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Nervous
system 3
Monacia
Williams, Contributor
Hello
again students and welcome to another
lesson. This week we will be looking
at the brain and its functions. Again,
diagrams are here for you to learn.
For the brain, you will most likely
be asked to label rather than draw
the diagrams, so get familiar with
the labels and the functions of the
different parts.
The
brain
The
brain is a very complex structure
made up of millions of neurones. It
is surrounded by three membranes called
the meninges, which protect the brain.
Have you met the word meningitis?
You haven't? Can you guess its meaning?
If you deduced that it was an illness
caused by an infection of the meninges
or the lining of the brain, you are
correct.
The
brain coordinates your actions, the
neurones in the brain link up to enable
you to coordinate the incoming and
outgoing impulses that will determine
your actions. The brain is found in
the cranium of the skull. The cranium
has a hole through which the spinal
cord passes.
The
parts of the brain
- The
largest part of the brain is the
cerebrum which comprises two cerebral
hemispheres. The cerebrum is responsible
for conscious behavior, memory and
learning. It has special centres
for interpretation. Its surface
is deeply folded grey matter with
millions of cell bodies of neurones.
Inside the grey matter is the white
matter which is made up of the fibres
of the neurones. (In the spinal
cord the white matter is on the
outside and the grey matter is on
the inside?. The front part of the
brain is responsible for our feelings
and emotions.
- At
the base of the cerebrum is the
hypothalamus. The hypothalamus controls
osmoregulation and temperature regulation.
It produces the hormone ADH which
is then stored in the pituitary.
- The
pituitary gland is attached to the
hypothalamus and is found in the
centre of the head. It secretes
a large number of hormones, many
of which control the activities
of the other endocrine glands.
- The
cerebellum controls our sense of
balance and posture. It allows us
to make precise movements such as
walking, running or riding a bicycle.
- The
medulla oblongata is the enlarged
upper portion of the spinal cord.
It contains the centres that control
automatic actions like heartbeat,
breathing and blood pressure. It
controls the cranial reflexes of
sneezing, coughing and the production
of saliva.
Actions
which are mediated through the brain
are called voluntary actions. These
involve thoughts which may be based
on learning and memory and are determined
by the neurones of the cerebrum. This
means that the actions are not always
the same. There are times when the
brain can change what could have been
an involuntary action. For example,
if a hot object is picked up unknowingly,
the release of the object might be
influenced by the value of the object
to the person picking it up. If it
is valuable then conscious thought
will determine how it is put down.
The brain can also influence the stimulus
initiating a reflex action. These
reflexes are called conditioned reflexes
and they occur when a normal reflex
action is brought about by a stimulus
that is learnt.
The
sense organs
The
brain receives and processes information
from the sense organs. The processed
information is then sent as impulses
which determine the actions of effector
organs. The sense organs are:
- The
skin which responds to touch, pressure,
heat and cold, enabling us to respond
to our environment.
- The
tongue which responds to chemicals
in our food and drink, giving us
a sense of taste.
- The
nose which responds to chemicals
in the air, giving us a sense of
smell.
- The
ears which respond to sound vibrations
and movement, giving us a sense
of hearing and balance.
- The
eyes which respond to light rays,
giving us a sense of sight.
See
you next week when we will look at
the eye. Have a good week!
Monacia
Williams teaches at Glenmuir High
School. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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