Supporting cells of the nervous system

[sameeralord]

Hello everyone,

I have a quick question. Ok the endoneurium is a layer of delicate connective tissue that encloses the myelin sheath of a nerve fiber within a fasciculus. Now my question is supporting cells of the nervous system like glial cells usually connect two nerve fibres together, so do they lie outside the endoneurium? Thanks

 

[bobze]

Hello everyone,

I have a quick question. Ok the endoneurium is a layer of delicate connective tissue that encloses the myelin sheath of a nerve fiber within a fasciculus. Now my question is supporting cells of the nervous system like glial cells usually connect two nerve fibres together, so do they lie outside the endoneurium? Thanks

A never fiber is a single axon, either myelinated by an oligodendrocyte (CNS) or Schwann cell (PNS). In the CNS oligodendrocytes can myelinate multiple axons, while in the PNS a Schwann cell will only myelinate a single axon. In the PNS however, Schwann cells can ensheath (not myelin) multiple smaller diameter axons, but this is not the same as myelinating them.

A single nerve fiber (myelin+axon) doesn't have an endoneurium. A nerve^*** (a collection of nerve fibers), just the cytoplasm of the axon and wrapped plasma membranes of enmyelinating cell.

So a collection of nerve fibers in a nerve will have a perineurium around the outside (which is a special cellular layer derived from fibroblasts). The inside part, holding all those nerve fibers in the nerve will be the endoneurium. Which will be composed of fibroblasts, macrophages, supportive cells derived from the neural crest (satellite cells→glial cells)-- Oligodendrocytes (special type of glial cell), collagen type III (reticular fibers) and small capillaries (in larger nerves).

Epineurium then, is only found around very large nerves which contain lots of smaller nerves and has blood vessels and often times adipose around it.


^***Be aware that many texts or people you encounter will reserve "fasciculus" for a structural layer of muscle and will not call a collection of nerve fibers a fasciculus, rather a nerve. And will also call a collection of nerves, a nerve (just to make it real hard on you )

 

[nismaratwork]

Mmmm.. sameeralord, bobze hit this one out of the park, but I don't suppose you have any further interest in the role of these supporting cells (especially glial cells) which is being uncovered? I find the potential role of glial cells in drug resistance more than fascinating... off topic though, and I won't venture there without your blessing.

 

[sameeralord]

A never fiber is a single axon, either myelinated by an oligodendrocyte (CNS) or Schwann cell (PNS). In the CNS oligodendrocytes can myelinate multiple axons, while in the PNS a Schwann cell will only myelinate a single axon. In the PNS however, Schwann cells can ensheath (not myelin) multiple smaller diameter axons, but this is not the same as myelinating them.

A single nerve fiber (myelin+axon) doesn't have an endoneurium. A nerve^*** (a collection of nerve fibers), just the cytoplasm of the axon and wrapped plasma membranes of enmyelinating cell.

So a collection of nerve fibers in a nerve will have a perineurium around the outside (which is a special cellular layer derived from fibroblasts). The inside part, holding all those nerve fibers in the nerve will be the endoneurium. Which will be composed of fibroblasts, macrophages, supportive cells derived from the neural crest (satellite cells→glial cells)-- Oligodendrocytes (special type of glial cell), collagen type III (reticular fibers) and small capillaries (in larger nerves).

Epineurium then, is only found around very large nerves which contain lots of smaller nerves and has blood vessels and often times adipose around it.


^***Be aware that many texts or people you encounter will reserve "fasciculus" for a structural layer of muscle and will not call a collection of nerve fibers a fasciculus, rather a nerve. And will also call a collection of nerves, a nerve (just to make it real hard on you )

Thanks a lot for understanding my question and clearing my misconception. Great answer

@nismaratwork: You are more than welcome to share your knowledge on Glial cells.