| Endoneurium | |
|---|---|
 Transverse section of humantibial nerve. | |
 Nerve structure | |
| Details | |
| Part of | myelin sheath ofnerves |
| System | Nervous system |
| Identifiers | |
| TA98 | A14.2.00.014 |
| TA2 | 6158 |
| FMA | 52586 |
| Anatomical terminology | |
Theendoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicateconnective tissue around themyelin sheath of each myelinatednerve fiber in theperipheral nervous system.[1] Its component cells are calledendoneurial cells.[2] The endoneuria with their enclosed nerve fibers are bundled into groups callednerve fascicles,[3] each fascicle within its own protective sheath called aperineurium.[3][4] In sufficiently large nerves multiple fascicles, each with itsblood supply and fatty tissue, may be bundled within yet another sheath, theepineurium.
The endoneurium contains a liquid known asendoneurial fluid, which contains littleprotein. In theperipheral nervous system the endoneurial fluid is notionally equivalent tocerebrospinal fluid in thecentral nervous system. Peripheral nerve injuries commonly release increased amounts of endoneurial fluid into surrounding tissues; these can be detected bymagnetic resonance neurography, thereby assisting in locating injuries to peripheral nerves.
The endoneurium runs longitudinally along the nerve fiber, but with discontinuities wheresepta pass inward from the innermost layer of the perineurium. It contains fine bundles offibrous connective tissue, primarilycollagen, embedded in a matrix ofground substance.[5] This structure serves to supportcapillaryblood vessels, arranged so as to form a network of elongated meshes. Similar structures occur around some nervous components elsewhere in the body, for example around theSchwann cells on the peripheral side of the transitional zone on theauditory nerve.[6]
