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Peripheral Nerve Fibers



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Quick Facts

The endoneurium is the connective tissue in a peripheral nerve fascicle; it forms an interstitial layer around the neurilemma that surrounds individual myelinated nerve fibers and Remak bundles of unmyelinated fibers (Dorland, 2011).

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Related parts of the anatomy


The endoneurium is the connective tissue layer surrounding a nerve fiber (neuron) including the neurolemma and the myelin sheath. This connective tissue is made up of a fibrous matrix largely composed of collagen type III fibers (reticulin), which are arranged into intricate bundles, parallel to the long axis of the nerve. They tend to become somewhat concentrated around individual Schwann cell-axon units and vessels of the endoneurium. The primary cellular constituents of the endoneurium are fibroblasts, however resident macrophages and mast cells are also present (Standring, 2016).

Anatomical Relations

The endoneurium is surrounded by endoneurial fluid at a slightly higher pressure than that found external to the endoneurial channel. Within the endoneurial channel, tiny capillaries are present which are comprised of a single layer of non-fenestrated endothelial cells. These serve as part of the blood-nerve barrier (Peltonen, Alanne and Peltonen, 2013).


The endoneurium plays a role in isolating nerve signals. Each peripheral nerve contains numerous axons that transmit to several muscles in the body. The endoneurium is in control of keeping these signals separate ensuring they are transmitted to the correct location. The endoneurium also protects the delicate axons from potential harm. Another function of the endoneurium, which is shared by the perineurium and epineurium, is the protection of neurons from damage (Carp, 2015).

List of Clinical Correlates

—Advanced axonal neuropathy


Carp, S. (2015) Peripheral Nerve Injury An Anatomical and Physiological Approach for Physical Therapy Intervention. EBL-Schweitzer: F. A. Davis Company.

Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Peltonen, S., Alanne, M. and Peltonen, J. (2013) 'Barriers of the peripheral nerve', Tissue Barriers, 1(3), pp. e24956.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series: Elsevier Limited.

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