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Title: Myelin sheaths only exist on axons? Post by: johntdlemon on Dec 8, 2012 Hi, I'm new here. :)
I did this question which asked if myelin sheaths only exist on axons, and the answer is no. I searched for this online, and most of the websites I found says otherwise. Wikipedia says:"Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin sheath, usually around only the axon of a neuron." Does this means myelin sheaths surround stuff other than axons? I know Wikipedia is not the most trusty source, but still... please help! I've run into a lot of faulty problems while doing the test-bank, so this question could easily be one of them. Thanks! Title: Re: Myelin sheaths only exist on axons? Post by: xihoney_3 on Dec 8, 2012 Myeline sheath is a covering that protects ever fiber and facilitates the speed of impulse conduction. Both axons and dendrites may or may not have myelin sheath. Most axons leaving the CNS are heavily myelinated with Schwann cells. Gaps in myeline sheath are termed nodes of Ranvier. Gerontologic considerations- myeline sheath degeneration; decreased nerve conduction
Hope this helps :) Title: Re: Myelin sheaths only exist on axons? Post by: savio on Dec 8, 2012 I've never heard of myelin surrounding anything else but the axon, so I'm guessing it's only the axon that is affected.
Title: Re: Myelin sheaths only exist on axons? Post by: johntdlemon on Dec 8, 2012 Thanks for your help! :)
I just found something that might be the cause of the confusion I'm having: the pseudounipolar neurons. Some say the pseudounipolar neurons have "two axons and no dendrites", while others consider the single nerve fiber as axon and dendrite fused together Quote from Human Physiology Pseudounipolar neurons have a single short process that branches like a T to form a pair of longer processes. They are called pseudounipolar (from the Late Latin pseudo = false) because, although they originate with two processes, during early embryonic development their two processes converge and partially fuse. Sensory neurons are pseudounipolar—one of the branched processes receives sensory stimuli and produces nerve impulses; the other delivers these impulses to synapses within the brain or spinal cord. Anatomically, the part of the process that conducts impulses toward the cell body can be considered a dendrite, and the part that conducts impulses away from the cell body can be considered an axon. Functionally, however, the branched process behaves as a single, long axon that continuously conducts action potentials (nerve impulses). Only the small projections at the receptive end of the process function as typical dendrites, conducting graded electrochemical impulses rather than action potentials. Quote from Wikipedia By definition, a pseudounipolar neuron has one axon with two branches: central and peripheral. These axonal branches should not be confused with dendrites. Pseudounipolar neurons do not have dendrites. Is there no consensus on this? Is this the reason why some say myelin sheaths do not surround specifically axons? Sorry for the delayed extra question. Thanks! Title: Re: Myelin sheaths only exist on axons? Post by: koreankougar on Dec 10, 2012 In science, there's always a special clause somewhere. If anything, I believe the wording is just a precaution so as to not claim a false fact that may be disproved in the future.
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