Cranial Nerve Review

Question 1

What are the parasympathetic targets in the head?

Answer 1

include constrictor pupillae and ciliary smooth muscles, submandibular, parotid and sublingual salivary glands (and other minor salivary glands), mucous glands of the nasal cavity and hard palate, lacrimal glands, and glands of the pharynx, larynx and esophagus.

Question 2

Which three CN carry parasympathetics to the head?

Answer 2

3, 7, and 9

Question 3

Preganglionic cell bodies of CN III GVE parasympathetic fibers are located where?

Answer 3

midbrain (7 is in the pons and 9 and 10 are in the medulla)

Question 4

Describe the course of the chorda tympani branch of CN VII

Answer 4

The chorda tympani nerve of CN VII , carries preganglionic parasympathetic fibers (and also taste fibers). The preganglionic cell bodies are located in the brainstem motor nuclei of CN VII. The preganglionic fibers enter the facial canal, bypassing the geniculate ganglion, before entering a separate canal in the bone which conducts it to the middle ear (tympanic cavity). The nerve passes over the medial surface of the tympanic membrane, arches across the malleus, and leaves the tympanic cavity near the anterior border of the membrane and exits the skull via the petrotympanic fissure.

The chorda tympani nerve joins the lingual nerve (sensory branch of V3 (GSA)) high in the infratemporal fossa, and hitchhikes along with that nerve to the submandibular ganglion, where synapses are formed with postganglionic parasympathetic cell bodies.
Postganglionic parasympathetic fibers then leave the submandibular ganglion and travel to the submandibular gland or rejoin the lingual nerve to reach the sublingual gland.

Question 5

GVE sympathetics to the sublingual and submandibular glands hitchhike from where?

Answer 5

lingual and facial arteries

Question 6

The SA component of chorda tympani does what and cell bodies where?

Answer 6

anterior 2/3s of the tongue. The cell bodies of taste neurons are located in the geniculate ganglion in the genu of the facial canal

Question 7

Describe the course of the lesser petrosal n.

Answer 7

Preganglionic fibers from CN IX that are destined for the parotid gland exit the skull along with the rest of CN IX via the jugular foramen. These fibers join the tympanic nerve and ascend to the tympanic cavity through a canal in the bone separating the carotid canal and jugular foramen. This is sometimes called the tympanic cannaliculus.
Preganglionic parasympathetic fibers continue beyond the middle ear plexus as the lesser petrosal nerve. This is just a name change.
The lesser petrosal nerve passes forward through the petrous part of the temporal bone and emerges through the hiatus of the lesser petrosal nerve onto the floor of middle cranial cavity. It crosses floor of the middle cranial fossa in the groove of the lesser petrosal nerve, then exits the skull via foramen ovale (with V3) to reach in the otic ganglion in the infratemporal fossa where synapses are formed with postganglionic parasympathetic cell bodies.

Postganglionic fibers distribute to the parotid gland by hitchhiking on the auriculotemporal nerve (another sensory branch of V3 (GSA)), which provides GSA to parotid capsule (among other things).

Note: The tympanic nerve is also carrying GSA fibers to the middle ear and auditory tube

Question 8

What two nerves combine to form he nerve of the pterygoid canal?

Answer 8

deep and greater petrosal nn.

Question 9

Parasympathetic innervation of the ciliary and constrictor pupillae smooth muscles of the eye is via which CN nerve?

Answer 9

III

Question 10

Describe GVE parasympathetics to the eyeball

Answer 10

Preganglionic parasympathetic fibers from CN III that are destined to innervate these smooth muscles have their cell bodies in the brainstem motor nuclei of CN III. These preganglionic parasympathetic fibers exit the cranial cavity via the superior orbital fissure along with the rest of cranial nerve III.

These fibers enter the orbit and reach the ciliary ganglion via the parasympathetic motor root of III (shown in green). Within the ciliary ganglion, synapses are formed with postganglionic parasympathetic cell bodies.

Postganglionic parasympathetic fibers (shown in orange) exit the ganglia and hitchhike along the short ciliary nerves (sensory branches of V1 (GSA)) to reach their targets.

Question 11

What fibers do the short ciliary n. carry?

Answer 11

GVE postganglionic para and sympathetics and GSA fibers

Question 12

GVE sympathetics in the eye do what?

Answer 12

innervate two other smooth muscles of the eye, the dilator pupillae and the superior tarsal muscle.

Question 13

What are the sympathetic targets of the head?

Answer 13

sweat glands, vascular smooth muscle and two smooth muscles of the eye: the superior tarsal muscle and the dilator pupillae muscle

Question 14

Describe sympathetic innervation to the head

Answer 14

Preganglionic sympathetic fibers destined for the head arise from spinal cord segments T1‐T2. Pre‐ ganglionic cell bodies are located in the spinal cord gray matter (lateral horn) of these segments. The preganglionic axons exit the spinal cord via the T1 & T2 spinal nerves to reach the sympathetic trunk. These fibers then ascend in the sympathetic trunk to reach the superior cervical chain ganglion where they synapse with the postganglionic neurons. Postganglionic fibers exit the sympathetic chain and form the carotid peri‐arterial plexus which surrounds the internal and external carotid arteries and their branches to reach their targets in the head.

Note that most (>95%) of these fibers do not travel with cranial nerves.

Question 15

What nn. carry sympathetics do travel with CNs?

Answer 15

Exceptions are the sympathetic fibers found in the deep petrosal nerve and in the nasociliary, short ciliary & long ciliary nerves

Question 16

Where are the cell bodies of CN I?

Answer 16

CN I is responsible for our sense of smell. It exits the skull via the cribriform foramina in the anterior cranial fossa. Note that the SA cell bodies are not organized into a peripheral sensory ganglia, rather they are diffusely distributed along the olfactory epithelium

Question 17

Where are the cell bodies of CN II?

Answer 17

CN II is responsible for our sense of sight. It exits the skull via the optic canal in the middle cranial fossa. Note that the SA cell bodies are not organized into a peripheral sensory ganglia, rather they are diffusely distributed in the retina

Question 18

Where are the cell bodies of CN VIII?

Answer 18

CN VIII is responsible for audition and equilibrium. It exits the skull via the internal acoustic meatus in the posterior cranial fossa. Note that the SA cell bodies are found in the spiral and vestibular ganglia.

Question 19

Lesion of CN XII would cause what?

Answer 19

To test nerve function, the patient is asked to stick out their tongue. If the nerve is lesioned, the tongue will deviate to the affected side

Question 20

What kinds of fibers does CN III carry?

Answer 20

GSE and GVE para

Question 21

The superior branch of CN III innervates what?

Answer 21

the levator palpebrae superioris and the superior rectus muscles.

Question 22

The inferior branch of CN III innervates what?

Answer 22

the medial rectus, inferior rectus and inferior oblique muscles

Question 23

Lesion of CN III would cause what?

Answer 23

Loss of parasympathetic innervation to the sphinchter pupillae muscle will result in a dilated pupil with loss of the light reflex on the affected side. Loss of motor innervation to mutiple extraocular muscles results in severe ptosis (levator palpebrae supeioris), diplopia, external stabismus (eye moves down and out at rest due to unopposed CN IV and VI), and loss of parallel gaze

The easiest clinical test is the pupillary light test.

Question 24

The ciliary ganglion is attached to which branch of CN III?

Answer 24

inferior

Question 25

Spit and tears come from what kind of innervation?

Answer 25

GVE parasympathetics from CN VII

Question 26

How do you test for a CN VII lesion?

Answer 26

Easy clinical tests for CN VII function are asking the patient to smile or raise their eyebrows.

Question 27

Lesion of CN IX would present as what?

Answer 27

the absence of the gag reflex (sensory IX, motor X), along with a dry mouth due to loss of innervation of the parotid salivary gland

Question 28

Clinical test for CN IX lesion

Answer 28

Clinical test for the integrity of CN IX is to stimulate the gag reflex. Absence of the gag reflex can be explained by loss of either IX or X, so further testing would be required. One discriminator would be the presence of absence of dry mouth

Question 29

Lesion of CN X would present as what?

Answer 29

difficulty swallowing (or dysphagia) due to loss of innervation of pharnygeal muscles, hoarseness or paralyzation of the vocal fold due to loss of innervation of laryngeal muscles, loss of gag reflex, loss of cough reflex, drooping palate and displacement of the uvula away from the side of the lesion

Question 30

Clinical test for CN X lesion

Answer 30

Clinical tests would include listening to the patient’s speech, evaluation of swallowing, testing the gag reflex,and examination of the uvula by having the patient say “Ahh”