• Amygdala: Plays a key role in emotional responses, hormonal secretions, and memory formation.
• Hippocampus: Plays a vital role in memory formation and spatial navigation.
• Thalamus : Acts as the brain’s relay station, channeling sensory and motor signals to the cerebral cortex, and regulating consciousness, sleep, and alertness.
• Basal Ganglia : A group of structures involved in processing information related to movement, emotions, and reward. Key structures include the striatum, globus pallidus, substantia nigra, and subthalamic nucleus.
• Ventral Tegmental Area (VTA) : Plays a role in the reward circuit of the brain, releasing dopamine in response to stimuli indicating a reward.
• Optic tectum : Also known as the superior colliculus, it directs eye movements.
• Substantia Nigra : Involved in motor control and contains a large concentration of dopamine-producing neurons.
• Cingulate Gyrus : Plays a role in processing emotions and behavior regulation. It also helps regulate autonomic motor function.
• Olfactory Bulb : Involved in the sense of smell and the integration of olfactory information.
• Mammillary Bodies : Plays a role in recollective memory.
• Function: Regulates emotions, memory, and arousal.

Glands in the Brain

The hypothalamus, pineal gland, and pituitary gland are the three endocrine glands within the brain:

• Hypothalamus : The hypothalamus links the nervous and endocrine systems. It contains many small nuclei. In addition to participating in eating and drinking, sleeping and waking, it regulates the endocrine system via the pituitary gland. It maintains the body’s homeostasis, regulating hunger, thirst, response to pain, levels of pleasure, sexual satisfaction, anger, and aggressive behavior.
• Pituitary Gland : Known as the “master gland,” it controls various other hormone glands in the body, such as the thyroid and adrenals, as well as regulating growth, metabolism, and reproductive processes.
• Pineal Gland : The pineal gland produces and regulates some hormones, including melatonin, which is crucial in regulating sleep patterns and circadian rhythms.

Gray Matter vs. White Matter

The brain and spinal cord consist of gray matter (substantia grisea) and white matter (substantia alba).

• White Matter: Consists mainly of axons and myelin sheaths that send signals between different brain regions and between the brain and spinal cord.
• Gray Matter: Consists of neuronal cell bodies, dendrites, and axon terminals. Gray matter processes information and directs stimuli for muscle control, sensory perception, decision making, and self-control.

Frequently Asked Questions (FAQs) About the Human Brain

• The human brain contains approximately 86 billion neurons. Additionally, it has a similar or slightly higher number of non-neuronal cells (glial cells), making the total number of cells in the brain close to 170 billion.
• There are about 86 billion neurons in the human brain. These neurons are connected by trillions of synapses, forming a complex networks.
• The average adult human brain weighs about 1.3 to 1.4 kilograms (about 3 pounds). This weight represents about 2% of the total body weight.
• The brain is about 73% water.
• The myth that humans only use 10% of their brain is false. Virtually every part gets use, and most of the brain is active all the time, even during sleep.
• The average size of the adult human brain is about 15 centimeters (6 inches) in length, 14 centimeters (5.5 inches) in width, and 9 centimeters (3.5 inches) in height.
• Brain signal speeds vary depending on the type of neuron and the nature of the signal. They travel anywhere from 1 meter per second to over 100 meters per second in the fastest neurons.
• With age, the brain’s volume and/or weight decrease, synaptic connections reduce, and there can be a decline in cognitive functions. However, the brain to continues adapting and forming new connections throughout life.
• The brain has a limited ability to repair itself. Neuroplasticity aids recovery by allowing other parts of the brain to take over functions of the damaged areas.
• The brain consumes about 20% of the body’s total energy , despite only making up about 2% of the body’s total weight . It requires a constant supply of glucose and oxygen.
• Sleep is crucial for brain health. It aids in memory consolidation, learning, brain detoxification, and the regulation of mood and cognitive functions.
• Douglas Fields, R. (2008). “White Matter Matters”. Scientific American . 298 (3): 54–61. doi: 10.1038/scientificamerican0308-54
• Kandel, Eric R.; Schwartz, James Harris; Jessell, Thomas M. (2000). Principles of Neural Science (4th ed.). New York: McGraw-Hill. ISBN 978-0-8385-7701-1.
• Kolb, B.; Whishaw, I.Q. (2003). Fundamentals of Human Neuropsychology (5th ed.). New York: Worth Publishing. ISBN 978-0-7167-5300-1.
• Rajmohan, V.; Mohandas, E. (2007). “The limbic system”. Indian Journal of Psychiatry . 49 (2): 132–139. doi: 10.4103/0019-5545.33264
• Shepherd, G.M. (1994). Neurobiology . Oxford University Press. ISBN 978-0-19-508843-4.

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Parts of the Brain

Anatomy, Functions, and Conditions

The Cerebral Cortex

The four lobes, the brain stem, the cerebellum, the limbic system, other parts of the brain, brain conditions, protecting your brain.

The human brain  is not only one of the most important organs in the human body; it is also the most complex. The brain is made up of billions of neurons and it also has a number of specialized parts that are each involved in important functions.

While there is still a great deal that researchers do not yet know about the brain, they have learned a great deal about the anatomy and function of the brain. Understanding these parts can help give people a better idea of how disease and damage may affect the brain and its ability to function.

The cerebral cortex is the part of the brain that makes human beings unique. Functions that originate in the cerebral cortex include:

• Consciousness
• Higher-order thinking
• Imagination
• Information processing
• Voluntary physical action

The cerebral cortex is what we see when we look at the brain. It is the outermost portion that can be divided into four lobes. Each bump on the surface of the brain is known as a gyrus , while each groove is known as a sulcus (gyri and sulci are the plural form).

The cerebral cortex is the largest part of the brain and is responsible for a number of complex functions, including conscious thought, information processing, language, memory, behavior, and personality.

The cerebral cortex can be divided into four sections, known as lobes. The frontal lobe, parietal lobe, occipital lobe, and temporal lobe have been associated with different functions ranging from reasoning and memory to auditory and visual perception.

Frontal Lobe

This lobe is located at the front of the brain and is associated with reasoning, motor skills, higher-level cognition, and expressive language.

• At the front of the frontal lobe is the prefrontal cortex , which is responsible for most executive functions , like thinking, paying attention, and self-control. Damage to the frontal lobe can lead to changes in sexual habits, socialization, and attention, as well as increased risk-taking .
• The motor cortex , also known as the motor homunculus  (meaning 'little person'), lies at the back of the frontal lobe, near the central sulcus. It receives information from various lobes of the brain and uses it to carry out body movements like playing the piano, blowing a kiss, and skipping.

Parietal Lobe

The parietal lobe is located in the middle section of the brain, just behind the frontal lobe. It is associated with processing tactile sensory information such as pressure, touch, and pain .

A portion of the parietal lobe known as the somatosensory cortex is located just behind the central sulcus and is essential to the processing of the body's senses. It is also known as the somatosensory homunculus .

The homunculus is known as the "little person' in the brain because it has a topographical map of the whole human body in a small area of the cerebral cortex. There is one for the motor cortex in the frontal lobe and one for the somatosensory cortex in the parietal lobe.

Temporal Lobe

The temporal lobe is located on the bottom section of the brain next to the temples and ears.

• This lobe is also the location of the primary auditory cortex , which is important for interpreting sounds, tones, and frequencies. This cortex has a topographical map of the cochlea, a tiny organ in the inner ear.
• The secondary auditory cortex contains Wernicke's area , which is responsible for understanding spoken or written human language.
• The hippocampus is also located in the temporal lobe, which is why this portion of the brain is also heavily associated with the formation of memories .

Damage to the temporal lobe can lead to problems with memory, sound discrimination, and speech comprehension.

Occipital Lobe

The occipital lobe is located at the back portion of the brain and is associated with interpreting visual stimuli and information. The primary visual cortex , which receives and interprets information from the retinas of the eyes, is located in the occipital lobe.

Damage to this lobe can cause visual problems such as difficulty recognizing objects, an inability to identify colors, and trouble recognizing words.

The brain comprises four lobes, each associated with different functions. The frontal lobe is found at the front of the brain; the parietal lobe is behind the frontal lobe; the temporal lobe is located at the sides of the head; and the occipital lobe is found at the back of the head.

The brainstem is an area located at the base of the brain that contains structures vital for involuntary functions such as heartbeat and breathing. It is comprised of the midbrain, pons, and medulla.

The midbrain is often considered the smallest region of the brain. It acts as a relay station for auditory and visual information and controls many important functions, such as the visual and auditory systems, as well as eye movement.

Portions of the midbrain called the  red nucleus  and the  substantia nigra  are involved in the control of body movement. The darkly pigmented substantia nigra contains a large number of dopamine-producing neurons.

The degeneration of neurons in the substantia nigra is associated with Parkinson’s disease.

The medulla is located directly above the spinal cord in the lower part of the brain stem and controls many vital autonomic functions such as heart rate, breathing, and blood pressure.

The pons, meaning "bridge," connects the cerebral cortex to the medulla and to the cerebellum and serves a number of essential functions. It plays a role in several autonomic processes, such as stimulating breathing and controlling sleep cycles.

The brainstem, which includes the midbrain, medulla, and pons, is responsible for involuntary processes, including breathing, heartbeat, and blood pressure.

Sometimes referred to as the ​"little brain," the cerebellum lies on top of the pons behind the brain stem. The cerebellum makes up approximately 10% of the brain's total size , but it accounts for more than 50% of the total number of neurons located in the entire brain .

The cerebellum is comprised of small lobes and serves several functions.

• It receives information from the inner ear's balance system, sensory nerves, and auditory and visual systems. It is involved in coordinating movements and motor learning.
• It helps control posture, balance, and the coordination of voluntary movements. This allows different muscle groups to act together and produce coordinated fluid movement.
• It is also important in certain cognitive functions, including speech.

The cerebellum is associated with motor movement and control, but this is not because the motor commands originate here. Instead, the cerebellum modifies these signals and makes motor movements accurate and useful.

The cerebellum is densley packed with neurons and is responsible for managing posture, balance, and the coordination of movement.

Although there is no totally agreed-upon list of the structures that make up the limbic system, four of the main regions include:

The Hypothalamus

The hypothalamus is a grouping of nuclei that lie along the base of the brain near the pituitary gland. It connects with many other regions of the brain and is responsible for controlling hunger, thirst, emotions , body temperature regulation, and circadian rhythms.

The hypothalamus also controls the pituitary gland by secreting hormones. This gives the hypothalamus a great deal of control over many body functions.

The Amygdala

The amygdala is a cluster of nuclei located close to the base of the brain. It is primarily involved in functions including memory, emotion, and the body's fight-or-flight response . The structure processes external stimuli and then relays that information to the hippocampus, which can then prompt a response to deal with outside threats.

The Thalamus

Located above the brainstem, the thalamus processes and transmits movement and sensory information . It is essentially a relay station, taking in sensory information and then passing it on to the cerebral cortex. The cerebral cortex also sends information to the thalamus, which then sends this information to other systems.

The Hippocampus

The hippocampus is a structure located in the temporal lobe. It is important in memory and learning and is considered to be part of the limbic system because it plays an important part in emotional regulation or the control of emotional responses . It plays a role in the body's fight-or-flight response and in the recall of emotional memories.

The limbic system controls behaviors essential for well-being and survival, including emotional regulation, the fight-or-flight response, feeding behavior, and reproduction.

Other important structures play an essential role in supporting the structure and function of the brain. Some of these parts of the brain include:

The meninges are the layers that surround the brain and spinal cord and provide protection. There are three layers of meninges:

• The dura mater : This is the thick, outmost layer located directly under the skull and vertebral column.
• The arachnoid mater : This is a thin layer of web-like connective tissue. Under this layer is cerebrospinal fluid that helps cushion the brain and spinal cord.
• The pia mater : This layer contains veins and arteries and is found directly atop the brain and spinal cord.

The brain also contains 12 cranial nerves. Each nerve plays a vital role in relaying essential information to the brain. These nerves include:

• The olfactory nerve : Essential for the sense of smell
• The optic nerve : Controls eyesight
• The oculomotor nerve : Controls the motions of the eye and the response of the pupil
• The trochlea nerve : Controls the muscles of the eye
• The trigeminal nerve : Carries sensory and motor information to and from the face, jaw, teeth, and scalp
• Abducens nerve : Associated with specific movements of the eye
• Facial nerve : Responsible for sensory and motor functions controlling the face, tongue, tear glands, and parts of the ear
• The vestibulocochlear nerve , which regulates hearing and balance
• The glossopharyngeal nerve : Important for sensory information from parts of the tongue and stimulating specific throat muscles
• The vagus nerve : Plays many important roles, including carrying sensory information from the ear, heart, intestines
• The accessory nerve : Controls the muscles of the neck
• The hypoglossal nerve : Responsible for the muscle movements of the tongue

In addition to the main parts of the brain, there are also other important structures that are important for normal functioning. This includes the protective meninges and the cranial nerves that transmit signals to and from the brain.

The brain can also be affected by a number of conditions and damage. According to the National Institute of Neurological Disorders and Stroke, there are more than 600 types of neurological diseases. Some conditions that can affect the brain and its function include:

• Brain tumors
• Cerebrovascular diseases such as stroke and vascular dementia
• Convulsive disorders such as epilepsy
• Degenerative diseases such as Alzheimer's disease and Parkinson's disease
• Developmental disorders such as cerebral palsy
• Infectious diseases such as AIDS dementia
• Metabolic diseases such as Gaucher's disease
• Neurogenetic diseases, including Huntington's disease and muscular dystrophy
• Trauma such as head injury and spinal cord injury

By studying the brain and learning more about its anatomy and function, researchers are able to develop new treatments and preventative strategies for conditions that affect the brain.

Disease and damage can affect the brain's ability to function. Tumors, strokes, degenerative conditions, trauma, and infectious diseases are just a few of the conditions that can damage the brain.

You can't change your genetics or some other risk factors. But it's important to take steps to help protect the health of your brain.

Diet and Exercise

Research suggests that regular physical activity is essential for brain health. Exercise can help delay brain aging and degenerative diseases such as Alzheimer's, diabetes, and multiple sclerosis. It is also associated with improvements in cognitive abilities and memory.

Similarly, a nutritious, balanced diet that includes omega-3 fatty acids, vitamins, and antioxidants is important for brain function (as well as overall health).

It's also essential to protect your brain from injury by, for example, wearing a helmet when participating in physical activities that pose a risk for collision or falls, and always wearing a seatbelt when driving or riding in a car.

Sleep can also play a pivotal role in brain health and mental well-being . Studies have found that sleep can actually play a role in the development and maintenance of some psychiatric conditions, including anxiety, depression, and bipolar disorder.

Mental Activity

Evidence also suggests that staying mentally engaged can also play an important role in protecting your brain from some degenerative conditions. Activities that may help include learning new things and staying socially active.

Final Thoughts

The human brain is remarkably complex and researchers are still discovering many of the mysteries of how the mind works. By better understanding how different parts of the brain function, you can also better appreciate how disease or injury may impact it. If you think that you are experiencing symptoms of a brain condition, talk to your doctor for further evaluation.

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Wagner MJ, Kim TH, Savall J, Schnitzer MJ, Luo L. Cerebellar granule cells encode the expectation of reward . Nature . 2017;544(7648):96-100. doi:10.1038/nature21726

Biran J, Tahor M, Wircer E, Levkowitz G. Role of developmental factors in hypothalamic function . Front Neuroanat . 2015;9:47. doi:10.3389/fnana.2015.00047

Baxter MG, Croxson PL. Facing the role of the amygdala in emotional information processing . Proc Nat Acad Sci . 2012;109(52):21180-21181. doi:10.1073/pnas.1219167110

Fama R, Sullivan EV. Thalamic structures and associated cognitive functions: Relations with age and aging . Neurosci Biobehav Rev . 2015;54:29-37. doi:10.1016/j.neubiorev.2015.03.008

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By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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brain , the mass of nerve tissue in the anterior end of an organism. The brain integrates sensory information and directs motor responses; in higher vertebrates it is also the centre of learning . The human brain weighs approximately 1.4 kg (3 pounds) and is made up of billions of cells called neurons . Junctions between neurons, known as synapses , enable electrical and chemical messages to be transmitted from one neuron to the next in the brain, a process that underlies basic sensory functions and that is critical to learning , memory and thought formation, and other cognitive activities. The brain and the spinal cord together make up the system of nerve tissue in vertebrates called the central nervous system , which controls both voluntary movements, such as those involved in walking and in speech , and involuntary movements, such as breathing and reflex actions. It also is the centre of emotion and cognition . (For more information about the human brain, see nervous system , human.)

In lower vertebrates the brain is tubular and resembles an early developmental stage of the brain in higher vertebrates. It consists of three distinct regions: the hindbrain , the midbrain , and the forebrain . Although the brain of higher vertebrates undergoes considerable modification during embryonic development, these three regions are still discernible.

The hindbrain is composed of the medulla oblongata and the pons . The medulla transmits signals between the spinal cord and the higher parts of the brain; it also controls such autonomic functions as heartbeat and respiration. The pons is partly made up of tracts connecting the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum.

The midbrain, the upper portion of which evolved from the optic lobes, is the main centre of sensory integration in fish and amphibians . It also is involved with integration in reptiles and birds . In mammals the midbrain is greatly reduced, serving primarily as a connecting link between the hindbrain and the forebrain.

Connected to the medulla, pons, and midbrain by large bundles of fibres is the cerebellum . Relatively large in humans, this “little brain” controls balance and coordination by producing smooth, coordinated movements of muscle groups.

The forebrain includes the cerebral hemispheres and, under these, the brainstem , which contains the thalamus and hypothalamus . The thalamus is the main relay centre between the medulla and the cerebrum; the hypothalamus is an important control centre for sex drive , pleasure, pain, hunger, thirst, blood pressure , body temperature, and other visceral functions. The hypothalamus produces hormones that control the secretions of the anterior pituitary gland , and it also produces oxytocin and antidiuretic hormone , which are stored in and released by the posterior pituitary gland.

The cerebrum , originally functioning as part of the olfactory lobes, is involved with the more complex functions of the human brain. In humans and other advanced vertebrates, the cerebrum has grown over the rest of the brain, forming a convoluted (wrinkled) layer of gray matter . The degree of convolution is partly dependent on the size of the body. Small mammals (e.g., lesser anteater , marmoset ) generally have smooth brains, and large mammals (e.g., whale , elephant , dolphin ) generally have highly convoluted ones.

The cerebral hemispheres are separated by a deep groove, the longitudinal cerebral fissure . At the base of this fissure lies a thick bundle of nerve fibres, called the corpus callosum , which provides a communication link between the hemispheres. The left hemisphere controls the right half of the body, and vice versa, because of a crossing of the nerve fibres in the medulla or, less commonly, in the spinal cord. Although the right and left hemispheres are mirror images of one another in many ways, there are important functional distinctions. In most people, for example, the areas that control speech are located in the left hemisphere, while areas that control spatial perceptions are located in the right hemisphere.

Two major furrows—the central sulcus and the lateral sulcus—divide each cerebral hemisphere into four sections: the frontal, parietal, temporal, and occipital lobes. The central sulcus, also known as the fissure of Rolando, also separates the cortical motor area (which is anterior to the fissure) from the cortical sensory area (which is posterior to the fissure). Starting from the top of the hemisphere, the upper regions of the motor and sensory areas control the lower parts of the body, and the lower regions of the motor and sensory areas control the upper parts of the body. Other functional areas of the cerebral hemispheres have been identified, including the visual cortex in the occipital lobe and the auditory cortex in the temporal lobe. A large amount of the primate cortex, however, is devoted to no specific motor or sensory function; this so-called association cortex is apparently involved in higher mental activities.

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Introduction: The Human Brain

By Helen Phillips

4 September 2006

A false-colour Magnetic Resonance Image (MRI) of a mid-sagittal section through the head of a normal 42 year-old woman, showing structures of the brain, spine and facial tissues

(Image: Mehau Kulyk / Science Photo Library)

The brain is the most complex organ in the human body. It produces our every thought, action , memory , feeling and experience of the world. This jelly-like mass of tissue, weighing in at around 1.4 kilograms, contains a staggering one hundred billion nerve cells, or neurons .

The complexity of the connectivity between these cells is mind-boggling. Each neuron can make contact with thousands or even tens of thousands of others, via tiny structures called synapses . Our brains form a million new connections for every second of our lives. The pattern and strength of the connections is constantly changing and no two brains are alike.

It is in these changing connections that memories are stored, habits learned and personalities shaped , by reinforcing certain patterns of brain activity, and losing others.

Grey matter

While people often speak of their “ grey matter “, the brain also contains white matter . The grey matter is the cell bodies of the neurons, while the white matter is the branching network of thread-like tendrils – called dendrites and axons – that spread out from the cell bodies to connect to other neurons.

But the brain also has another, even more numerous type of cell, called glial cells . These outnumber neurons ten times over. Once thought to be support cells, they are now known to amplify neural signals and to be as important as neurons in mental calculations. There are many different types of neuron, only one of which is unique to humans and the other great apes, the so called spindle cells .

Brain structure is shaped partly by genes , but largely by experience . Only relatively recently it was discovered that new brain cells are being born throughout our lives – a process called neurogenesis . The brain has bursts of growth and then periods of consolidation , when excess connections are pruned. The most notable bursts are in the first two or three years of life, during puberty , and also a final burst in young adulthood.

How a brain ages also depends on genes and lifestyle too. Exercising the brain and giving it the right diet can be just as important as it is for the rest of the body.

Chemical messengers

The neurons in our brains communicate in a variety of ways. Signals pass between them by the release and capture of neurotransmitter and neuromodulator chemicals, such as glutamate , dopamine , acetylcholine , noradrenalin , serotonin and endorphins .

Some neurochemicals work in the synapse , passing specific messages from release sites to collection sites, called receptors. Others also spread their influence more widely, like a radio signal , making whole brain regions more or less sensitive.

These neurochemicals are so important that deficiencies in them are linked to certain diseases. For example, a loss of dopamine in the basal ganglia, which control movements, leads to Parkinson’s disease . It can also increase susceptibility to addiction because it mediates our sensations of reward and pleasure.

Similarly, a deficiency in serotonin , used by regions involved in emotion, can be linked to depression or mood disorders, and the loss of acetylcholine in the cerebral cortex is characteristic of Alzheimer’s disease .

Brain scanning

Within individual neurons, signals are formed by electrochemical pulses. Collectively, this electrical activity can be detected outside the scalp by an electroencephalogram (EEG).

These signals have wave-like patterns , which scientists classify from alpha (common while we are relaxing or sleeping ), through to gamma (active thought). When this activity goes awry, it is called a seizure . Some researchers think that synchronising the activity in different brain regions is important in perception .

Other ways of imaging brain activity are indirect. Functional magnetic resonance imaging ( fMRI ) or positron emission tomography ( PET ) monitor blood flow. MRI scans, computed tomography ( CT ) scans and diffusion tensor images (DTI) use the magnetic signatures of different tissues, X-ray absorption, or the movement of water molecules in those tissues, to image the brain.

These scanning techniques have revealed which parts of the brain are associated with which functions . Examples include activity related to sensations , movement, libido , choices , regrets , motivations and even racism . However, some experts argue that we put too much trust in these results and that they raise privacy issues .

Before scanning techniques were common, researchers relied on patients with brain damage caused by strokes , head injuries or illnesses, to determine which brain areas are required for certain functions . This approach exposed the regions connected to emotions , dreams , memory , language and perception and to even more enigmatic events, such as religious or “ paranormal ” experiences.

One famous example was the case of Phineas Gage , a 19 th century railroad worker who lost part of the front of his brain when a 1-metre-long iron pole was blasted through his head during an explosion. He recovered physically, but was left with permanent changes to his personality , showing for the first time that specific brain regions are linked to different processes.

Structure in mind

The most obvious anatomical feature of our brains is the undulating surfac of the cerebrum – the deep clefts are known as sulci and its folds are gyri. The cerebrum is the largest part of our brain and is largely made up of the two cerebral hemispheres . It is the most evolutionarily recent brain structure, dealing with more complex cognitive brain activities.

It is often said that the right hemisphere is more creative and emotional and the left deals with logic, but the reality is more complex . Nonetheless, the sides do have some specialisations , with the left dealing with speech and language , the right with spatial and body awareness.

See our Interactive Graphic for more on brain structure

Further anatomical divisions of the cerebral hemispheres are the occipital lobe at the back, devoted to vision , and the parietal lobe above that, dealing with movement , position, orientation and calculation .

Behind the ears and temples lie the temporal lobes , dealing with sound and speech comprehension and some aspects of memory . And to the fore are the frontal and prefrontal lobes , often considered the most highly developed and most “human” of regions, dealing with the most complex thought, decision making , planning, conceptualising, attention control and working memory. They also deal with complex social emotions such as regret , morality and empathy .

Another way to classify the regions is as sensory cortex and motor cortex , controlling incoming information, and outgoing behaviour respectively.

Below the cerebral hemispheres, but still referred to as part of the forebrain, is the cingulate cortex , which deals with directing behaviour and pain . And beneath this lies the corpus callosum , which connects the two sides of the brain. Other important areas of the forebrain are the basal ganglia , responsible for movement , motivation and reward.

Urges and appetites

Beneath the forebrain lie more primitive brain regions. The limbic system , common to all mammals, deals with urges and appetites. Emotions are most closely linked with structures called the amygdala , caudate nucleus and putamen . Also in the limbic brain are the hippocampus – vital for forming new memories; the thalamus – a kind of sensory relay station; and the hypothalamus , which regulates bodily functions via hormone release from the pituitary gland .

The back of the brain has a highly convoluted and folded swelling called the cerebellum , which stores patterns of movement, habits and repeated tasks – things we can do without thinking about them.

The most primitive parts, the midbrain and brain stem , control the bodily functions we have no conscious control of, such as breathing , heart rate, blood pressure, sleep patterns , and so on. They also control signals that pass between the brain and the rest of the body, through the spinal cord.

Though we have discovered an enormous amount about the brain, huge and crucial mysteries remain. One of the most important is how does the brain produces our conscious experiences ?

The vast majority of the brain’s activity is subconscious . But our conscious thoughts, sensations and perceptions – what define us as humans – cannot yet be explained in terms of brain activity.

• psychology /

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Physiology, brain.

Kenia A. Maldonado ; Khalid Alsayouri .

Affiliations

Last Update: March 17, 2023 .

• Introduction

The human brain is perhaps the most complex of all biological systems, with the mature brain composed of more than 100 billion information-processing cells called neurons. [1]  The brain is an organ composed of nervous tissue that commands task-evoked responses, movement, senses, emotions, language, communication, thinking, and memory. The three main parts of the human brain are the cerebrum, cerebellum, and brainstem. See Image. Human Brain, Encephalon.

The cerebrum is divided into the right and left hemispheres and is the largest part of the brain. It contains folds and convolutions on its surface, with the ridges found between the convolutions called gyri and the valleys between the gyri called sulci (plural of sulcus). If the sulci are deep, they are called fissures. Both cerebral hemispheres have an outer layer of gray matter called the cerebral cortex and inner subcortical white matter.

Located in the posterior cranial fossa, above the foramen magnum, the cerebellum's primary function is to modulate motor coordination, posture, and balance. It is comprised of the cerebellar cortex and deep cerebellar nuclei, with the cerebellar cortex being made up of three layers; the molecular, Purkinje, and granular layers. The cerebellum connects to the brainstem via cerebellar peduncles.

The brainstem contains the midbrain, pons, and medulla. It is located anterior to the cerebellum, between the base of the cerebrum and the spinal cord.

• Issues of Concern

Studies of brain function have focused on analyzing the variations of the electrical activity produced by the application of sensory stimuli. However, it is also essential to study additional features and functions of the brain, including information processing and responding to environmental demands. [2]

The brain works precisely, making connections, and is a deeply divided structure that has remained not entirely explained or examined. [3]  Although researchers have made significant progress in experimental techniques, the human cognitive function that emerges from neuronal structure and dynamics is not entirely understood. [4]

• Cellular Level

At the beginning of the forebrain formation, the neuroepithelial cells undergo divisions at the inner surface of the neural tube to generate new progenitors. These dividing neuroepithelial cells transform and diversify, leading to radial glial cells (RGCs).

RGCs also work as progenitors with the capacity to regenerate themselves and produce other types of progenitors, neurons, and glial cells. [5]  RGCs have long processes that connect with the neuroepithelium and function as a guide for the migration of neuron cells to ensure that neurons find their resting place, mature, and send out axons and dendrites to participate directly in synapses and electrical signaling. Neurons get produced along with glial cells; glial cells bring support and create an enclosed environment in which neurons can perform their functions.

Glial cells (astrocytes, oligodendrocytes, microglial cells) have well-known roles, which include: keeping the ionic medium of neurons, controlling the rate of nerve signal propagation and synaptic action by regulating the uptake of neurotransmitters, providing a platform for some aspects of neural development, and aiding in recovery from neural damage.

Gray matter is the main component of the central nervous system (CNS) and consists of neuronal cell bodies, dendrites, myelinated and unmyelinated axons, glial cells, synapses, and capillaries. The cerebral cortex is made up of layers of neurons that constitute the gray matter of the brain. The subcortical (beneath the cortex) area is primarily white matter composed of myelinated axons with fewer quantities of cell bodies when compared to gray matter.

Although neurons can have different morphologies, they all contain four common regions: the cell body, the dendrites, the axon, and the axon terminals, each with its respective functions.

The cell body contains a nucleus where proteins and membranes are synthesized. These proteins travel through microtubules down to the axons and terminals via a mechanism known as anterograde transport. In retrograde transport, damaged membranes and organelles travel from the axon toward the cell body along axonal microtubules. Lysosomes are only present in the cell body and are responsible for containing and degrading damaged material. The axon is a thin continuation of a neuron that allows electrical impulses to be sent from neuron to neuron.

Astrocytes occupy 25% of the total brain volume and are the most abundant glial cells. [6]  They are classified into two main groups: protoplasmic and fibrous. Protoplasmic astrocytes appear in gray matter and have several branches that contact both synapses and blood vessels. Fibrous astrocytes are present in the white matter and have long fiber-like processes that contact the nodes of Ranvier and the blood vessels. Astrocytes use their connections to vessels to titrate blood flow in synaptic activity responses. Astrocytic endfeet, which forms tight junctions between endothelial cells and the basal lamina, gives rise to the formation of the blood-brain barrier (BBB). [7]

The primary function of oligodendrocytes is to make myelin, a proteolipid critical in maintaining electrical impulse conduction and maximizing velocity. Myelin is located in segments separated by nodes of Ranvier, and their function is equivalent to those of Schwan cells in the peripheral nervous system.

The macrophage populations of the CNS include microglia, perivascular macrophages, meningeal macrophages, macrophages of the circumventricular organs (CVO), and the microglia of the choroid plexus. Microglia are phagocytic cells representing the immune and support system of the CNS and are the most abundant cells of the choroid plexus. [8]

• Development

Human brain development starts with the neurulation process from the ectodermic layer of the embryo and takes, on average, 20 to 25 years to mature. [9]  It occurs in a sequential and organized manner, beginning with the neural tube formation at the third or fourth week of gestation. This is followed by cell migration and proliferation that leads to the folding of the cerebral cortex to increase its size and surface area, creating a more complex structure. Failure of this migration and proliferation leads to a smooth brain without sulci or gyri, termed lissencephaly. [10] At birth, the general architecture of the brain is mostly complete, and by the age of 5 years, the total brain volume is about 95% of its adult size. Generally, the white matter increases with age, while the gray matter decreases with age.

The brain's most prominent white matter structure, the corpus callosum, increases by approximately 1.8% per year between the ages of 3 and 18 years. [11]  The corpus callosum conjugates the activity of the right and left hemispheres and allows for the progress of higher-order cognitive abilities.

Gray matter in the frontal lobe undergoes continued structural development, reaching its maximal volume at 11 to 12 years of age before slowing down during adolescence and early adulthood. The gray matter in the temporal lobe follows a similar development pattern, reaching its maximum size at 16 to 17 years of age with a slight decline afterward. [12]

Below is a list of the brain vesicles and the areas of the brain that develop from them (see Image.  Forebrain or Prosencephalon) .  [13]

Prosencephalon (Forebrain)

• Cerebral cortex
• Basal ganglia (caudate nucleus, putamen, and globus pallidus)
• Hippocampus
• Lateral ventricles
• Hypothalamus
• Epithalamus (pineal gland)
• Subthalamus
• Posterior pituitary
• Optic nerve
• Third ventricle

Mesencephalon (midbrain)

• Cerebral aqueduct

Rhombencephalon (hindbrain)

• Fourth ventricle (rostral)
• Fourth ventricle (caudal)
• Organ Systems Involved

The brain and the spinal cord comprise the central nervous system (CNS). The peripheral nervous system (PNS) subdivides into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS consists of peripheral nerve fibers that collect sensory information to the CNS and motor fibers that send information from the CNS to skeletal muscle. The ANS functions to control the smooth muscle of the viscera and glands and consists of the sympathetic nervous system (SNS), the parasympathetic nervous system (PaNS), and the enteric nervous system (ENS).

Nerves from the brain connect with multiple parts of the head and body, leading to various voluntary and involuntary functions. The ANS drives basic functions that control unconscious activities such as breathing, digestion, sweating, and trembling.

The ENS provides the intrinsic innervation of the gastrointestinal system and is the most neurochemically diverse branch of the PNS. [14]  Neurotransmitters such as norepinephrine, epinephrine, dopamine, and serotonin have recently been a topic of interest due to their roles in gut physiology and CNS pathophysiology, as they aid in regulating gut blood flow, motility, and absorption. [15]

The cerebrum controls motor and sensory information, conscious and unconscious behaviors, feelings, intelligence, and memory. The left hemisphere controls speech and abstract thinking (the ability to think about things that are not present). In contrast, the right hemisphere controls spatial thinking (thinking that finds meaning in the shape, size, orientation, location, and phenomena). See Figure. Homunculus, Sensory and Motor.

The motor and sensory neurons descending from the brain cross to the opposite side in the brainstem. This crossing means that the right side of the brain controls the motor and sensory functions of the left side of the body, and the left side of the brain controls the motor and sensory functions of the right side of the body. Hence, a stroke affecting the left brain hemisphere, for example, will exhibit motor and sensory deficits on the right side of the body.

Sensory neurons bring sensory input from the body to the thalamus, which then relays this sensory information to the cerebrum. For example, hunger, thirst, and sleep are under the control of the hypothalamus.

The cerebrum is composed of four lobes:

• Frontal lobe: Responsible for motor function, language, and cognitive processes, such as executive function, attention, memory, affect, mood, personality, self-awareness, and social and moral reasoning. [16]  The Broca area is located in the left frontal lobe and is responsible for the production and articulation of speech.
• Parietal lobe: Responsible for interpreting vision, hearing, motor, sensory, and memory functions. 
• Temporal lobe: In the left temporal lobe, the Wernicke area is responsible for understanding spoken and written language. The temporal lobe is also an essential part of the social brain, as it processes sensory information to retain memories, language, and emotions. [17]  The temporal lobe also plays a significant role in hearing and spatial and visual perception.
• Occipital lobe: The visual cortex is located in the occipital lobe and is responsible for interpreting visual information. See Figure.  Areas of localization, Lateral Surface of Hemisphere. 

The cerebellum controls the coordination of voluntary movement and receives sensory information from the brain and spinal cord to fine-tune the precision and accuracy of motor activity. The cerebellum also aids in various cognitive functions such as attention, language, pleasure response, and fear memory. [18]

The brainstem acts as a bridge that connects the cerebrum and cerebellum to the spinal cord (see Image. Pathways From the Brain to the Spinal Cord). The brainstem houses the principal centers that perform autonomic functions such as breathing, temperature regulation, respiration, heart rate, wake-sleep cycles, coughing, sneezing, digestion, vomiting, and swallowing. The brainstem contains both white and gray matter. The white matter consists of fiber tracts (neuronal cell axons) traveling down from the cerebral cortex for voluntary motor function and up from the spinal cord and peripheral nerves, allowing somatosensory information to travel to the highest parts of the brain. [19]

The brain represents 2% of the human body weight and consumes 15% of the cardiac output and 20% of total body oxygen. The resting brain consumes 20% of the body's energy supply. When the brain performs a task, the energy consumption increases by an additional 5%, proving that most of the brain's energy consumption gets used for intrinsic functions.

The brain uses glucose as its principal source of energy. During low glucose states, the brain utilizes ketone bodies as its primary energy source. During exercise, the brain can use lactate as a source of energy.

In the developing brain, neurons follow molecular signals from regulatory cells like astrocytes to determine their location, the type of neurotransmitter they will secrete, and with which neurons they will communicate, leading to the formation of a circuit between neurons that will be in place during adulthood. In the adult brain, developed neurons fit in their corresponding place and develop axons and dendrites to connect with the neighboring neurons. [20]

Neurons communicate via neurotransmitters released into the synaptic space, a 20 to 50-nanometer area between neurons. The neuron that releases the neurotransmitter into the synaptic space is called the presynaptic neuron, and the neuron that receives the neurotransmitter is called the postsynaptic neuron. An action potential in the presynaptic neuron leads to calcium influx and the subsequent release of neurotransmitters from their storage vesicle into the synaptic space. The neurotransmitter then travels to the postsynaptic neuron and binds to receptors to influence its activity. Neurotransmitters are rapidly removed from the synaptic space by enzymes. [21]

The oligodendrocytes in the CNS produce myelin. Myelin forms insulating sheaths around axons to allow the swift travel of electrical impulses through the axons. The nodes of Ranvier are gaps in the myelin sheath of axons, allowing sodium influx into the axon to help maintain the speed of the electrical impulse traveling through the axon. This transmission is called saltatory nerve conduction, the "jumping" of electrical impulses from one node to another. It ensures that electrical signals do not lose their velocity and can propagate long distances without signal deterioration. [22]

• Related Testing

Functional magnetic resonance imaging (fMRI) can track the effects of neural activity and the energy that the brain consumes by measuring components of the metabolic chain. Other techniques, such as single-photon emission computed tomography (SPECT), study cerebral blood flow and neuroreceptors. Positron emission tomography (PET) assesses the glucose metabolism of the brain. [23]  Electroencephalography (EEG) records the brain's electrical activity and is very useful for detecting various brain disorders. Advancements in these techniques have enabled a broader vision and objective perceptions of mental disorders, leading to improved diagnosis, treatment, and prognosis.

• Pathophysiology

Injury to the brain stimulates the proliferation of astrocytes, an immunological response to neurodegenerative disorders called "reactive gliosis." [24]  Damage to neural tissue promotes molecular and morphological changes and is essential in the upregulation of the glial fibrillary acidic protein (GFAP). On the other hand, epidermal growth factor receptor (EGFR) allows the transition from non-reactive to reactive astrocytes, and its inhibition improves axonal regeneration and rapid recovery. This means that when astrocytes are reactive, they proliferate and hypertrophy, leading to glial scar formation.

The microglia represent the immune and support system of the CNS. They are neuroprotective in the young brain but can react abnormally to stimuli in the aged brain and become neurotoxic and destructive, leading to neurodegeneration. [25]  As the brain ages, microglia acquire an increasingly inflammatory and cytotoxic phenotype, generating a hazardous environment for neurons. [26]  Hence, aging is the most critical risk factor for developing neurodegenerative diseases.

The brain is surrounded by cerebrospinal fluid and is isolated from the bloodstream by the blood-brain barrier (BBB). In cases like infectious meningitis and meningoencephalitis, acute inflammation causes a breakdown of the BBB, leading to the influx of blood-borne immune cells into the CNS. In other inflammatory brain disorders such as Alzheimer disease (AD), Parkinson disease (PD), Huntington disease (HD), or X-linked adrenoleukodystrophy, the primary insult is due to degenerative or metabolic processes, and there is no breakdown of the BBB. [27]

Oligodendrocyte loss can occur due to the production of reactive oxygen species or the activation of inflammatory cytokines, causing decreased myelin production and leading to conditions such as multiple sclerosis (MS). [22]

Disturbances in the neurotransmitter systems are related to these substances' production, release, reuptake, or receptor impairments and can cause neurologic or psychiatric disorders. Glutamate is the brain's most abundant excitatory neurotransmitter, while GABA is the primary inhibitory transmitter. Glycine has a similar inhibitory action in the posterior parts of the brain. Acetylcholine aids in processes such as muscle stimulation at the neuromuscular junction (NMJ), digestion, arousal, salivation, and level of attention. Dopamine is involved in the reward and motivational component, motor control, and the regulation of prolactin release. Serotonin influences mood, feelings of happiness, and anxiety. Norepinephrine is involved in arousal, alertness, vigilance, and attention. 

Cerebral oxygen delivery and consumption rates are ten times higher than global body values. [28]  Blood glucose represents the primary energy source for the brain, and the BBB is highly permeable to it. During low glucose states, the body has developed multiple ways to keep blood glucose within the normal range. As the level drops below 80 mg/dL, pancreatic beta-cells decrease insulin secretion to avoid further glucose decrease. If glucose drops further, pancreatic alpha-cells secrete glucagon, and the adrenal medulla releases epinephrine. Glucagon and epinephrine increase blood glucose levels. Cortisol and growth hormone also act to increase glucose, but they depend on the presence of glucagon and epinephrine to work.

• Clinical Significance

Damage to the Cerebrum

• Frontal lobe -  Damage to the frontal lobe causes interruption of the higher functioning brain processes, including social behavior, planning, motivation, and speech production. Individuals with frontal lobe damage may be unable to regulate their emotions, have meaningful or appropriate social interactions, maintain their past personality traits, or make difficult decisions. [29]
• Temporal lobe - The Wernicke area is located in the superior temporal gyrus in an individual's dominant hemisphere, which is the left hemisphere for 95% of people. Damage to the left (dominant) temporal lobe can lead to Wernicke aphasia. This is typically referred to as "word salad" speech, where the patient will speak fluently, but their words and sentences will lack meaning. [30]  Damage to the right (non-dominant) temporal lobe may lead to persistent talking and deficits in nonverbal memory, processing certain aspects of sound or music (tone, rhythm, pitch), and facial recognition (prosopagnosia).
• Parietal lobe -  Damage to the frontal aspect of the parietal lobe may lead to impaired sensation and numbness on the contralateral side of the body. An individual may have difficulty recognizing texture and shape and may be unable to identify a sensation and its location on their body. Damage to the middle aspect of the parietal lobe can lead to right-left disorientation and difficulty with proprioception. Damage to the non-dominant (right) parietal lobe may lead to apraxia (difficulty with performing purposeful motions such as combing hair or brushing teeth) and difficulty with spatial orientation and navigation (they may get lost in a once familiar area). Patients with non-dominant parietal lobe damage, usually from a middle cerebral artery stroke, may neglect the side opposite of the brain damage (usually the left side), which may manifest as only shaving the right side of their face or drawing a clock with all of the numbers on the right side of the circle. [31]
• Occipital lobe -  Damage to the occipital lobe may lead to visual defects, color agnosia (inability to identify colors), movement agnosia (difficulty recognizing object movements), hallucinations, illusions, and the inability to recognize written words (word blindness). 

Damage to the Cerebellum

Damage to the cerebellum can lead to ataxia, dysmetria, dysarthria, scanning speech, dysdiadochokinesis, tremor, nystagmus, and hypotonia. To test for possible cerebellar dysfunction, a bedside neurologic exam is commonly the first step. This exam may include the Romberg test, heel-to-shin test, finger-to-nose test, and rapid alternating movement test. [32]

Damage to the Brainstem

Damage to the brainstem may present as muscle weakness, visual changes, dysphagia, vertigo, speech impairment, pupil abnormalities, insomnia, respiratory depression, or death.

Neurodegenerative Diseases

Neuronal degeneration worsens with age and can affect different areas of the brain leading to movement, memory, and cognition problems.

Parkinson disease (PD) occurs due to the degeneration of the neurons that synthesize dopamine, leading to motor function deficits. Alzheimer disease (AD) occurs due to abnormally folded protein deposition in the brain leading to neuronal degeneration. Huntington disease occurs due to a genetic mutation that increases the production of the neurotransmitter glutamate. Excessive amounts of glutamate lead to the death of neurons in the basal ganglia producing movement, cognitive, and psychiatric deficits. Vascular dementia occurs due to the death of neurons resulting from the interruption of blood supply.

Although neurodegenerative diseases are not classically caused by disturbed metabolism, research has shown that there is a reduction in glucose metabolism in Alzheimer disease. [33]

Demyelinating Diseases

Demyelinating diseases result from damage to the myelin sheath that covers the nerve cells in the white matter of the brain, spinal cord, and optic nerves. For example, multiple sclerosis and leukodystrophies are a consequence of oligodendrocyte damage.

A stroke is caused by an interruption in the blood supply to the brain, which may ultimately lead to neuronal death. This condition can result in one of several neurological problems depending on the affected region.

Brain Death

Neurologic evaluation of brain death is a complicated process that non-specialists and families might misunderstand. [34]  Brain death is the complete and irreversible loss of brain activity, including the brainstem. It requires verification through well-established clinical protocols and the support of specialized tests.

Hypoglycemia

Glucose is the primary energy source responsible for maintaining brain metabolism and function. The most significant amount of glucose is used for information processing by neurons. [35]  The brain requires a continuous supply of glucose as it has limited glucose reserves. CNS symptoms and signs of hypoglycemia include focal neurological deficits, confusion, stupor, seizure, cognitive impairment, or death.

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Human Brain, Encephalon. Illustrated brain anatomy includes the cerebrum, cerebellum, and pons; the cerebral, superior, middle, and inferior peduncles; and medulla oblongata. Henry Vandyke Carter, Public Domain, via Wikimedia Commons

Forebrain or Prosencephalon. The illustration depicts the mesial aspect of a brain sectioned in the median sagittal plane, including the foramen of Monro, middle commissure, taenia thalami, habenular commissure, genu, callosum, fornix, (more...)

Areas of localization, Lateral Surface of Hemisphere. The figure depicts the motor area in red, the area of general sensations in blue, the auditory area in green, the visual area in yellow, and the psychic portions in lighter tints. Henry (more...)

Pathways From the Brain to the Spinal Cord. The figure shows the motor tract, anterior nerve roots, anterior and lateral cerebrospinal fasciculus, decussation of pyramids, geniculate fibers, internal capsule, and motor area of cortex. Henry Vandyke Carter, (more...)

Homunculus, Sensory and Motor Contributed by S Bhimji, MD

Disclosure: Kenia Maldonado declares no relevant financial relationships with ineligible companies.

Disclosure: Khalid Alsayouri declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Maldonado KA, Alsayouri K. Physiology, Brain. [Updated 2023 Mar 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Nih research matters.

May 21, 2024

Unseen details of human brain structure revealed

At a glance.

• Researchers generated a high-resolution map of all the cells and connections in a single cubic millimeter of the human brain.
• The results reveal previously unseen details of brain structure and provide a resource for further studies.

Fully understanding how the human brain works requires knowing the relationships between the various cells that make up the brain. This entails visualizing the brain’s structure on the scale of nanometers in order to see the connections between neurons.

A team of researchers, led by Dr. Jeff Lichtman at Harvard University and Dr. Viren Jain at Google Research, used electron microscopy (EM) to image a cubic millimeter-sized piece of human brain tissue at high resolution. The tissue was removed from the cerebral cortex of a patient as part of a surgery for epilepsy.

The team began by cutting the tissue into more than 5,000 slices, or sections, each of which was then imaged by EM. This yielded about 1.4 petabytes, or 1,400 terabytes, of data. Using these data, the researchers generated a 3D reconstruction of almost every cell in the sample. Results of the NIH-funded study appeared in Science on May 10, 2024.

Analysis of individual cells in the sample revealed a total of more than 57,000 cells. Most of these were either neurons, which send electrical signals, or glia, which provide various support functions to the neurons. Glia outnumbered neurons 2-to-1. The most common glial cells were oligodendrocytes, which provide structural support and electrical insulation to neurons. The one cubic mm sample also contained about 230 mm of blood vessels.

The reconstruction revealed structural details not seen before. The researchers analyzed a type of neuron, called triangular cells, that are found in the deepest layer of the cerebral cortex. Many of these adopted one of two orientations, which were mirror images of each other. The significance of this organization remains unknown.

The team used machine learning to identify synapses—the junctions through which signals pass from one cell to another. They found almost 150 million synapses. Almost all neurons formed only one synapse with a given target cell. But a small fraction formed two or more synapses to the same target. In at least one case, more than 50 synapses connected a single pair of cells. Although rare, connections of seven or more synapses between cells were much more common than expected by chance. This suggests that these strong connections have some functional significance.

The results illustrate just how complex the brain is at the cellular level. They also show the value of connectomics—the science of generating comprehensive maps of connections between brain cells—for understanding brain function.

“The word ‘fragment’ is ironic,” Lichtman says. “A terabyte is, for most people, gigantic, yet a fragment of a human brain—just a miniscule, teeny-weeny little bit of human brain—is still thousands of terabytes.”

The team has made their dataset available to the public. They have also provided various software tools to help examine the brain map. The hope is that further study of the data, by this team and others, will yield new insight into the workings of the human brain.

“This incredible advancement—the ability to capture and process over 1,000 terabytes of data from the brain—wouldn’t have been possible without a study participant’s generous donation and the important partnerships between neuroscientists, computer scientists, and engineers,” says Dr. John Ngai, director of NIH’s BRAIN Initiative. “These collaborations are central in our aim of building a full map of the human brain so we can bring cures closer to the clinic.”

—by Brian Doctrow, Ph.D.

Related Links

• Scientists Build Largest Maps to Date of Cells in Human Brain
• Complete Wiring Map of the Insect Brain
• Mapping the Mammalian Motor Cortex
• Building An Atlas of Brain Function in Mice
• 3-D Model of Human Brain Development and Disease
• An Expanded Map of the Human Brain
• Brain Mapping of Language Impairments
• Brain Basics: Know Your Brain
• The Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative

References:  A petavoxel fragment of human cerebral cortex reconstructed at nanoscale resolution. Shapson-Coe A, Januszewski M, Berger DR, Pope A, Wu Y, Blakely T, Schalek RL, Li PH, Wang S, Maitin-Shepard J, Karlupia N, Dorkenwald S, Sjostedt E, Leavitt L, Lee D, Troidl J, Collman F, Bailey L, Fitzmaurice A, Kar R, Field B, Wu H, Wagner-Carena J, Aley D, Lau J, Lin Z, Wei D, Pfister H, Peleg A, Jain V, Lichtman JW. Science . 2024 May 10;384(6696):eadk4858. doi: 10.1126/science.adk4858. Epub 2024 May 10. PMID: 38723085.

Funding:  NIH’s Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative, National Institute of Mental Health (NIMH), National Institute of Neurological Disorders and Stroke (NINDS), and National Institute of Biomedical Imaging and Bioengineering (NIBIB); Stanley Center for Psychiatric Research at the Broad Institute; National Science Foundation; Intelligence Advanced Research Projects Activity.

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• How your brain works

The brain and nervous system

The brain contains billions of nerve cells arranged in patterns that coordinate thought, emotion, behavior, movement and sensation.

A complicated highway system of nerves connects the brain to the rest of your body, so communication can occur in seconds. Think about how fast you pull your hand back from a hot stove. While all the parts of the brain work together, each part is responsible for a specific function — controlling everything from your heart rate to your mood.

The cerebrum is the largest part of the brain. It's what you probably visualize when you think of brains in general. The outermost layer of the cerebrum is the cerebral cortex, also called the "gray matter" of the brain. Deep folds and wrinkles in the brain increase the surface area of the gray matter, so more information can be processed.

The cerebrum is divided by a deep groove, also known as a fissure. The groove divides the brain into two halves known as hemispheres. The hemispheres communicate with each other through a thick tract of nerves called the corpus callosum at the base of the groove. In fact, messages to and from one side of the body are usually handled by the opposite side of the brain.

Lobes of the brain

The brain's hemispheres have four lobes.

• The frontal lobes help control thinking, planning, organizing, problem-solving, short-term memory and movement.
• The parietal lobes help interpret feeling, known as sensory information. The lobes process taste, texture and temperature.
• The occipital lobes process images from your eyes and connect them to the images stored in your memory. This allows you to recognize images.
• The temporal lobes help process information from your senses of smell, taste and sound. They also play a role in memory storage.

Cerebellum and brainstem

The cerebellum is a wrinkled ball of tissue below and behind the rest of the brain. It works to combine sensory information from the eyes, ears and muscles to help coordinate movement. The cerebellum activates when you learn to play the piano, for example.

The brainstem links the brain to the spinal cord. It controls functions vital to life, such as heart rate, blood pressure and breathing. The brainstem also is important for sleep.

The inner brain

Structures deep within the brain control emotions and memories. Known as the limbic system, these structures come in pairs. Each part of this system is present in both halves of the brain.

• The thalamus acts as a gatekeeper for messages passed between the spinal cord and the cerebrum.
• The hypothalamus controls emotions. It also regulates your body's temperature and controls functions such as eating or sleeping.
• The hippocampus sends memories to be stored in areas of the cerebrum. It then recalls the memories later.

Peripheral nervous system

All of the nerves in your body that are outside of the brain and spinal cord make up the peripheral nervous system.

It relays information between your brain and your extremities, such as your arms, hands, legs or feet. For example, if you touch a hot stove, pain signals travel from your finger to your brain in a split second. Your brain tells the muscles in your arm and hand to quickly take your finger off the hot stove.

Nerve cells

Nerve cells, known as neurons, send and receive nerve signals. They have two main types of branches coming off their cell bodies. Dendrites receive messages from other nerve cells. Axons carry outgoing messages from the cell body to other cells — such as a nearby neuron or muscle cell.

Interconnected with each other, neurons provide efficient, lightning-fast communication.

Neurotransmitters

A nerve cell communicates with other cells through electrical impulses when the nerve cell is stimulated. Within a neuron, the impulse moves to the tip of an axon and causes the release of chemicals, called neurotransmitters, that act as messengers.

Neurotransmitters pass through the gap between two nerve cells, known as the synapse. They then attach to receptors on the receiving cell. This process repeats from neuron to neuron as the impulse travels to its destination. This web of communication that allows you to move, think, feel and communicate.

• Brain basics: Know your brain. National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-know-your-brain#. Accessed Jan. 10, 2024.
• Anatomy of the brain. American Association of Neurological Surgeons. https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Anatomy-of-the-Brain. Accessed Jan. 10, 2024.
• Brain anatomy and functions. National Cancer Institute. https://www.cancer.gov/rare-brain-spine-tumor/tumors/anatomy/brain-anatomy-functions. Accessed Jan. 10, 2024.
• Overview of peripheral nervous system disorders. Merck Manual Professional Version. https://www.merckmanuals.com/professional/neurologic-disorders/peripheral-nervous-system-and-motor-unit-disorders/overview-of-peripheral-nervous-system-disorders. Accessed Jan. 10, 2024.
• Ciurleo R, et al. Parosmia and neurological disorders: A neglected association. Frontiers in Neurology. 2020; doi:10.3389/fneur.2020.543275.

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The Human Brain: Anatomy, and Functions,

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Presentation on theme: "The Human Brain: Anatomy, and Functions,"— Presentation transcript:

The Brain is a highly organized ORGAN that contains approximately 100 billion neurons and has a MASS of 1.4 Kilograms. The Brain is Protected by a BONY.

NERVOUS SYSTEM MCGONIGLE Intro to Psychology. Nervous System  Made up of the spinal cord and the brain  Neurons : Nerve cell – the neurons transmit.

Chapter 7 The Nervous System

The Nervous System.

Overview The Nervous System. The nervous system of the human is the most highly organized system of the body. The overall function of the nervous system.

And Brain Organization

Major Brain Structures and Functions Made by Ms. Collins Unscrupulously used by Mr. McNalis.

The Meninges Dura mater - outermost layer Arachnoid mater - no blood vessels, in between layer (resembles a spider web) Pia mater -inner membrane, contains.

Nervous System Outline

Principles of Health Science There are two main divisions of the nervous system: The Central Nervous System The Peripheral Nervous System Divisions.

Chapter 7:6 The Nervous System.

Anatomy & Physiology Nervous System.

The Human Brain: Anatomy, Functions, and Injury. Main Menu Brain Anatomy Brain Functions Injury Mechanisms.

The Amazing Brain Weighs about 3 pounds Major portions: Cerebrum

 600 mya = sponges have different tissues  550 mya = flatworm with “eyespots’  500 mya = first fish  360 mya = reptiles w/lower brains  65 mya =

ANATOMY NERVOUS SYSTEM OVERVIEW. Nervous System  The nervous system of the human is the most highly organized system of the body.  The overall function.

Unit 1D: The Central Nervous System

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Science 101: The Brain

The brain constitutes only about two percent of the human body, yet it is responsible for all of the body's functions. Learn about the parts of the human brain, as well as its unique defenses, like the blood-brain barrier.

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Exercising body & brain: the effects of physical exercise on brain health

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The relationship between physical exercise and brain health is a burgeoning field of research in neuroscience, with a pivotal impact on our understanding of cognitive well-being, mental health, and aging. Existing studies evidence the positive influences of regular physical activity on brain health, suggesting its implications on learning, memory, and mood. Despite significant advancements, comprehensive analysis incorporating broader perspectives and deeper explorations remain scarce. The objective of this Research Topic is to create an enriching platform for focused discourse on the interconnection between physical exercise and brain health. The goal is to bring together theoretical and experimental research papers that depict a comprehensive overview of recent developments, examine the mechanistic underpinnings of the exercise-brain interaction, and delve into the future potential of this promising area. We welcome contributions that explore, but are not limited to, the following themes: • Impact of various types of exercises on mental health and cognitive functions. • Role of physical activity in stress, anxiety, and mood disorders management. • The molecular and neurochemical effects of exercise on the brain. • Exercise mitigating neurodegenerative disorders and age-related cognitive decline. • Effects of physical exercise on brain development and neuroplasticity. Manuscript types desired for this topic are Original Research, Review, Systematic Review, Mini Review, Perspective, and Opinion articles. Emphasis is on rigorous and high-quality methodology, analysis, and data presentation. The Research Topic places a high priority on interdisciplinary approaches and the potential practical implications of research findings.

Keywords : yoga, physical exercise, mental health

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The Human brain (Edexcel A-level biology A)

Subject: Biology

Age range: 16+

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This lesson describes the location and functions of the cerebral hemispheres, cerebellum, medulla oblongata and hypothalamus. The engaging PowerPoint and accompanying resources have been designed to cover point 8.8 of the Pearson Edexcel A-level biology A (SNAB) specification and also includes descriptions of the link between the hypothalamus and the anterior and posterior lobes of the pituitary gland.

The lesson begins with a multiple-choice question, where the students will learn that cerebrum is the Latin word for brain. This brain structure is described as two hemispheres and students will be introduced to the localisation of function of the 4 lobes of the cerebral cortex. It moves onto the cerebellum, focusing on its role of perfecting and coordinating movement, and explains how this is achieved through neural connections with the cerebrum. The control of heart rate by the medulla oblongata is described before the lesson concludes with an exploration of the connections between the hypothalamus and the two lobes of the pituitary gland, specifically in the mechanisms of osmoregulation and thermoregulation.

This is an extensive lesson covering a lot of detail, so as shown in the cover image, the lesson plan contains 5 quiz rounds as part of a competition which will help to maintain engagement whilst checking on their recall and understanding of content. There are also multiple understanding and prior knowledge checks which allow the students to assess their progress against the current topic and to make links to previously covered content. All answers to these knowledge checks are embedded into the PowerPoint.

It is likely that this lesson will take between 2 - 3 hours of teaching time, but sections can be edited and removed if the teacher doesn’t want to look at a particular structure in that detail at this stage of study.

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Topic 8: Grey matter (Edexcel A-level Biology A)

The 8 lessons included in this bundle are detailed and engaging and have been filled with a variety of tasks to challenge the students on their understanding of the content of topic 8, which is titled GREY MATTER. These lessons cover the earlier specification points in this topic, focusing on the conduction of impulses through the mammalian nervous system. If you would like to view the quality of these lessons, then download the neurones, pupil dilation and nervous and hormonal control lessons as these have been uploaded for free.

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What does spaceflight do to the human body? | Explained Premium

The average maximum time an astronaut spends in space has increased from one month in the 1960s to six months in the 2020s.

Updated - August 27, 2024 11:25 am IST

Published - August 27, 2024 11:21 am IST

NASA astronauts Sunita Williams and Barry Wilmore onboard the International Space Station on July 9, 2024. | Photo Credit: NASA

The story so far: On August 24, NASA said Boeing’s Starliner crew capsule that took astronauts Sunita Williams and Barry Wilmore to the International Space Station (ISS), as part of its first crewed test flight, wasn’t safe enough to transport them back. Instead, NASA extended Williams’s and Wilmore’s stay onboard the ISS until February 2025, when they will return in a SpaceX crew capsule to be launched in September 2024. Boeing’s Starliner will have to undock and return uncrewed.

What is space?

It’s easier to identify ‘space’ millions of kilometres away from the earth than it is near the planet because the conditions transition from ‘earth-like’ to ‘space-like’ gradually. In aeronautic and astronautic circles, space begins from the Karman line, which is 100 km above sea level. Similarly, the force of gravity can be said to be approaching zero several billion kilometres from a massive body but is nonetheless present. This is why the astronauts onboard the ISS experience microgravity, not zero gravity.

Thus, space may be a vast expanse but different parts of space can confront astronauts with wildly different ambient conditions. The Van Allen radiation belts around the earth are a good example. They lie above the Karman line, from 640 km to 58,000 km up. They consist of charged particles from outer space that have become trapped in the earth’s magnetic field. Researchers worked out the amount of radiation these belts expose astronauts to during the U.S. Apollo programme (not harmful) and thereon also determined astronauts’ exposure in outer space, where the belts won’t protect them. In this article, ‘space’ means above the Karman line and in microgravity conditions.

What are space’s effects on the human body?

While hundreds of astronauts have flown to space, they don’t make up a cohort large enough for researchers to study them and reliably elucidate all the effects of spaceflight on their bodies. They have also spent very different amounts of time there and have reported different symptoms after different trips. However, some broad trends have emerged centred on the body’s bones, digestion, eyes, heart, muscles and nerves. All these organs and systems in response to environmental conditions on the earth.

For example, in microgravity, bones become weaker, which might force the body to deposit the ‘excess’ mineral content in the kidneys, leading to renal stones. Food may move more slowly through the gut and lead to weight gain. Around 20% of all astronauts and 70% of those involved in long-duration spaceflight develop a disease called spaceflight-associated neuro-ocular syndrome (SANS): more fluids enter the head and build up at the back of the eye, affecting eyesight.

Because of the body’s weightless experience, the heart is required to do less work and could shrink. Similarly, other parts of the musculature could shed muscle mass and strength. The blood loses more red blood cells per day than it does on the ground (a 2022 study in Nature Medicine quantified the loss rate but couldn’t discern the cause), which means astronauts’ diets need to be adjusted to deliver more energy for their bodies to make more of these cells. The brain works constantly on the earth to help the body maintain its balance, sense of orientation, and positional stability using signals from various parts of the body, including the eyes and the inner ear. These signals deviate from ‘normal’ in space and force the brain to work harder to determine proper balance.

If these are the symptoms, researchers have identified some important shared causes: radiation exposure, confined and hostile environments, distance from the earth, and gravitation, among others. The second among them also speaks to psychological factors like fatigue, loss of morale, and a sense of helplessness vis-à-vis the astronauts’ family’s needs on the earth.

Can we counter these effects?

The more time astronauts spend in space, the more pronounced the symptoms. But whether missions are short or long, space agencies require their astronauts to adhere to a strict exercise regime and maintain predictable routines while in orbit in order to work the body without incurring stress. Agencies have also developed communication and work-management protocols that keep astronauts engaged, able to take ownership of their work, and relax.

Researchers are also studying whether various nutrients and drugs are metabolised differently in space. They have already identified some changes in metabolic pathways involved in synthesising DNA, amino acids, and phospholipids, and a condition in which excess iron in the body presents along with low urinary magnesium and potentially lower DNA stability. In a 2022 report , researchers suggested developing a more portable optical coherence tomography machine to check for SANS onboard spacecraft. If it is present, they recommended studying countermeasures to reduce the “headward fluid shift”, including applying “lower body negative pressure”, exposure to artificial gravity through “human centrifugation”, and taking drugs that lower the intracranial pressure.

This said, our understanding of the effects of spaceflight on humans is fraught with many uncertainties. A June 2024 paper in Nature Communications said researchers still need to understand which effects of spaceflight are or aren’t of “health-related importance”, avoid over-interpreting data “given the small sample sizes and the small number of studies”, establish “suitable ground controls”, and find alternative ways to replicate their findings.

One important set of studies called “space omics” involves understanding all the ways in which the body can be affected by the space environment. A famous example is NASA’s Twins Study , where scientists examined differences in the bodies of two identical twins — astronauts Mark Kelly and Scott Kelly — after the latter spent a year in space. It identified around 8,600 genes that were expressed differently between them. The June 2024 paper noted that “any permutation of [these genes] could uncover biochemical pathways that hold keys to the development of therapeutic supplements and lifestyle recommendations that better protect health in space”.

The “cell space atlas” of space omics. | Photo Credit: Nature Communications volume 15, Article number: 4952 (2024) (CC BY 4.0)

Japan’s KAKENHI programme is studying biological responses to various parts of the space environment. Europe’s Space Omics Topical Team is developing space omics tools and methods. In the U.S., the ‘Complement of Integrated Protocols for Human Exploration Research’ project allows astronauts to sign up for experiments in space that will study their health in standardised ways. Scientists from around the world, including India, are part of the International Standards for Space Omics Processing to develop research and ethics guidelines.

How much time are humans spending in space?

The average maximum time an astronaut spends in space has increased from one month in the 1960s to six months in the 2020s. Each expedition to the ISS can also be up to six months long.

Assuming arbitrarily that their current trip ends on February 15, 2025, Williams and Wilmore will spend 256 days in orbit. Thus far 11 individuals have spent more than 300 days in space in a single mission. The record holder is Russia’s Valeri Polyakov (437 days from January 8, 1994) and the American record-holder is Frank Rubio (370 days from September 21, 2022). The cosmonaut Oleg Kononenko is currently the only astronaut to have spent more than 1,000 days in space across missions. The second active spacefarer on this list is the U.S.’s Peggy Whitson with 675 days.

Less than a century ago going to the moon was considered a long-duration space mission. Today the space agencies of China, India, Japan, Russia, and the U.S., among others, are contemplating permanent stations on the moon and human missions to Mars. They are the new long-duration missions and they will pose newer safety challenges.

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Humphreys leads study on brain changes during pregnancy and potential effects on mental health

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Aug 28, 2024, 1:29 PM

By Jenna Somers

During pregnancy, the body undergoes dramatic physical changes. However, how brain structure and function change is not well understood. A new study aims to shed light on these changes and their potential effects on mental health throughout the peripartum period, the time during pregnancy and after giving birth. Kathryn Humphreys , associate professor of psychology and human development at Vanderbilt Peabody College of education and human development, leads the study, supported by a five-year, $3.9 million grant from the National Institute of Mental Health.

The peripartum period is marked by significant biological changes and high rates of depression. To better understand the implications of brain changes on mental health, the study seeks to characterize those changes throughout the full 40 weeks of pregnancy. To support this work, Humphreys is collaborating with a multidisciplinary team of researchers in depression, imaging science, bioethics, and maternal-fetal medicine.

The research team will study brain changes in 100 pregnant participants who will undergo a series of MRI scans. The team will use an innovative data collection design, known as planned missingness, to scan each participant only four times but one month apart from each other. This approach will allow the researchers to discover unprecedented insights into brain changes that occur across the full course of pregnancy without overburdening participants. It also will allow them to examine individual- and group-level brain changes and draw conclusions about these changes across early, middle, and late pregnancy.

The study will focus on three primary aims: to characterize alterations in brain structure and function across pregnancy, to investigate hormonal fluctuations that may be responsible for these changes, and to examine the potential consequences of changes in structure and function.

According to Humphreys, preliminary data suggests that the total brain volume, and in particular cortical thickness, decreases during pregnancy. The hormone, progesterone, may partially explain reductions in gray matter volume. To explore potential functional consequences to changes in the brain, the research team will collect electroencephalogram (EEG) data on participants’ reward and threat responses, collect tests of cognitive functioning, and assess self-reported emotions. Participants will also report on peripartum depressive symptoms at each assessment and at eight-weeks postpartum.

Given the limited knowledge on peripartum neurobiology, this study could fill critical knowledge gaps and lay the foundation for further study of peripartum depression as well as its impacts on individuals and families.

Research team members include faculty from Vanderbilt Peabody College and Vanderbilt University Medical Center:

• Ellen Clayton , professor of pediatrics and of law
• David Cole , Patricia and Rodes Hart Professor of Psychology
• Autumn Kujawa , associate professor of psychology and human development
• Sarah Osmundson , vice chair of research and associate professor of obstetrics and gynecology
• Saikat Sengupta , research associate professor of radiology and radiological science
• Seth Smith , professor of radiology and radiological sciences and associate director of the Vanderbilt University Institute of Imaging Science

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Kujawa leads study to predict postpartum depression by examining brain function throughout pregnancy

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