Exploring Brain Basics
A Brief Fact Sheet from the Neuroscience Initiative
For further information on neuroscience and brain disorders,
please visit our Knowledge Center for articles on
a wide-range of brain related topics or our
Distance Education Division
for structures free and open-access structured courses, programs, and
Why Study the 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. The brain is the crown jewel of the human body that warrants your
For centuries, scientists and philosophers have been fascinated by the brain,
but until recently they viewed the brain as nearly incomprehensible. Now,
however, the brain is beginning to relinquish its secrets. Scientists have
learned more about the brain in the last decase than in all previous centuries
because of the accelerating pace of research in neurological and behavioral
science and the development of new research techniques. As a result, Congress
named the 1990s the "Decade of the Brain".
This resource is a basic introduction to the human brain. It may help you
understand how the healthy brain works, how to keep it healthy, and what happens
when the brain is diseased or dysfunctional.
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How is the Brain
The brain is like a committee of experts. All the parts of the brain work
together, but each part has its own special properties. The brain can be divided
into three basic units: the forebrain, the midbrain, and the hindbrain.
The hindbrain (12) includes the upper part of the
spinal cord, the brain stem, and a wrinkled ball of tissue called the cerebellum
(1). The hindbrain controls the body’s vital functions
such as respiration and heart rate. The cerebellum coordinates movement and is
involved in learned rote 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 (11), which controls some reflex actions and is
part of the circuit involved in the control of eye movements and other voluntary
movements. The forebrain (10) is the largest and most
highly developed part of the human brain: it consists primarily of the cerebrum
(2) and the structures hidden beneath it.
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
intellectual activities. It holds your memories, allows you to plan, enables you
to imagine and think. It allows you to recognize friends, read books, and play
The cerebrum is split into two halves (hemispheres) by a deep fissure.
Despite the split, the two cerebral hemispheres communicate with each other
through a thick tract of nerve fibers that lies at the base of this fissure.
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
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
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How Do We Think?
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, starting with the two
frontal lobes (3), which 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. In the rearmost portion of each frontal lobe is a
motor area (4), which helps control voluntary movement. A nearby place on the
left frontal lobe called Broca’s area (5) allows thoughts to be transformed into
When you enjoy a good meal—the taste, aroma, and texture of the food—two
sections behind the frontal lobes called the parietal lobes (6) are at work. The
forward parts of these lobes, just behind the motor areas, are the primary
sensory areas (7). These areas receive information about temperature, taste,
touch, and movement from the rest of the body. Reading and arithmetic are also
functions in the repertoire of each parietal lobe.
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 (8), process
images from the eyes and link that information with images stored in memory.
Damage to the occipital lobes can cause blindness.
The last lobes on our tour of the cerebral hemispheres are the temporal lobes
(9), 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 seem to
integrate memories and sensations of taste, sound, sight, and touch.
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How Does the Brain
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 (13) contains the nucleus, where most of the molecules that the neuron
needs to survive and function are manufactured. Dendrites (14) 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 may travel
away from the cell body down an axon (15) 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 sheath
(16). This sheath can include a fatty molecule called myelin, 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. Or axons may be very long, such
as those that carry messages from the brain all the way down the spinal cord.
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 tiny sacs (17). These
sacs release chemicals known as neurotransmitters (18) into the synapse (19).
The neurotransmitters cross the synapse and attach to receptors (20) 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.
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the Common Neurotransmitters?
Acetylcholine is called an excitatory neurotransmitter because it generally
makes cells more excitable. 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.
GABA (gamma-aminobutyric acid) is called an inhibitory neurotransmitter
because it tends to make cells less excitable. It 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
Serotonin is an inhibitory neurotransmitter that constricts blood vessels and
brings on sleep. It is also involved in temperature regulation. Dopamine is an
inhibitory neurotransmitter 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
behavioral disorders work by modifying the action of dopamine in the brain.
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How Can the Brain
When the brain is healthy it functions quickly and
automatically. But when problems occur, the results can be devastating. Some 50
million people in this country—one in five—suffer from damage to the nervous
system. The NINDS supports research on more than 600 neurological diseases. Some
of the major types of disorders include: neurogenetic diseases (such as
Huntington’s disease and muscular dystrophy), developmental disorders (such as
cerebral palsy), degenerative diseases of adult life (such as Parkinson’s
disease and Alzheimer’s disease), metabolic diseases (such as Gaucher’s
disease), cerebrovascular diseases (such as stroke and vascular dementia),
trauma (such as spinal cord and head injury), convulsive disorders (such as
epilepsy), infectious diseases (such as AIDS dementia), and brain tumors.
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For further information on neuroscience and brain
disorders, please visit our Knowledge Center for
articles on a wide-range of brain related topics or our
Distance Education Division for
structures free and open-access structured courses, programs, and campaigns.
Adopted from the
of Neurological Disorders and Stroke