Which Human Neurons Have Myelin Around Them?

[jimmydasaint]

Surprisingly, I have been unable to find a clear answer to the OP question from the Internet. And I need to know which neurons have myelin around them specifically and which do not. Any replies, references to reviews or papers welcomed.

[Glider]

All neurons are myelinated with the single exception of C fibres. These are very small diameter 'primary afferent' polymodal fibres associated with detection of temperature change, noxious cold and noxious heat. Along with A-Delta fibres, C fibres are often called 'pain fibres' (C fibres are associated specifically with 'slow pain'; the burning, aching and diffuse pain that comes after some trauma. Being small diameter and non-myelinated, they have very slow conduction rates, about 0.5 to 2m per second, compared to say, large, myelinated motor neurons which conduct at around 300 - 400 metres per second. We could not function if all central nervous system neurons conducted at that rate. It would give us a reaction time in excess of 2 seconds as opposed to the average human reaction time of 500ms (that would select us out of the competition very quickly).

 

All CNS (central nervous system, i.e. brain and spinal cord) fibres are myelinated. The only difference between myelination in the CNS and the PNS (peripheral nervous system) is the type of cell responsible for myelination. In the PNS these are Schwann cells. Each of these wraps around and insulates a short length (about 1mm) of a single axon. In the CNS, oligodendrocytes provide myelination. These cells project to and wrap a portion of several axons so they also provide a kind of '3D scaffolding' as well as myelination.

 

Multiple Sclerosis (MS) is a progressive de-myelinating disease and provides a good example of what happens when neurons (other than C fibres) begin to lose myelination.

 

Information on myelination can be found in any introductory books on Human Biology, Psychobiology, Cognitive Neurosciences or Neurology.

[Ahsan Iqbal]

As a general rule, nerve fibers that are within the central nervous system are non-myelinated while those that form the peripheral nervous system may or may not be myelinated. The larger ones are generally myelinated while the smaller ones are not.

[lemur]

related question: does myelin increase the signal-speed of nerves? Does it determine it?

[Ahsan Iqbal]

related question: does myelin increase the signal-speed of nerves? Does it determine it?

 

Yes it does increase the speed of conduction in nerve fibers. The mechanism by whiuch it happens is known as saltatory conduction.

[granpa]

http://en.wikipedia.org/wiki/Repeater

 

http://www.physicsforums.com/showthread.php?p=1897203#post1897203

 

http://www.physicsforums.com/showthread.php?p=1897496#post1897496

Edited January 11, 2011 by granpa

[Ahsan Iqbal]

http://en.wikipedia.org/wiki/Repeater

 

http://www.physicsfo...203#post1897203

 

http://www.physicsfo...496#post1897496

 

I am not a moderator but I must say that a little introduction should have provided as to explain what are these links about.

[megna73]

What exactly is myelin? Myelin is a concentrically laminated membrane structure surrounding an axon around which lamellae (or cellular protrusions) repeat radially at a period of about 12 nm (Waxman, Kocsis & Stys 1995; Sherman & Brophy 2005). The myelin lamella is formed by fusion of the apposed inner leaflets of the plasma membrane in glial cells, with no intervening cytoplasm

 

 

spinal stenosis

[jimmydasaint]

As a general rule, nerve fibers that are within the central nervous system are non-myelinated while those that form the peripheral nervous system may or may not be myelinated. The larger ones are generally myelinated while the smaller ones are not.

 

Have you read what Glider said:

 

All CNS (central nervous system, i.e. brain and spinal cord) fibres are myelinated. The only difference between myelination in the CNS and the PNS (peripheral nervous system) is the type of cell responsible for myelination. In the PNS these are Schwann cells. Each of these wraps around and insulates a short length (about 1mm) of a single axon. In the CNS, oligodendrocytes provide myelination. These cells project to and wrap a portion of several axons so they also provide a kind of '3D scaffolding' as well as myelination.

 

With respect to you, I think I will follow Glider's comments