Perineurium
Encyclopedia
In the peripheral nervous system
, nerve fibers are each wrapped in a protective sheath known as the endoneurium
. These are bundled together into groups known as fascicles
, each surrounded by a protective sheath known as 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
.
The perineurium is composed of connective tissue
, which has a distinctly lamellar arrangement consisting of roughly 7-8 concentric layers. The perineurium is cellular, and 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, external laminae and contractility.
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.
Peripheral nervous system
The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
, nerve fibers are each wrapped in a protective sheath known as the endoneurium
Endoneurium
The endoneurium, also referred to as an endoneurial channel, sheath or tube, is a layer of delicate connective tissue made up of endoneurial cells that encloses the myelin sheath of a spinal cord nerve fiber. These are bundled up into groups called nerve fascicles, which have a protective sheath...
. These are bundled together into groups known as fascicles
Nerve fascicle
A small bundle of nerve fibers, enclosed by the perineurium, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or nerve fascicles, which are bound together in a common membranous...
, each surrounded by a protective sheath known as the perineurium. Several fascicles may be in turn bundled together with a blood supply and fatty tissue within yet another sheath, the epineurium
Epineurium
The epineurium is the outermost layer of connective tissue surrounding a peripheral nerve. It is made of dense irregular connective tissue and usually contains multiple nerve fascicles as well as blood vessels which supply the nerve...
. This grouping structure is analogous to the muscular organization system of epimysium
Epimysium
Epimysium is a layer of connective tissue, which ensheaths the entire muscle. It is composed of dense irregular connective tissue. It is continuous with fascia and other connective tissue wrappings of muscle including the endomysium, and perimysium. It is also continuous with tendons where it...
, perimysium
Perimysium
Perimysium is a sheath of connective tissue that groups muscle fibers into bundles or fascicles.Recent advances in muscle physiology suggest that the perimysium plays a role in transmitting lateral contractile movements...
and endomysium
Endomysium
The endomysium, meaning within the muscle, is a layer of connective tissue that ensheaths a muscle fiber and is composed mostly from reticular fibers. It also contains capillaries, nerves, and lymphatics...
.
The perineurium is composed of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
, which has a distinctly lamellar arrangement consisting of roughly 7-8 concentric layers. The perineurium is cellular, and is composed of perineurial cells, which are epithelioid
Epithelioid
An epithelioid cell is a cell that resembles epithelial cells in that it directly contacts its neighboring cells via cell surface molecules or junctions. Unlike epithelial cells, however, epithelioid cells make contacts over their entire surface, rather than at restricted portions. The term...
myofibroblasts. Perineurial cells are sometimes referred to as myoepithelioid due to their epithelioid
Epithelioid
An epithelioid cell is a cell that resembles epithelial cells in that it directly contacts its neighboring cells via cell surface molecules or junctions. Unlike epithelial cells, however, epithelioid cells make contacts over their entire surface, rather than at restricted portions. The term...
and myofibroblastoid properties including tight junctions, gap junctions, external laminae and contractility.
The perineurium is a smooth, transparent tubular membrane which may be easily separated from the fibers it encloses. In contrast, the epineurium
Epineurium
The epineurium is the outermost layer of connective tissue surrounding a peripheral nerve. It is made of dense irregular connective tissue and usually contains multiple nerve fascicles as well as blood vessels which supply the nerve...
is a tough and mechanically resistant tissue which is not easily penetrated by a needle.
See also
- Nerve fascicleNerve fascicleA small bundle of nerve fibers, enclosed by the perineurium, is called a funiculus; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or nerve fascicles, which are bound together in a common membranous...
- EndoneuriumEndoneuriumThe endoneurium, also referred to as an endoneurial channel, sheath or tube, is a layer of delicate connective tissue made up of endoneurial cells that encloses the myelin sheath of a spinal cord nerve fiber. These are bundled up into groups called nerve fascicles, which have a protective sheath...
- EpineuriumEpineuriumThe epineurium is the outermost layer of connective tissue surrounding a peripheral nerve. It is made of dense irregular connective tissue and usually contains multiple nerve fascicles as well as blood vessels which supply the nerve...
- Connective tissue in the peripheral nervous systemConnective tissue in the peripheral nervous systemA peripheral nerve contains two types of tissue: nerve fibers, and connective tissue. Dendrites and axons with schwann cells and myelin sheath are surrounded by connective tissue. A nerve fiber in the peripheral nervous system consists of an axon or long dendrite, myelin sheath and their schwann...
