Why are special visceral efferent nerves are named as such?

  1. They are supplying motor impulses to muscles of pharyngeal arch, which are both skeletal(facial) and visceral(laryngeal) 1, so why only visceral in name?

  2. Why the name special?

I tried wikipedia but didn't find any information.

  • $\begingroup$ What nerves are you referring to specifically as special visceral efferent? The link you include only has the text "special visceral efferent" once that I can find, in the table at the top. $\endgroup$ – kmm Aug 10 '17 at 23:17
  • $\begingroup$ @kmm 5, 7 ,9 , 10 and 11c most probably. $\endgroup$ – Anubhav Goel Aug 10 '17 at 23:35
  • $\begingroup$ I find this ncbi.nlm.nih.gov/pubmed/8109195 suggesting to change the terminology. $\endgroup$ – JM97 Sep 7 '17 at 14:29

1.They are supplying motor impulses to muscles of pharyngeal arch, which are both skeletal(facial) and visceral(laryngeal), so why only visceral in name?

Visceral is a derivative of the word viscus, which simply means "an internal organ of the body". I believe visceral is being used with this, more general, connotation.

2.Why the name special?

The word special is used because SVE nerves are involved with what are considered to be special senses, which is to say, senses that have "specialized" organs (and subsequently, "special" nerves) devoted to them. The special senses are: vision, hearing (and balance), smell, and taste.

To quote Wiki:

The distinction between special and general senses is used to classify nerve fibers running to and from the central nervous system – information from special senses is carried in special somatic afferents and special visceral afferents. In contrast, the other sense, touch, is a somatic sense which does not have a specialized organ but comes from all over the body, most noticeably the skin but also the internal organs (viscera). Touch includes mechanoreception (pressure, vibration and proprioception), pain (nociception) and heat (thermoception), and such information is carried in general somatic afferents and general visceral afferents.

Although this passage mentions afferents, (I'm fairly certain that) the usage of "special" regarding efferents carries the same meaning.

  • $\begingroup$ Special was used for special senses is absolutely correct. But, only for afferent. These are special senses , meaning sensory. These prove nothing for efferent. Else, there would be no GSE. These muscle supply special organ eye, dont they? $\endgroup$ – Anubhav Goel Aug 10 '17 at 22:59
  • $\begingroup$ GVE are aiding special senses as well. $\endgroup$ – Anubhav Goel Aug 10 '17 at 22:59
  • $\begingroup$ @AnubhavGoel If special only applies to afferent nerves then how can the OP be asking about SVE? Special Visceral Efferents $\endgroup$ – Charles Aug 10 '17 at 23:06

Why they are special?

They are also called Branchial efferent. They are special because they supply striated muscles derived from Branchial arches. https://en.m.wikipedia.org/wiki/Special_visceral_efferent

Like Mandibular nerve, nerve of 1st arch supply muscles of mastication and motor nuclei of facial nerve, 2nd arch, supply facial muscles and Stylohyoid.

Special Visceral Efferent (SVE) These fibres innervate certain striated muscles with a special embryological origin. They are referred to as the branchiomeric muscles. Structures that develop into gill arches in fish develop instead into various structures near or in the head and neck (muscles of the face, larynx and pharynx). Although these muscles are identical to normal striated muscle, neurons for branchiomeric muscles have a distinctive location in the brainstem.


Why only visceral?

This term is quite ambiguous. That's why some scientists prefer term Branchial efferents. https://en.m.wikipedia.org/wiki/Special_visceral_efferent

The nerves supply striated muscles(also called skeletal, though most facial muscles have no skeletal support).

These do not supply any smooth muscle of viscera (laryngeal muscles are striated too).

But, still they are called visceral. Well, that is because the muscles supplied are actually mostly to various viscera. Larynx is a viscera. Pharynx and palate are viscera too. All these are supplied by 5 , 9 and 10th nerve.(Nuclei - motor nuclei of 5th, Nucleus ambiguus for 9 and 10th) Nerve to stapedius is muscle of middle ear, again a sensory organ.

So, the word viscera was added.

Facial muscles and sternocleidomastoid and trapezius are of course not supplying organs(viscera). That is why some say branchial efferent to remove ambiguity. Branchial efferent represents muscles derived from branchial/pharyngeal arches. That's what is important about these nuclei.

  • $\begingroup$ I'm having a difficult time finding meaning in your explanation of why "special" is used..according to your answer, you say, "*They are special because they supply striated muscles derived from Branchial arches". My question is, why does that then require the usage of "special"? Or, what aspect of that is described by using the term "special"? Im not seeing the logical connection. Thanks. $\endgroup$ – Charles Aug 10 '17 at 20:37
  • $\begingroup$ @Charles I dont know of text for sure. But, that is what are proffessors at college told us. $\endgroup$ – Anubhav Goel Aug 10 '17 at 22:32
  • $\begingroup$ I see.. well, in the case, I believe that special has a very specific meaning, of which is being used to classify organs and nerves based on if an organ has to interact with another organ to perform a task, and by extension, whether or not the nerves of those organs run directly to the spinal cord or not. $\endgroup$ – Charles Aug 10 '17 at 22:44

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