By now we know that our nerve cells send
 
the signals from the organs to the brain.
 
The brain then does all the thinking and
 
it passes the process information back
 
to the organs. So we can say that brain
 
is the main coordinating organ in our
 
body. But what about reflex actions, they
 
are coordinated by spinal cord. So we can
 
say that brain and spinal cord
 
both are very crucial for our nervous
 
system. These brain and spinal cord are
 
one of the most delicate organs of our
 
body and so they are covered by cranial
 
box and vertebral column respectively
 
for the protection. Brain and spinal cord
 
together form the central nervous system
 
or CNS while the remaining part of the
 
nervous system is called peripheral
 
nervous system or PNS. Now this PNS
 
consists of the nerve from brain that is
 
the cranial nerves and nerve from spinal
 
cord that is the spinal nerves and it
 
then connect these cranial and spinal
 
nerves to all the parts of our body. So it
 
can be said that the main function of
 
PNS is to connect the CNS to all the
 
sensory organs.
 
Now let's see the structure of the brain.
 
The outermost part of the brain is
 
called cranium or skull. It is a bony
 
box which protects the brain from
 
external injuries.
 
It has a fluid in it which also helps in
 
shock absorption of brain. Our brain has three main
 
parts; forebrain, midbrain and hindbrain.
 
So now let's discuss about all these
 
parts one by one. As the name suggests
 
fore brain is the forward most part of
 
the brain. It is the largest part which
 
consists of hypothalamus and cerebrum. It
 
is in this part that the main thinking
 
of the brain is done. Forebrain receives
 
sensory impulses from different sensory
 
receptors and then process them and send
 
them back.
 
It has separate areas for receiving
 
different sensory impulses like hearing,
 
smelling, seeing etc. It also takes care
 
of more complex sensations in nature. For
 
example it tells us about the sensations
 
of hunger.
 
It tells us when to start or stop eating.
 
Fore brain also has areas where the sensory
 
information from all the receptors is
 
put together and is interpreted. This
 
information is then transferred to the
 
motor area of the forebrain where the
 
main thinking is done. Now we'll discuss
 
about the midbrain. It is the middle part
 
of the brain. It is involved in
 
activities like sleep, wakefulness, pain,
 
perception etc. It is also involved in
 
changing the size of the pupil when we
 
stand in bright light.
 
Hind brain is the last part of the
 
brain. As you can see in the diagram it
 
consists of three parts; Pons, medulla
 
and cerebellum. It controls the wider
 
functions of our body like breathing,
 
digestion, controlling heartbeat, blood
 
pressur, etc. All these actions like
 
breathing, digestion, maintaining
 
heartbeat, maintaining blood pressure,
 
which are not in control of our will are
 
called involuntary actions; while all the
 
actions like running, speaking, walking
 
which are in control of our will
 
are called voluntary actions. So now can
 
we say that the involuntary actions are
 
also the reflex actions. Of course we can.
 
Now the question arises that how do
 
these nerve tissue cause these actions or
 
movements? We've talked about that the
 
brain sends the processed information to
 
the nerve cells which in turn sends them to
 
the muscle tissues in our body which
 
caused these movements. But the question
 
how do these muscle cells move is still
 
unanswered. The notion is that these
 
muscles move because of the change in
 
their shape and this change in their
 
shape is cause by a special protein in
 
them. When these proteins receive
 
electrical impulses from nerves cells, they
 
change their shape and arrangement in
 
the cells and this change in shape and
 
arrangement of proteins present in
 
muscle cells is responsible for muscular
 
movement. Now let's have a quick recap. We
 
just learn that central nervous system
 
consists of the brain and spinal cord.
 
while peripheral nervous system consists of
 
the nerves cells outside the brain and
 
the spinal cord. We saw that the brain is
 
made up of three main parts; forebrain
 
midbrain and hindbrain. Fore brain
 
controls all the voluntary activities of
 
our body, while midbrain and hindbrain
 
controls all the involuntary or the
 
reflex actions of one body. Next we
 
studied how nervous tissue cause muscular
 
movements. When proteins in the muscle
 
receives electrical impulses from nerves
 
they change their shape and arrangement
 
in the cells as a result the muscles
 
move.
