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The peripheral
nervous system is the nervous tissue outside the brain and spinal cord and
include somatic and autonomic nerve, end organ receptors and supporting
structures.
The major peripheral nerve trunks form by fusion and division of segmental
spinal nerves and often contains a mixture of sensory, motor and autonomic
elements.
During the formation of peripheral nerve, the Schwann cells migrate
peripherally from the spinal ganglia, orient themselves parallel to the
axons and encase them.
In myelinated nerves, one axon segment is encased by one Schwann cell.
In nonmyelinated nerves, several axon segments are encased by a common
Schwann cell.
In a fully
developed nerve a layer of connective tissue or Epineurium surrounds the
entire nerve trunk. Each peripheral nerve trunk is composed of one or
more bundles or fascicles of nerve fibres.
Each nerve fascicle is surrounded by a well defined sheath known as
Perineurium.
Within the fascicles individual nerve fiber with its investing Schwann
cell is surrounded by Endoneurium.
Image
1
; Image
2
Special stains used to identify the different components:
Perineurium-
EMA positive
Schwann cells-
S100 positive
Axons-
Neurofilament positive.
Silver stains selectively stain the axon.
Myelin-
Luxol fast blue
stain
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