Cranial Nerve Anatomy Trivia Quiz

Answer: Glossopharyngeal Nerve

Hmm. . . A little tricky. The facial nerve canal (fallopian canal) is contained within the bone defining the middle ear space and is sometimes (about 25%) dehiscent, however, this is not typical. The nerve to the stapedius also isn't contained in the middle ear, it enters the muscle through a bony canal in the temporal bone. The facial nerve gives sensation to the tympanic membrane's EXTERNAL surface so that doesn't work either. Finally, the chorda tympani courses through the actual middle ear space and, although passing through the mucosa on its way out, is not contained within the mucosa for a substantial distance.

The vestibulocochlear nerve doesn't have branches in the middle ear space.

The vagus nerve, similar to the facial nerve, gives sensation to part of the EXTERNAL surface of the tympanic membrane and external auditory canal, but not the middle ear space. Note that the trigeminal nerve also contributes to EXTERNAL tympanic membrane sensation.

The glossopharyngeal nerve provides sensation to the INTERNAL surface of the tympanic membrane, and has parasympathetic efferent fibers contained in the mucosa that course over the promontory of the middle ear space to eventually supply secretomotor fibers to the parotid gland (Jacobsen's nerve).

Extra credit: Which nerve(s) supplies sensation and secretomotor innervation to the mucosa of the middle ear space?

Answer: Facial Nerve

First off, where the heck it the pterygoid canal? It's the bony canal that runs anteriorly in the sphenoid bone. It ends in the pterygopalatine fossa behind the pterygoid plates of the sphenoid bone. When the sphenoid sinus is well pneumatized, there will often be a space between the maxillary division of the trigeminal nerve and the nerve of the pterygoid canal as the pneumatization extends toward the pterygoid plates. Both of these nerves run in the lateral wall of the sphenoid sinus and are best recognized on coronal CT scans of the sinuses.

The actual nerve of the pterygoid canal consists of two types of fibers. The first is preganglionic parasympathetic fibers. These project from the superior salivatory nucleus of the medulla, and travel in the nervus intermedius of the facial nerve in the internal auditory canal. After passing through the geniculate ganglion these fibers become the greater petrosal nerve (or greater superficial petrosal nerve).

The greater petrosal nerve then joins the second type of fibers in the nerve of the pterygoid canal. These are sympathetic fibers from the carotid plexus (from deep petrosal nerve). These two types of fibers then form the nerve of the pterygoid canal (Vidian nerve).

The nerve of the pterygoid canal continues on to the pterygopalatine ganglion where the preganglionic parasympathetic fibers synapse and cell bodies are located. (Obviously the sympathetic fibers cruise on through this ganglion.) Postganglionic fibers then supply the lacrimal gland and the mucous glands in the mucosa of the nasal and oral cavities.

Extra credit: What does the root "pterygoid" mean and who was Vidian?

Answer: Palatoglossus

Palatoglossus is innervated by the vagus nerve via its pharyngeal branch. The rest of the muscles are indeed innervated by the hypoglossal nerve. The hypoglossal nerve also innervates all of the intrinsic musculature of the tongue.

Extra credit: What does the ansa hypoglossi nerve do?

Answer: Trigeminal and Oculomotor Nerves

WOW, another ganglion question, but don't you just love the parasympathetic nervous system? The ciliary ganglion contains fibers of the short ciliary nerves (ophthalmic division of the trigeminal nerve) from the eye. These fibers don't synapse in the ganglion, rather they're just passin' through. The ciliary ganglion also contains the cell bodies of parasympathetic nerves from the oculomotor nerve (that's why it's a ganglion after all). Post-ganglionic branches innervate the eye's ciliary body and the constrictor pupillae muscle.

Extra credit: Which cranial nerves are involved in the blink reflex?

Answer: Foramen Magnum

The key word here is ENTER. The accesory nerve is all motor, so it's pretty much a one way tract out to the muscles. Don't forget about the spinal component of this nerve from C1-C5 (and possibly C6) that enters the posterior cranial fossa via the foramen magnum, posterior to the vertebral artery.

Once intracranial and all joined up, the accesory nerve leaves the posterior cranial fossa through the jugular foramen (with the glossopharyngeal and vagus nerves).

Extra credit: Which part of the jugular foramen does the accesory nerve exit through and what's its usual relationship to the jugular vein?

Answer: Optic Nerve

The cavernous sinus or its wall contains the oculomotor nerve, the ophthalmic and maxillary divisions of the trigeminal nerve, and the abducens nerve. The optic nerve is not within the wall or the cavernous sinus itself.

Most people I've met disagree about which nerves are in the wall versus the sinus itself, so I won't go there.

Extra credit: What other important structure is within the cavernous sinus?

Answer: The Superior Vestibular Nerve

The macula of the utricle detects linear acceleration in the horizontal plane. (As opposed to the saccule which detects vertical acceleration). The superior vestibular nerve innervates this structure as well as the superior and lateral semi-circular canals, and a little part of the saccule.

The rest of the vestibular apparatus - the posterior semi-circular canal and the main portion of the saccule - is supplied by the inferior vestibular nerve.

Testing the function of different portions of the vestibular system (mainly the horizontal canal) can help us determine which if a vestibular schwannoma (a benign tumor also known as an acoustic neuroma) is on the superior or inferior division of the vestibular nerve within the internal auditory canal.

Extra credit: Which division is more prone to vestibular schwannomas, the superior or inferior vestibular nerve?

Answer: Olfactory Nerve

According to the official Nobel website:

In 2004, Richard Axel and Linda B. Buckfor were awarded the prize "for their discoveries of odorant receptors and the organization of the olfactory system"

Robert Bárány got the prize in 1914 "for his study of the vestibular apparatus." In 1961 Georg Von Bekesy got one "for his discoveries of the physical mechanism of stimulation within the cochlea."

Ragnar Granit, Haldan Keffer Hartline, and George Wald got the prize in 1967 for "for their discoveries concerning the primary physiological and chemical visual processes in the eye"

I guess taste is up next :)

Extra credit: Which three (yes three) nerves carry special sensory taste fibers?

Answer: Inferior Vagal Ganglion

I know this is cranial nerve minutia, but those realizing that these cell bodies are located peripherally will have recognized only one ganglion was in the list. Here's my brief explanation of the sensory pathways involved.

The general sensory (i.e. pain, touch, and temperature) fibers from the vocal folds and subglottis accompany the recurrent laryngeal nerve. This nerve exits the larynx at the cricothyroid joint and descends in the neck. It courses behind the aorta (left) or subclavian (right) and then ascends to the inferior vagal ganglion where the cell bodies are located. Some may also go to the superior vagal ganglion.

Supraglottic sensation is similar and is via the superior laryngeal nerve which exits the larynx at the thyrohyoid membrane. Cell bodies for these general sensory nerves are also found mainly in the inferior vagal ganglion (although some may be found in the superior vagal ganglion too). The superior vagal ganglion is mainly somatic sensory nerve cell bodies for the auricular nerve.

The other end of the somatic sensory nerves in the inferior and superior vagal ganglion project centrally to the spinal trigeminal tract nucleus.

Visceral sensory information from the larynx goes in the same route, to the inferior vagal ganglion where the cell bodies reside. The vagus innervates some serious viscera (all the way to the left splenic flexure). Obviously then visceral input from this nerve, although we're not really aware of it, is quite important. These nerves project from the inferior vagal ganglion to the caudal portion of the nucleus of the tractus solitarius in the medulla. Some may also go to the dorsal vagal nucleus.

The dorsal vagal nucleus is mainly a central motor nucleus for smooth muscle and glands of the pharynx, larynx, thorax and abdominal viscera.

Extra credit: What does the nucleus ambiguus do?

Answer: Abducens Nerve

In its long trek to get peripheral and become a real nerve, the little abducens nerve goes through some canyons, lakes, and tunnels. One of the canyons is Dorello's canal. This bow shaped gap is formed by the petrous portion of the temporal bone and the clivus.

The abducens nerve then goes on to a big lake known as the cavernous sinus.

Extra credit: What other obstacles are waiting for our little hero on his way to the lateral rectus muscle?