The brain is literally the nerve centre of our bodies.
More sophisticated than any computer, it sits neatly within our skulls
controlling and directing everything we do or think whether we are awake
No part of the body is more important or complicated than the brain.
It lies at the centre of a complex network of nerves that runs through
the spinal cord. It's our brains -- bigger and more sophisticated than
those of any other animal -- that make us what we are. They control
literally everything we think and do, from walking and talking to
feelings like love, jealousy, sadness and every other emotion.
The brain and the spinal cord
make up what is known as the central nervous system. This controls basic
bodily functions such as breathing, temperature and heart-rate, as well
as conscious actions such as eating, talking and moving.
The CNS is constantly receiving messages in the form of nerve
impulses from our senses, which inform the brain at all times of where
we are and what is going on around us. The brain interprets this
information and , when we decide to act on it, sends instructions down
other nerve cells called motor nerves. Sometimes, however, in situations
of danger or where survival is at stake, there simply isn't time for a
message to be interpreted by the brain. In this case, the message goes
only to the spinal cord which responds with a reflex action. Examples of
these are blinking, reactions to pain and sexual responses. When the
doctor tests the knee jerk reflex, he is checking on the speed of your
reflexes, which can indicate potential damage to the spinal cord.
All the messages flashing to and from our brains are transmitted by
minute electrical impulses, which travel through special nerve cells
known as neurons. This electrical activity can be measured by an
electroencephalogram, or EEG.
Strangely, the left side of the brain controls the right hand side of
the body and the right side of the brain controls the left hand side.
The brain cells form a mass of jelly-like tissue encased in three
layers of protective membranes called meninges and bathed in a fluid
called, cerbrospinal fluid. Four arteries in. the neck supply the brain
with the blood without which it cannot survive. In fact, the brain
receives about one fifth of the heart's output of blood.
MAPPING THE BRAIN
The brain is divided into three different regions: the hindbrain,
midbrain and forebrain. Each of these is divided into separate sections,
which are responsible for different functions and linked to other parts
of the brain.
The largest structure in the hindbrain is the cerebellum, which is in
charge of balance and co-ordination. The brain stem, which lies at the
base of the cerebellum, is the oldest, most primitive part of the
hindbrain. It is here that all incoming and outgoing messages come
together and cross over to the opposite side of the brain. The brain
stem is concerned with the vital functions of life itself. Activities
such as our heart rate, breathing, blood pressure, consciousness,
swallowing, coughing, vomiting and hiccuping are all controlled by this
part of the brain.
The reticular activating system, which is part of the brain stem, is the
area of the brain that controls consciousness. It sifts through the mass
of incoming information and decides which is important enough to alert
other regions of the brain.
It does so by controlling the amount of electrical activity each part of
the brain receives.
Just beyond the brain stem, in the midbrain, is an area which
controls eye movements. Beyond this, the forebrain begins. The
egg-shaped thalamus is located here; this acts like a relay station for
incoming sensory information.
Beneath this is the hypothalamus. This tiny region, which has close
links with the pituitary gland, is involved with bodily functions such
as hunger and thirst, regulation of body temperature, aggression, sexual
behaviour and sleep.
CENTRE OF THE EMOTIONS
Encircling the thalamus is a part of the brain called the limbic system,
which is made up a number of structures, including the septum pelucidum,
hippocampus and amygdala. Another very ancient part of the brain, the
limbic system is concerned with the emotions, and parts of the memory.
This system has close links with the sense of smell, which is one
reason why a particular smell or odour can evoke a forgotten memory more
intensely than anything else. The limbic system also relays messages
from the body's internal organs to other parts of the brain, which
explains why such sensations are tinged with emotion and goes some way
to account for phenomena such as 'nervous stomach aches'.
The largest part of the whole brain is a structure known as the
cerebrum, which is located in the forebrain. The cerebrum is more
developed in humans than in any other animal and is vital to thought,
memory, consciousness and higher mental activities. The cerebrum is
divided into two halves, or hemispheres, which are joined by a thick
bundle of nerve fibres called the corpus callosum.
The two hemispheres, although identical in appearance, have completely
different functions. For example, higher mental processes such as speech
and writing are controlled from the dominant cerebral hemisphere.
Whether you are right or left handed, the left hemisphere is usually
dominant in writing, The non-dominant right brain controls
visual/spatial orientation and tasks such as map-reading, navigation and
so on. It's also thought to be the more intuitive side of the brain,
which is used in artistic and creative thoughts and tasks.
The outer surface of the cerebrum, known as the cerebral cortex,
consists of 3mm (0.1 in) thick, wrinkled layer of grey matter, with
nerve cells arranged in six different layers.
This part of the brain is so developed that, in order to fit inside
the skull, it has to fold over into an area 30 times smaller than its
actual size, This is the region of the brain that is concerned with
conscious thought, sensation, movements, speech, and complex activities
such as writing. Sensory information reaching this part of the brain
undergoes detailed analysis before any action is initiated. So, memory,
thought and decision making all come into play.
THE FOUR LOBES
Each of the two hemispheres of the cortex are divided into four distinct
lobes -- occipital, parietal, temporal and frontal - named after the
bones of the skull that lie over them. Each of these is concerned with
different senses: the occipital lobes are concerned with vision, the
parietal with touch, the temporal with hearing and smell, and the
frontal lobes with movement and complicated thought.
Specific parts of each lobe are devoted to receiving sensory messages
from different areas of the body, so for example, there is a tiny area
in the parietal lobe devoted to sensation from the knee, while, a larger
area is devoted to sensation from the thumb. This is the reason why the
thumb is more sensitive than the knee. The frontal lobes, concerned as
they are with thought and action, are also central to our personality.
Beneath the cortex, there are tracts of nerve fibres, made up of
white matter, which connect the various areas of the cortex to each
other and also to nerve centres in the centre of the forebrain and brain
stem. Deeper still within the hemispheres are groups of cells called
basal ganglia, which are connected to the brain stem and cerebellum.
Above all, our brains are concerned with memory and learning. Memory is
a complicated process and experts are still trying to work out what
processes are involved. Whenever we think or do anything, an electrical
message passes through a brain cell and in the process changes the cell
When the same process is repeated, the cell then changes permanently
and new electrical pathways are set up which enable us to remember
something or, in other words, to learn it. In this way, a memory
literally becomes a physical part of you.
Memory doesn't take place just in one area in the brain; instead
different parts of the brain seem to store different memories, That
said, the temporal lobe and, the limbic system seem to be particularly
concerned with memory and disturbances of these can cause memory
disorders. For example, stimulating a particular part of the temporal
lobe in patients suffering from temporal lobe epilepsy often evokes the
same memory. And, similarly, patients with the illness have
uncontrollable flashbacks of past events.
Brain damage is said to occur when nerve cells or tracts have
degenerated or died. Damage may be confined to one part of the brain,
causing particular problems such as difficulty speaking, or paralysis of
one part of the body. Or it may be more widespread, causing mental or
LACK OF OXYGEN
The most common cause of brain damage is lack of oxygen to the brain,
medically known as hypoxia. Babies in the womb may be deprived of their
oxygen because of narrowing of the blood vessels. in the placenta due to
pre-eclamptic toxaemia, which is why such babies are often delivered as
early as it is safe to do so.
Other babies sustain brain damage during birth. This type of brain
damage can cause cerebral palsy, or spasticity, which results in
paralysis, abnormal movements, and sometimes mental retardation and
In adults, hypoxia may also arise due to cardiac arrest, when the
heart stops beating, respiratory arrest, or through the accumulation of
toxins in the brain due to the untreated enzyme deficiency,
Infections such as encephalitis, or inflammation of the brain, can
also cause brain damage, which is one reason why measles in some cases
can be such a serious illness.
Brain damage can be due to head injury, stroke, a brain tumour or brain
abscess, which leaves the victim with a range of handicaps. These may
include problems speaking or moving, mental handicap or even epilepsy.
Local damage to the basal ganglia can also occur at birth as a result of
haemolytic disease of the newborn.
People who have sustained brain damage, however, do eventually regain
some function as other parts of the brain take over from those that were
damaged. Younger people, especially children, tend to recover much
better than older sufferers. And children, in particular, can make
astonishing recoveries from brain damage because their brains are not so
rigidly organized as those of adults.