Understanding the nervous system
Let's take a look at all the
different parts of the nervous system - the brain, spinal cord and
We'll briefly explain what each part does, how the different parts
of the nervous system communicate with each other and the rest of
the body, and discuss the effects of disease or damage to
The brain is the body's control center. It may
only weigh about 1.5kg but it is estimated to have about 100
billion cells. It controls everything we do, from basic body
functions (such as breathing, heart beat and blood pressure) to our
movements, speech, senses and aspects of our personality.
The brain is divided into two cerebral
hemispheres - the left hemisphere and the right hemisphere. Each
hemisphere tends to specialize in certain functions but the two
hemispheres work seamlessly together, sharing information:
- The right hemisphere tends to be more
visual, thinking in pictures. It sees, recognizes and organizes
information for the left side to analyze and process further.
Generally speaking, the right hemisphere controls muscles on the
left side of the body.
- The left hemisphere is mostly responsible
for speech, language, calculations, maths and logical abilities. It
generally controls muscles on the right side of the body.
The brain is divided further into "lobes" that
handle specific areas of function, the frontal, parietal, temporal
and occipital lobes:
- The frontal lobes look after planning,
organizing, reasoning, decision-making, judgment and the
- The temporal lobes also have a role in
language, particularly in the ability to hear and understand it.
They are concerned with memory, the emotions, the ability to enjoy
music and to recognize and identify things we see, such as faces or
- The parietal lobes are concerned with the
perception of sensations, such as touch, pressure, temperature,
pain and the understanding of words and sentences, reading and
writing and sometimes the ability to use numbers. They deal with
spatial awareness, such as our ability to find our way around a
house, to drive a car and to reach for objects.
- The occipital lobes are primarily concerned
with vision but also with our ability to recognize what we see in
terms of identifying colours, locating objects in the environment
and seeing objects accurately.
Below the cerebral hemispheres are the
cerebellum and the brain stem, which connect with the spinal
The cerebellum is involved in
"doing" rather than "thinking" activities. It carries out orders
from the cerebral hemispheres above and keeps a number of vital but
routine functions kicking over, such as maintaining balance and
ensuring our muscles move in a smooth, coordinated way.
The brain stem controls many
vital functions including breathing, blood pressure, blood
circulation, swallowing, appetite, body temperature and digestion,
as well as the need for water, staying awake and sleeping. It is
also the main route for nerve fibers running between the cerebral
hemispheres and the spinal cord. Any damage in the brain stem can
produce widespread and profound effects.
The Nervous system
The brain communicates messages through a
complex network of nerves that travel throughout our body.
Together, the brain and nerves are known as the nervous system,
while the spinal cord and the brain make up the central nervous
On their own, the nerves that run throughout
our body are called the peripheral nervous system. They relay
information from our brain through our spinal cord to the body, and
back again. The autonomic nervous system is part of the peripheral
nervous system. It conveys messages from all of the organs in our
chest, abdomen and pelvis. For example, it manages our "fight and
flight" responses, our "rest and digest" responses. It looks after
the automatic activities of our heart and blood vessels and plays
an important part in sexual response and bladder control.
Neurones - basic building
The basic building blocks of the nervous system
are nerve cells or neurones. We are born with about 100 billion
neurones that must last a lifetime. Unlike all the other cells in
the body, neurones do not replace themselves if they die or are
Gray matter is formed when
neurones cluster together on the outer part of the brain and inner
part of the spinal cord.
White matter is found on
the inner part of the brain and outer part of the spinal cord. It
is made up of bundles of nerve fibers called axons, which are
really just the long thin extensions of neurones. These axons are
covered by a white, fatty substance called myelin (hence the term
"white matter"), which insulates them, like the plastic coating of
an electric wire. The axons then bundle together, like the
individual telegraph wires in a cable, to form a nerve.
How it all works
The brain is in constant contact with all parts
of the body, sending instructions and receiving feedback from the
senses. The axons carry these messages as tiny electrical currents
or nerve impulses:
- Outgoing messages are sent from the brain
to activate the muscles of the body travel along the motor
pathways. The neurones that make up these pathways are called motor
- Incoming messages are sent from the
senses back to the spinal cord and brain come along the sensory
pathways. These are called sensory neurones.
How change affects the nervous
Various conditions from illness (encephalitis)
and incidents (heart attack, stroke) to accidents (near drowning, a
skateboarding fall) can cause brain damage, which affect the way
the nervous system functions by:
- affecting brain function itself
- affecting the brain's ability to communicate with the rest of
- affecting the ability of muscles to respond to the brain's
orders (nerve impulses).
Acquired Brain Injury
Damage to the brain is called Acquired Brain
Injury. An accident, illness or incident can cause direct injury to
the brain cells, and any interruption to the blood supply to the
brain may also cause damage. Without a constant blood supply, the
brain is unable to maintain its extraordinary level of
For example, a lack of oxygen (hypoxia) during
near drowning affects blood supply to the brain, as does severe
bleeding in other parts of the body, or any excessive pressure
within the skull, which might occur due to brain swelling or
Changes to the brain and nervous system can
lead to the following kinds of issues:
- Medical problems - headache and epilepsy are
two of the most common.
- Sensory difficulties such as sight, hearing,
touch, smell, taste, body-temperature control and awareness of body
position e.g. some people may become hypersensitive to sound, heat
or cold, while others may lose awareness of body position which
creates problems with buttoning shirts, using a spoon or stepping
off a curb safely.
- Physical difficulties such as paralysis
and limb weakness or problems with coordination, balance and
tremor. Fatigue is also very common.
- Thinking abilities including poor
concentration, memory loss and difficulties in planning,
organizing, problem-solving, abstract thinking and responding
effectively may arise. Slowness in thinking is very common.
- Communication and speech
difficulties such as slurred words or difficulty
understanding others. Some people may have trouble swallowing.
Others have difficulties using language, such as finding the right
words or understanding sentences.
- Behaviour - a person may become
aggressive, lack initiative or be poorly motivated. They may have
difficulty regulating their own behaviour in a way that is socially
acceptable e.g. a person with a brain injury may make inappropriate
- Personality changes can occur as a result
of damage to the brain. One example is having difficulty regulating
emotional responses, such as becoming irritable or laughing or
crying too easily. Personality change can also be the result of a
person's reaction to having ABI, which is often the case with
Some of the effects of a brain injury are
obvious and profound, while others are subtle, yet disabling. The
effects will vary widely from person to person and the recovery
process may continue over many years.
References and further information
This article has been
reproduced with the permission of BrainLink, from their excellent
brain injury resource available for free download at www.brainlink.org.au
This publication is split into sections covering medical issues,
common changes after a brain injury, practical assistance and
emotional issues. The website also has a wide range of fact sheets
on many other issues. BrainLink is a Victorian service dedicated to
improving the quality of life of people affected by conditions of
the brain, and providing support to their families.