CNn. IX, X, XI, XII

Question 1

Where does CN IX exit the brain stem and the cranial vault?

Answer 1

Exits the brainstem at the post-olivary sulcus as the most rostral of the cranial nerves which exit here.

Exits the cranial vault through the jugular foramen.

Question 2

What two external ganglia are associated with CN IX, where are they located, and what do they mediate?

Answer 2

The inferior (petrosal) and superior (jugular) glossopharyngeal ganglia are located at the jugular foramen.

These ganglia will mediate general, visceral, and special sensations.

Question 3

Describe where the cell bodies of primary afferents conducting GVA of CN IX lie and where they peripherally and centrally project.

Answer 3

Primary sensory neurons of GVA lie in the inferior (petrosal) glossopharyngeal ganglia.
Peripherally project to the carotid body and carotid sinus.
Centrally project to the most caudal solitary nucleus via the solitary tract.

Question 4

Describe where the cell bodies of secondary afferents conducting GVA of CN IX lie and where they project.

Answer 4

Secondary sensory neurons of GVA lie in the caudal solitary nucleus. Project (assuming bilaterally) to the reticular formation and hypothalamus to control respiration, cardiac output, and blood pressure.

Question 5

Describe where the cell bodies of primary afferents conducting GSA of CN IX lie and where they peripherally and centrally project.

Answer 5

Primary sensory neurons of GSA lie in the inferior (petrosal) and superior (jugular) glossopharyngeal ganglia.
Peripherally they project to the external ear, inner tympanic membrane, upper pharynx, and posterior 1/3 of the tongue.
Centrally they project to the descending nucleus of V via the descending tract of V.

Question 6

Describe where the cell bodies of secondary afferents conducting GSA of CN IX lie and where they project to.

Answer 6

Secondary sensory neurons of GSA lie in the descending nucleus of V and project to the (assuming contralaterally) thalamus via the ventral trigeminothalamic tract. Thalamic relay is VPM.

Question 7

Describe where the cell bodies of primary afferents conducting SVA of CN IX lie and where they peripherally and centrally project.

Answer 7

Primary sensory neurons associated with SVA lie in the inferior (petrosal) glossopharyngeal ganglia.
Peripherally they project to the posterior 1/3 of the tongue to conduct taste.
Centrally they project to the rostral portion of the solitary nucleus via the solitary tract.

Question 8

Describe where the cell bodies of secondary afferents conducting SVA of CN IX lie and where they project.

Answer 8

Secondary sensory neurons associated with SVA lie in the rostral solitary nucleus and project to the thalamus (assuming contralaterally).

Question 9

Describe the pathway of SVE of CN IX

Answer 9

Cell bodies of corticobulbar fibers lie in the cerebral cortex and project bilaterally to the nucleus ambiguous of the medulla to synapse on LMNs which innervate the stylopharyngeus muscle.

Question 10

Describe the pathway of GVE-P of CN IX

Answer 10

Pre-gang cell bodies lie in the inferior salivatory nucleus and project axons which travel with IX and the tympanic and lesser petrosal branches of IX to synapse at the otic ganglion. Post-gang cell bodies project along the auriculotemporal nerve to the parotid gland.

Note: pre-gang cell bodies are modulated by input from the hypothalamus and olfactory system

Question 11

Describe where the cell bodies of primary afferents conducting GVA of CN X lie and where they peripherally and centrally project.

Answer 11

Primary sensory neurons associated with GVA lie in the inferior (nodose) ganglion.
Peripherally they project to the aorta, larynx, pharynx, trachea, lungs, esophagus, stomach, and intestines.
Centrally they project to the caudal solitary nucleus via the solitary tract.

Question 12

Describe where the cell bodies of secondary afferents conducting GVA of CN X lie and where they project.

Answer 12

Secondary sensory neurons associated with GVA lie in the caudal solitary nucleus. They project bilaterally to the reticular formation and hypothalamus to provide reflexive control of cardiac, respiratory, and gastrointestinal systems. Also project to the dorsal motor nucleus of X to act on GVE-P of X.

Question 13

Describe where the cell bodies of primary afferents conducting GSA of CN X lie and where they peripherally and centrally project.

Answer 13

Primary sensory neurons associated with GSA lie in the superior (jugular) and inferior (nodose) ganglia.
Peripherally they project to the larynx, pharynx, skin of the ear, external acoustic canal, external tympanic membrane, and dura of the posterior cranial fossa.
Centrally they project to the descending nucleus of V via the descending tract of V.

Question 14

Describe where the cell bodies of secondary afferents conducting GSA of CN X lie and where they project.

Answer 14

Secondary sensory neurons associated with GSA lie in the descending nucleus of V and project contralaterally to the VPM of the thalamus via the ventral trigeminothalamic tract.

Question 15

Describe the pathway of SVE of CN X

Answer 15

Corticobuilbar fibers project bilaterally to the nucleus ambiguous of the medulla. Here LMNs join CN X to innervate the pharyngeal constrictor muscles, soft palate muscles, and intrinsic laryngeal muscles.

Note: innervation of these muscle groups is bilateral except for that of the palatoglossus muscle, which is contralateral.

Question 16

Describe the pathway of GVE-P of CN X

Answer 16

Pre-gang cell bodies lie in the dorsal motor nucleus of X. Their axons traverse the descending tract of V to exit the medulla with the rest of the fibers which make up CNX to synapse at various post-gang cell bodies.

Note: Pre-gang cell bodies are modulated by input from the hypothalamus and caudal solitary nucleus.

Question 17

Describe where the cell bodies of primary afferents conducting SVA of CN X lie and where they peripherally and centrally project.

Answer 17

Primary sensory neurons associated with SVA lie in the inferior (nodose) ganglion.
Peripherally they project to the epiglottic valleculae.
Centrally they project to the rostral solitary nucleus via the solitary tract.

Question 18

Describe where the cell bodies of secondary afferents conducting SVA of CN X lie and where they project.

Answer 18

Secondary sensory neurons associated with SVA lie in the rostral solitary nucleus and project to the thalamus (assuming contralaterally).

Question 19

Describe the pathway of GSE fibers associated with CN XI

Answer 19

UMNs project contralaterally through the lateral corticospinal tract to LMNs which lie in the ventral horn from the pyramidal decussation to the level of C5. Axons of LMNs exit the spinal cord as rootlets between the dorsal and ventral roots and ascend to enter the cranial vault through foramen magnum. These axons will then exit the cranial vault through the jugular foramen to innervate the SCM and trapezius muscles.

Question 20

Describe the pathway of GSE fibers associated with CN XII

Answer 20

Corticobulbar fibers descend from the primary motor cortex in the genu and posterior limb of the internal capsule to contralaterally innervate LMNs in the hypoglossal nucleus of the medulla. Hypoglossal nucleus also receives input from the solitary and trigeminal nuclei about taste and touch to allow for the reflexes of swallowing, chewing, and sucking.