Talk:Afferent nerve fiber
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Single long dendrite?
I'm concerned about the figure, which seems to suggest that sensory neurons from the skin typically terminate in the spinal column. As far as I am aware, the vast majority project to the brain, with the first connection occurring in the cuneate nucleus. 126.96.36.199 21:36, 11 July 2016 (UTC)
- I'm having a hard time getting a few things straight, concerning the nature of what makes up the body of afferent (sensory) nerves. The current text of this page says: "The structure of an afferent neuron contains a single long dendrite and a short axon". Presumably, this refers to a neuron the body of which is in the dorsal root ganglion. So presumably the nerve that carries the sensory signals from the skin, for instance, towards the spine is a bundle of those long dendrites. Is that right? That seems strange to me, not least because elsewhere it says that neurons have myelin sheaths around their axons - and doesn't mention the dendrites. I have seen no mention anywhere of myelin around dendrites. So if the afferent nerves are a bundle of dendrites, that means they have no myelin? But since myelin is there to speed up the impulses, doesn't that make afferent nerves slow? Otherwise, if the afferent nerves are bundles of axons, where are the neuron bodies? If they are in the dorsal ganglions, that would mean that the signal travels 'down' the axon, 'towards' the cell bodies... But that seems impossible. The other possible answer would be for the neuron bodies to be in the skin. But I don't see any references that say that. So I'm baffled. Could some one clear that up for me (and in the articles)? David Olivier 22:59, 28 June 2007 (UTC) UPDATE: I've found the answer to those questions: Pseudounipolar neuron. That kind of neuron has a "dendrite" that actually is (or is like) an axon, with myelin and all. I think some reference to that should be in the text at least on this page. David Olivier 17:25, 30 June 2007 (UTC)
Question 1. Is there a single long fiber that goes from the skin to the brain?
Answer: No. Sensory neurons make synaptic connections to spinal cord interneurons which, in turn, form myelinated fiber bundles that project to the brain.
Question 2. What is the anatomy of a sensory neuron?
Answer: Note this is a simplification, but in general... Sensory neurons have cell bodies in the dorsal root ganglion (see Figure-1). These neurons are considered pseudounipolar (see Figure-2). You can think of this unique subtype as consisting of just one long axon, that happens to have a cell body transit station smack-in-the-middle. That is, the axon starts at the skin, and is connected to some specialized sensor (now that might sound like a dendrite, so if it helps, just think of the sensor filling the role of the dendrite, so then you can keep thinking about axons in a familiar way... myelinated projections that send one-way electrical signals). Then whenever that sensor is activated, electrical signals rush towards the spine. It just happens that on their way, these impulses can briefly depolarize the cell body too. But basically they just keep flowing towards the spine. After the signal passes the soma it's back to being a dogmatic axon. Niubrad (talk) 10:26, 26 January 2018 (UTC)
Pain and Afferent Nerves
This publication gives insight on how non-peptidergic primary afferent neurons are involved in pain signaling: Saeed and Ribeiro-da-Silva Molecular Pain 2012, 8:64 Pain-related (nociceptive) information is carried from the periphery to the dorsal horn of the spinal cord mostly by two populations of small diameter primary afferents, the peptidergic and the non-peptidergic. The peptidergic population expresses neuropeptides, such as substance P and calcitonin gene-related peptide, while the non-peptidergic fibers are devoid of neuropeptides, express the purinergic receptor P2X3, and bind the isolectin B4. Pshuster (talk) 16:30, 16 December 2012 (UTC)
"The majority of these are unipolar neurons in that they have a single axon leaving the cell body and is sent towards the sensory organ." Don't most sorts of neurons have a single axon? Should it say "a single neurite"? Also "and is sent towards the sensory organ" is poor English. Better would be a new sentence "This axon/neurite extends towards the sensory organ". Also the paragraph before the one with this sentence says that afferent neurons are pseudounipolar, which agrees with the illustration. So which is it? Theodore.norvell (talk) 16:12, 11 November 2013 (UTC)
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