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Question about cranial nerves (regarding terminal nerve)

*Hemidactylus* hemidactylus at my-deja.com
Mon Dec 6 01:28:41 EST 1999

In article <82e9cb$oqq$2 at oravannahka.helsinki.fi>,
  dag.stenberg at helsinki.nospam.fi wrote:
> c_thomas_wild at my-deja.com wrote:
> > There are only 12 pairs of cranial nerves in a human being.
> And in vertebrates, my Zigmond et al. tells me.
> > If one
> > were to add a 13th, it could be the reticular formation of the brain
> > stem (the RAS and RIS/Reticular Activating System-Reticular Inhibiting
> > System) which regulates the ability to pay attention.  The reticular
> > formation is closely associated with being awake/being
> > asleep/consciousness and in many ways is the essence of life itself.
> > The reticular formation is associated with a number of different
> > neurological challenges including petit mal, absence, and the
> > ADHD/ADD/Hyperactivity syndrome.  The 12 pairs of cranial nerves tend
> > to plug into the reticular formation of the brain stem so to speak, as
> > I recall.
> Don't. The reticular formation of the brain stem is a complex set of
> nuclei and connections, some with very specific functions. It is
> absolutely not an entity, and calling it a 13th cranial nerve just
> confuses things.

There is a terminal nerve which (as I recall) bears the odd designation of
cranial nerve 0. I think it is developed in elasmobranchs but its been a
while since I've read up on this subject.

> The "13th" that Sarah's professor admitted to having heard of but not
> being able to recall the name of, might of course well be the
> vomeronasal organ.

This would likely open the issues concerning humans and pheromones. The VNO
and terminal nerve could very well be homologous, but I'm not too sure off
the top of my head.

My comparative anatomy book (Kent and Miller's _Comparative Anatomy of the
Vertbrates_, p. 405) discusses the terminal nerve as being "without a
numerical designation", but I recall the cranial nerve 0 designation from
somewhere. There's probably some variance in texts on treatment or ignorance
of this nerve. It's probably too trivial to be covered in human anatomy
references. I guess the terminal weighs in as the elusive or phantom 13th
nerve, though (even the number gives it an eery persona).


Kent GC and Miller L. 1997. Comparative Anatomy of the Vertebrates. Wm. C.
Brown Publishers. Dubuque

Scott Chase

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