Peripheral Neural System (PNS)

The peripheral neural system (PNS) covers every bit of nervous tissue that lies outside the CNS — this includes nerves (cord-like bundles enclosing many neurons), ganglia (small clusters of neuron cell bodies found outside the brain and spinal cord), enteric plexuses (extensive neuron networks in the walls of the gastrointestinal tract that help regulate digestion), and sensory receptors, which respond to environmental change by firing impulses inward along afferent fibres toward the CNS. The PNS itself is organised around two families of nerves.

Cranial nerves number 12 pairs in total; the first two pairs arise directly from the forebrain, while the remaining ten pairs arise from the midbrain. With the single exception of the Vagus nerve, which extends down into the abdomen, all cranial nerves serve structures of the head and face — carrying sensory information (like smell, sight, and taste/touch), motor commands (like eye movement or speech), or, in the case of 'mixed' nerves, both at once. Spinal nerves number 31 pairs, each emerging from the spinal cord through gaps between adjacent vertebrae called intervertebral foramina, and each named for the region of the vertebral column it exits from: 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and a single pair of coccygeal nerves. Every spinal nerve is a **mixed …