This part of the system is made up of all of the nerves and the wiring.
This system sends the messages from the brain to the rest of the body.
The 31 pairs of spinal nerves are part of the peripheral nervous system.
There are two types of cells in the peripheral nervous system which
carries information to the sensory neuron cells and from the motor
neuron cell. Cells of the sensory nervous system send information to the
CNS from internal organs or from external stimuli.

Much of the peripheral nervous system is concerned with voluntary
response, but there are still involuntary responses that are dealt with.
This part of the PNS is called the autonomic nervous system as it deals
with automatic responses such as smooth and cardiac muscle. The
autonomic nervous system comprises of the sympathetic and
parasympathetic system. The differences between both of these are the
responses that are generated as they work in opposition to each other.
For example, the medulla of the adrenal glands is supplied with
sympathetic fibres which trigger the release of adrenaline into the
blood. The parasympathetic nervous system releases acetylcholine that
decreases the heart.