Peripheral Nervous System (PNS)

The peripheral nervous system connects the central nervous system with the rest of the body. All motor, sensory and autonomic nerve cells and fibers outside the CNS are generally considered part of the PNS. Specifically, the PNS comprises the ventral (motor) nerve roots, dorsal (sensory) nerve roots, spinal ganglia, and spinal and peripheral nerves, and their endings, as well as a major portion of the autonomic nervous system (sympathetic trunk). The first two cranial nerves (the olfactory and optic
nerves) belong to the CNS, but the remainder belong to the PNS.

Peripheral nerves may be purely motor or sensory but are usually mixed, containing variable fractions of motor, sensory, and autonomic nerve fibers (axons). A peripheral nerve is made up of multiple bundles of axons, called fascicles, each of which is covered by a connective tissue sheath (perineurium). The connective tissue lying between axons within a fascicle is called endoneurium, and that between fascicles is called epineurium. Fascicles contain myelinated and unmyelinated axons, endoneurium, and capillaries. Individual axons are surrounded by supportive cells called Schwann cells. A single Schwann cell surrounds several axons of unmyelinated type. Tight winding of the Schwann cell membrane around the axon produces the myelin sheath that covers myelinated axons. The Schwann cells of a myelinated axon are spaced a small distance from one another; the intervals between them are called nodes of Ranvier. The nerve conduction velocity increases with the thickness of the myelin sheath. The specialized contact zone between a motor nerve fiber and the muscle it supplies is called the neuromuscular junction or motor end plate. Impulses arising in the sensory receptors of the skin, fascia, muscles, joints, internal organs, and other parts
of the body travel centrally through the sensory (afferent) nerve fibers. These fibers have their cell bodies in the dorsal root ganglia (pseudounipolar cells) and reach the spinal cord by way of the dorsal roots.

1 Response to "Peripheral Nervous System (PNS)"

Chloe mengatakan...

I only know it belongs to the nervous system, nothing more about its definition and functions.
So I was wondering whether it is connected with certain diseases like autism.
Any ideas?

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