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Home Q & A Board Science-Related Homework Help High School Level Science
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johntdlemon johntdlemon
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11 years ago Edited: 11 years ago, johntdlemon
Hi, I'm new here. Slight Smile
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!
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#1
11 years ago
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 Slight Smile
wrote...
#2
11 years ago
I've never heard of myelin surrounding anything else but the axon, so I'm guessing it's only the axon that is affected.
Biology - The only science where multiplication and division mean the same thing.
johntdlemon Author
wrote...
#3
11 years ago
Thanks for your help! Slight Smile
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!
wrote...
#4
11 years ago
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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