The perineurium is a protective sheath that surrounds a
nerve fascicle
A nerve fascicle is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system. A nerve fascicle is also called a fasciculus, as is a nerve tract in the central nervous system.
A nerve fascicle is enclosed by perineurium, a l ...
.
This bundles together
axons
An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action pot ...
targeting the same anatomical location.
The perineurium is composed from
fibroblasts
A fibroblast is a type of biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibrobla ...
.
In the
peripheral nervous system
The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...
, the
myelin sheath
Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...
of each axon in a nerve is wrapped in a delicate protective sheath known as the
endoneurium. Fascicles, bundles of
neurons
A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...
, are surrounded by the perineurium. Several fascicles may be in turn bundled together with a
blood supply and
fatty tissue within yet another sheath, the
epineurium. This grouping structure is analogous to the muscular organization system of
epimysium,
perimysium and
endomysium.
Structure
The perineurium is composed of
connective tissue
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...
, which has a distinctly
lamellar arrangement consisting of one to several
concentric
In geometry, two or more objects are said to be ''concentric'' when they share the same center. Any pair of (possibly unalike) objects with well-defined centers can be concentric, including circles, spheres, regular polygons, regular polyh ...
layers. The perineurium is composed of perineurial cells, which are
epithelioid myofibroblasts. Perineurial cells are sometimes referred to as
myoepithelioid due to their
epithelioid and
myofibroblastoid properties including
tight junctions,
gap junctions
Gap junctions are Membrane channel, membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites.
Gap junctions were first described as ''close appositions' ...
,
external laminae and contractility. The tight junctions provide selective barrier to chemical substances.
The perineurium is a smooth, transparent tubular membrane which may be easily separated from the fibers it encloses. In contrast, the epineurium is a tough and mechanically resistant tissue which is not easily penetrated by a needle.
Clinical importance
The perineurium, as the epineurium, has a clinical importance following a trauma, like a fracture. A sort of lesion called
axonotmesis
Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory function ...
can happen, where the axon of the nerve is damaged while the integrity of the perineurium and epineurium is preserved. In that case, there will be a loss of neural transmission which will be causing a diminished response in the distal part of the nerve. The axon will be able to regenerate itself at a rate of 3 cm per month, generally indicating a return to a physiological state in roughly three months.
See also
*
Connective tissue in the peripheral nervous system
*
Endoneurium
*
Epineurium
*
Nerve fascicle
A nerve fascicle is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system. A nerve fascicle is also called a fasciculus, as is a nerve tract in the central nervous system.
A nerve fascicle is enclosed by perineurium, a l ...
References
External links
* - "Peripheral nerve"
* - "PNS, nerve (LM, Low)"
*
Diagram at HowardHistology at ucla.edu
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Neurohistology