Frequently Asked Questions about the Cranial Nerve Handout and Functional Components

Short Ciliary Nerves

On the cranial nerve handout, it says that the trigeminal nerve has GSA and SVE, with the SVE going throught the foramen ovale. Everything else is in black (GSA). I'm studying the opthalmic nerve (V1) right now, which is of course part of the trigeminal nerve, and according to the Netter online outlines, the short ciliary branches of the opthalmic nerve have parasympathetic and sympathtic fivers going to the ciliary body and iris. Shouldn't the short ciliary branches be SVE?
  • The short ciliary N contains:
    1. GSA fibers from the Nasociliary N (opthalmic N - V1) - pass through ganglion but do NOT synpase
    2. GVE fibers (parasympathetic) from Inferior branch of Oculomotor N (III) these fibers synpase in the Ciliary ganglion
    3. sympathetic fibers from Internal Carotid plexus - pass through ganglion but do NOT synpase (already post-gang. because synpased in Superior Cervical Ganglion)
  • I agree. I would go on to suggest that if Netter shows these hitchikers going to the "iris" then refine your knowledge. The sympathetic (GVE) hitchhikers are going to the pupil dilator and to parts of the conjuntiva. Thus, loss of the sympathetic root of the ciliary ganglion is expected to cause pupil constriction (unopposed pupil constricter innervated by parasympathetic postganglionic fibers having cell bodies in the ciliary ganglion) and counjunctivial injection to parts (near the cornea) of the conjunctiva (loss of vasculature tone).
  • The postganglionic parasympathetic fibers (GVE) go to the ciliary body to mediate accommodation (thickness of the lens) and to the pupil constricter to decrease the diameter of the pupil.
  • The native GSA fibers from ophthalmic nerve are providing touch, temperature, and pain sensation to the globe. In particular, these fibers are mediating pain to the cornea. Thus, the afferent limb of corneal blink reflex is mediated by GSA fibers in the short and long ciliary nerves. The efferent limb (the blink) is mediated by SVE fibers of the facial nerve.
  • The crux of the matter for you is that you, reasonably, conclude that a nerve should only contain native fibers (run the entire course of the nerve) and, thus, you insist that the GVE fibers in the short ciliary nerves be, instead, SVE fibers. It does not work that way. Notice that there are no GVE (blue) fibers in the trigeminal nerve that leave the brainstem. Nevertheless GVE postganglionic fibers follow distal trigeminal pathways. They are "hitchhikers" from the parasympathetic ganglia (the COPS) and from the superior cervical sympathetic trunk ganglion. These fibers carry out the activities defined by the GVE component. These activities are not native to the trigeminal nerve. Please accept this.

Mandibular Nerve and SVE component

I think it was stated in class, and in a book that the muscles of mastication were innervated by the mandibular division of the trigeminal nerve. My question was that on the cranial nerve handout, the muscles of mastication were shown as SVE, but the mandibular nerve was shown as GSA. How would muscles of mastication then be a branch of the mandibular nerve? Thank you.
  • The mandibular N (V3) has both GSA and SVE fibers. It is the only division of the trigeminal N (V) with both motor (SVE) and sensory (GSA).
    • Opthalmic N - V1 - GSA
    • Maxillary N - V2 - GSA
    • Mandibular N - V3 - GSA and SVE
  • Although I can not be certain, I think that this confusion stems from the drawing of the trigeminal nerve on the cranial nerve handout. You have somehow concluded that the handout shows the mandibular nerve as GSA only. Please take another look a the handout and focus on that small region between the foramen ovale and auriculotemporal nerve (notice that the auriculotemporal nerve is shown having two arms (they split around the middle meningeal artery).
  • The SVE (green) and GSA (black) lines are meant to represent functional components within the mandibular nerve. I suspect that you are looking at the handout and seeing two separate nerves coming out of the foramen ovale -- one green and one black. It might be helpful if you draw a tube to represent a common connective tissue sheath around the mandibular nerve as it exits the foramen ovale. Include both the green and the black line. Thus, you will have indicated that there is a single nerve, the mandibular nerve, exiting the foramen ovale and that within the mandibular nerve are two functional components - SVE and GSA.

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Topic revision: r1 - 19 Oct 2006, UnknownUser
 
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