| Perineurium | |
|---|---|
 Transverse section of humantibial nerve (perineurium labeled at upper right) | |
 Nerve structure | |
| Identifiers | |
| TA98 | A14.2.00.015 |
| TA2 | 6156 |
| FMA | 52585 |
| Anatomical terminology | |
Theperineurium is a protective sheath that surrounds anerve fascicle.[1] This bundles togetheraxons targeting the same anatomical location.[1] The perineurium is composed fromfibroblasts.[2]
In theperipheral nervous system, themyelin sheath of each axon in a nerve is wrapped in a delicate protective sheath known as theendoneurium. Fascicles, bundles ofneurons, are surrounded by the perineurium. Several fascicles may be in turn bundled together with ablood supply andfatty tissue within yet another sheath, theepineurium. This grouping structure is analogous to the muscular organization system ofepimysium,perimysium andendomysium.
The perineurium is composed ofconnective tissue, which has a distinctlylamellar arrangement consisting of one to severalconcentric layers. The perineurium is composed of perineurial cells, which areepithelioidmyofibroblasts. Perineurial cells are sometimes referred to asmyoepithelioid due to theirepithelioid andmyofibroblastoid properties includingtight junctions,gap junctions,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.
The perineurium, as the epineurium, has a clinical importance following a trauma, like a fracture. A sort of lesion calledaxonotmesis[3] 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.
