Somatic nervous system

The somatic nervous system describes a broad range and distribution of neurones which are involved with the innervation of skeletal muscle, connective tissue and skin. A general theme of the somatic nervous system is interaction with the environment. On the whole, its activity is under voluntary, i.e. conscious, control or modulation.

The somatic nervous system has both motor and sensory divisions:

• motor:
  • somatic efferent fibres which innervate skeletal muscle
  • may be present in:
    • spinal nerves to extracranial skeletal muscle
    • cranial nerves III, IV, VI and XII to cranial skeletal muscle
• sensory:
  • general somatic afferent fibres:
    • relay sensations such as touch, pain and temperature
    • present in spinal nerves and cranial nerves V, VII, IX and X
  • special somatic afferent fibres:
  • no equivalent fibres within the spinal nerves
    • conduct sensations of hearing and balance

The somatic nervous system must be contrasted with the autonomic nervous system.