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The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS produces and interprets signals and stimulates the PNS. In contrast, the PNS stimulates muscles and transmits inputs (sensory, excitatory, etc.) to and from the CNS.
The two main cell types of the nervous system are neurons and neuroglia. Neurons consist of the soma, or cell body, and the axon. The soma transmits the stimuli, which is usually an electrical signal, while the axon carries the stimuli to another soma or muscle. The neuroglia, or glial cells, aid and support the neurons. Neurons do not undergo mitosis; however, are capable of regenerating their axons.
Nerve guidance channels provide a solution to nerve damage in the PNS. The neurons in the PNS are surrounded by sheaths of Schwann cells, which are glial cells. The endoneurium, comprised of collagen fibers, surrounds the supporting Schwann cells and axons. Then the perineurium forms fascicles from the surrounding endoneuriums. Finally, the epineurium binds the individual fascicles to form a nerve trunk. The anatomy is depicted in Figure 1.1
Figure 1. Cross-sectional view of a PNS nerve trunk.1