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Figure 6.2
Figure
Figure
Figure 6.2 Reflex arc
Figure 6.26.2
6.2
Can you now trace the sequence of events which occur when a bright
light is focussed on your eyes?
6.1.2 Human Brain
Is reflex action the only function of the spinal cord? Obviously not, since
we know that we are thinking beings. Spinal cord is made up of nerves
which supply information to think about. Thinking involves more
complex mechanisms and neural connections. These are concentrated
in the brain, which is the main coordinating centre of the body. The
brain and spinal cord constitute the central nervous system (Fig. 6.3).
They receive information from all parts of the body and integrate it.
We also think about our actions. Writing, talking, moving a chair,
clapping at the end of a programme are examples of voluntary actions
which are based on deciding what to do next. So, the brain also has to
send messages to muscles. This is the second way in which the nervous
system communicates with the muscles. The communication between
the central nervous system and the other parts of the body is facilitated
by the peripheral nervous system consisting of cranial nerves arising
from the brain and spinal nerves arising from the spinal cord. The brain
thus allows us to think and take actions based on that thinking. As you
will expect, this is accomplished through a complex design, with different
parts of the brain responsible for integrating different inputs and outputs.
The brain has three such major parts or regions, namely the fore-brain,
mid-brain and hind-brain.
The fore-brain is the main thinking part of the brain. It has regions
which receive sensory impulses from various receptors. Separate areas
of the fore-brain are specialised for hearing, smell, sight and so on. There
are separate areas of association where this sensory information is
interpreted by putting it together with information from other receptors
as well as with information that is already stored in the brain. Based on
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