jimmydasaint Posted October 8, 2010 Share Posted October 8, 2010 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. Link to comment Share on other sites More sharing options...
Glider Posted October 9, 2010 Share Posted October 9, 2010 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. 1 Link to comment Share on other sites More sharing options...
Ahsan Iqbal Posted January 11, 2011 Share Posted January 11, 2011 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. Link to comment Share on other sites More sharing options...
lemur Posted January 11, 2011 Share Posted January 11, 2011 related question: does myelin increase the signal-speed of nerves? Does it determine it? Link to comment Share on other sites More sharing options...
Ahsan Iqbal Posted January 11, 2011 Share Posted January 11, 2011 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. Link to comment Share on other sites More sharing options...
granpa Posted January 11, 2011 Share Posted January 11, 2011 (edited) 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 Link to comment Share on other sites More sharing options...
Ahsan Iqbal Posted January 12, 2011 Share Posted January 12, 2011 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. Link to comment Share on other sites More sharing options...
megna73 Posted February 24, 2011 Share Posted February 24, 2011 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 Link to comment Share on other sites More sharing options...
jimmydasaint Posted April 11, 2011 Author Share Posted April 11, 2011 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 Link to comment Share on other sites More sharing options...
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