For IGCSE O-Level Biology students Chapter 12

1. Nervous system
Everything is under control!

2. Nervous system
The human nervous
system is made up of
two parts:
1. Central nervous
system CNS. Consists
of the brain and the
spinal cord.
2. Peripheral nervous
system PNS. Made up
of nerves extending
from CNS all over the
body.

3. There are two types of actions
Voluntary action Involuntary action
Requires thinking Takes place without
thinking
slower Faster
Controlled mainly by the
brain
Controlled mainly by the
spinal cord
For everyday actions Usually life saving actions

4. Reflex arc

5. A closer look at the reflex arc

6. Sensory neurone
 Sensory neurones receive the
stimulus, this starts an electrical
impulse at the nerve endings
and travels down the axon to
reach the other end of the cell.
 The myelin sheath insulates the
cell and helps to speed up the
electrical impulse.
 the electrical impulse reaches
the relay neurone that is in the
spinal cord.

7. Motor neurone
The motor neurone has
a cell body right at the
beginning of the cell
with dendrites radiating
out of it, electrical
impulse received from
the relay neurone will
travel down the axon to
reach the motor end
plate that is imbedded in
a muscle. This will
cause the muscle to
contract.