Structure of the Peripheral Nerve

Structure of the Peripheral Nerve

The peripheral nerve consists of both unmyelinated and myelinated fibers. In adults, the myelinated segments measure approximately 1 mm and the gaps between the myelin segments, called the nodes of Ranvier, measure approximately 1 μm. The myelin has a low capacitance (ability to store electrical charge) and a large resistance to electrical current that attempts to escape from the axon to the exracellular space.  High concentrations of Na channels are present only at the nodes of Ranvier, which enables saltatory (leaping) conduction only through the nodes of Ranvier.

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Endoneurium – made up of fibroblasts and collagen and forms the supporting structure around individual nerve fibers. The endoneurium contains endoneurial fluid which is the PNS equivalent to CSF of the CNS. PNS injuries can be identified by checking for increased amounts of endoneurial fluid using magnetic resonance neurography.

Perineuriumsupportive collagenous tissue with surrounds fascicles composed of bundles of individual nerve fibers. In peripheral nerves, funiculi will blend together and separate multiple times over short distances within the epineurium producing a meshwork of merging and diverging nerve fibers known as the funicular plexus

EpineuriumOuter supportive layer of connective tissue which contains elastic fibers and fatty tissue which bind fascicles to each other. Where spinal nerves exit the vertebral canal through intervertebral foramen, 2 layers of spinal meninges (the arachnoid and dura) invaginate the nerve to form a dural sleave of connective tissue, which is the epineurium.

Nerve Structure

Degrees of PN Injury

 

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