The Epic Interactive Encyclopedia 1998/Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso/B/Brain,_Human/INFOTEXT

Text File | 1992-09-04 | 4KB | 92 lines

The human brain has two main functions.
The higher functions include memory, speech,
personality, movement and co-ordination,
judgment, reasoning, emotion, perception, and
so on. The lower functions (sometimes called
the autonomic functions) are unconscious, and
regulate the internal environment of the
body, such as core body temperature, heart
rate, intestinal activity, urine excretion,
and so on. The brain and the spinal cord
together make up the central nervous system.
The adult brain weighs about 1400 grammes,
and is composed of two basic types of cell.
Neurones are specialised brain cells, of
which there are 14,000 million in the adult.
Each neurone is joined to hundreds of others
by connections called synapses. These
synaptic networks are incredibly complicated,
and allow us to think, to feel emotion, and
to compose symphonies and fly aeroplanes. The
brain does not function in any way like a
computer. Neurones are so specialised they
have lost the ability to divide, and so if
the brain is injured, it cannot heal. Between
and around the neurones are cells called
glial cells, which surround, support and
nourish the neurones. The wrinkled surface of
the brain is called the cortex, also called
the grey matter. It is here that most
conscious thoughts and feelings take place.
The cortex is 2-3mm thick, and is wrapped
around the white matter, which is mainly
composed of connecting nerve fibres between
various parts of the cortex. Buried deep
within the white matter are islands of grey
matter called the basal ganglia, whose
function is to regulate movement and posture.
The brain is divided into two hemispheres.
The left half of the brain controls the right
side of the body, and vice versa. The
function of the hemispheres is not identical,
although they have much in common. One of the
hemispheres tends to be active more than the
other, and is called the dominant hemisphere.
In right-handed people, the dominant
hemisphere is the left. In left-handed
people, it is the other way around, although
some left-handed people have a dominant left
hemisphere. The left hemisphere is more
capable of rigid thought, logic, mathematical
reasoning, and so on. The centre of speech
production is almost always on the left, even
in left-handed people. The right is more
capable of artistic and musical expression
and creativity. Some scientists have found
that left-handed people tend to be more
artistic and creative than right-handed
people, which may reflect their dominant
right hemispheres. Different functions of the
brain are localised to different parts of it.
Speech production, for example, happens in a
small region of the cortex called Broca's
area. If Broca's area is damaged, e.g. by
injury, the person will lose the ability to
speak (a condition called aphasia), but the
other parts of the brain will function
normally. In addition, some of the areas
surrounding the damaged area will take over
some of the functioning of the damaged area,
and some functional recovery may take place,
even although healing is not possible. The
energy requirements of the brain are immense.
It receives one quarter of all blood coming
from the heart, and uses one fifth of the
body's energy. The brain floats in a clear
watery fluid called cerebrospinal fluid,
which cushions the delicate brain from
shocks and impacts, and also contains
nutrients such as glucose. The brain is well
protected inside the strong bony skull. The
spinal cord is more than simply a cable
connecting the brain to the body. It also
contains white matter and grey matter, but
the grey matter of the spinal cord is not
used in thinking, but in mediating
unconscious reflexes such as the knee-jerk
reflex. In addition, the grey matter of the
spinal cord provides important modification
of incoming pain sensations.

Subject by: Dr Aidan M. O'Donnell