What is the peripheral nervous system?

The peripheral nervous system consists of all the nerves found outside the brain and the spinal cord. The diagram above illustrates the divisions of the nervous system, and we can see that the PNS is divided into many subcategories.There are 12 pairs of cranial nerves associated with the brain, and 31 pairs of spinal nerves which leave the spinal cord. The PNS can be divided into afferent and efferent divisions.

1. Afferent: This division of the PNS carries nerve impulses towards the CNS (somatic sensory neurons from the skin and muscle, visceral sensory neurons from internal organs)

2. Efferent: This division of the PNS carries nerve impulses away from the CNS (somatic nervous system, autonomic nervous system - sympathetic and parasympathetic)

What are the divisions of the efferent PNS?

1. Somatic: The somatic nervous system is concerned with detecting changes in the external environment (through sensory neurons) and then voluntarily responds to these (via motor neurons), controlling skeletal muscle contraction

2. Autonomic: The autonomic nervous system is responsible for the control of the bodies internal environment and through homeostatic mechanisms, helps to keep the internal environment constant (homeostasis); it is mainly involuntary, and the autonomic nervous system can be further divided (see next module)