Peripheral Nervous System

The peripheral nervous system consists of all nerves arising from the brain and the spinal cord. Overall, it consists of two kinds of pathways:

1. Afferent (receiving) sensory pathways
2. Efferent (carrying away) motor pathways

The afferent (receiving/sensory) pathways are included in two kinds of nerves.

• Purely sensory nerves, for example the cranial nerves received from the eyes, ears, nose, etc.
• Mixed cranial nerves like the fifth (facial nerve) which contains sensory fibres bringing sensations from the face but it also contains motor fibres which carry impulses away to the jaw muscles.

The efferent (sending) pathway may be subdivided into somatic and autonomic nervous systems.

• The somatic nervous system controls the voluntary muscles. It includes most cranial nerves as well as the motor nerve fibres of the spinal nerves. Both these convey message from the CNS to the voluntary muscles.
• Autonomic nervous system innervates the involuntary muscles and the glands. It consists of a pair of chains of ganglia and nerves on either sides of the backbone. This system is essentially a motor system, which regulates the involuntary actions of the internal organs. It consists of two parts: (a) Sympathetic nervous system and (b) parasympathetic nervous system.

Sympathetic nervous system prepares the body for facing emergency situations and the parasympathetic nervous system reestablishes the normal conditions once the emergency is over.