Monday, November 14, 2011
Peripheral Nervous System
The peripheral nervous system is composed of nerves and ganglia located outside the central nervous system (brain, spinal cord), that is to say outside the skull and spinal column. The peripheral nervous system (PNS) includes the cranial nerves, which emerge through holes (foramina) in the base of the skull, and the spinal nerves, which come out through spaces between the vertebrae (intervertebral foramina). The peripheral nerves extend to muscles and skin areas, forming nerve plexuses before entering the limbs: the brachial plexus and the lumbosacral plexus in which the fibers of the spinal nerves intermingle; as a result, the nerves of the limbs contain portions of different spinal nerves. At the entry points of the afferent nerve fibers lie ganglia; these are small oval bodies containing sensory neurons.