Cranial Nerve Abnormalities

Question 1

What is the name and function of CN I?

Answer 1

CN I is the olfactory nerve and is responsible for the sense of smell.

Question 2

What is the name and function of CN II?

Answer 2

CN II is the optic nerve and is responsible for carrying visual impulses from the eye to the occipital cortex via the optic tracts. It is the afferent limb of the pupillary reflex arc.

Question 3

What is the name and function of CN III?

Answer 3

CN III is the oculomotor nerve and is responsible for extraocular movements controlled by all ocular muscles except the superior oblique (CN IV) and lateral rectus (CN VI) muscles. It also innervates the muscle that elevates the upper eyelid.

Question 4

What is the name and function of CN IV?

Answer 4

CN IV is the trochlear nerve and is responsible for the superior oblique muscle, allowing the eye to look down and medially.

Question 5

What is the name and function of CN V?

Answer 5

CN V is the trigeminal nerve and provides sensation to the ophthalmic, maxillary, and mandibular regions of the face. It also provides motor function to the temporalis and masseter muscles, which cause teeth clenching and side-to-side jaw movements, respectively. It comprises the sensory portion of the corneal reflex (motor portion is CN VII).

Question 6

What is the name and function of CN VI?

Answer 6

CN VI is the abducens nerve and controls the lateral rectus muscle, allowing the eye to move laterally.

Question 7

What is the name and function of CN VII?

Answer 7

CN VII is the facial nerve and is responsible for facial symmetry and expression, carrying taste sensations from the anterior 2/3 of the tongue, and the motor portion of the corneal reflex (sensory portion is CN V).

Question 8

What is the name and function of CN VIII?

Answer 8

CN VIII is the vestibulocochlear nerve and is responsible for hearing and balance.

Question 9

What is the name and function of CN IX?

Answer 9

CN IX is the glossopharyngeal nerve and is usually considered together with CN X because they travel together and have some overlapping function. They are responsible for innervating the pharynx and palate, and both are involved in the gag reflex. CN IX provides taste for the posterior 1/3 of the tongue.

Question 10

What is the name and function of CN X?

Answer 10

CN X is the vagus nerve and is usually considered together with CN IX because they travel together and have some overlapping function. They are responsible for innervating the pharynx and palate, and both are involved in the gag reflex. CN X provides sensory, motor, and autonomic functions of viscera (i.e. glands, digestion, heart rate).

Question 11

What is the name and function of CN XI?

Answer 11

CN XI is the spinal accessory nerve and innervates the sternocleidomastoid and trapezius muscles that help control head movement.

Question 12

What is the name and function of CN XII?

Answer 12

CN XII is the hypoglossal nerve and helps control the intrinsic muscles of the tongue.

Question 13

What is the mnemonic for the cranial nerves?

Answer 13

On, On, On They Travelled, And Found Voldemort Guarding Very Ancient Horcruxes = Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory, and Hypoglossal

Question 14

What are some causes of facial nerve palsy?

Answer 14

Facial nerve (CN VII) palsy can be congenital and aquired. In 50% of cases, the cause is unknown and it is called Bell’s palsy. Other causes include otitis media, infections (especially Lyme and HSV), trauma, and neoplasms. Congenital CN VII palsy can be due to trauma or Moebius syndrome.

Question 15

What is Moebius syndrome?

Answer 15

Moebius syndrome is a congenital abnormality of the nucleus of CN VI and VII which causes facial nerve palsy and impairment of ocular abduction.

Question 16

Describe the clinical symptoms of facial nerve palsy.

Answer 16

In most cases, symptoms include an abrupt paralysis of one side of the face with associated drooling, jaw pain on the affected side, decreased tearing, inability to close the eye, and taste disturbance.

Question 17

When would one consider working up an individual with facial nerve palsy? What would the workup include?

Answer 17

If symptoms last more than 6 weeks or there is concern for an underlying etiology. Workup would include Lyme serology, electrodiagnostic studies, and imaging studies.

Question 18

What is Marcus Gunn phenomenon?

Answer 18

Marcus Gunn (jaw-winking) phenomenon is characterized by simultaneous eyelid blinking during sucking jaw movements as the child contracts the pterygoid muscle.

Question 19

What causes the Marcus Gunn phenomenon?

Answer 19

The disorder is due to abnormal innervation of the trigeminal and oculomotor nerves (aberrant innervation of the ipsilateral levator muscle of the eyelid by the mandibular branch of the trigeminal nerve).

Question 20

What complication must clinicians monitor for in patients with Marcus Gunn phenomenon?

Answer 20

This is usually a benign phenomenon but there may be associated ptosis and strabismus, and patients must be monitored for ambyopia. Surgical intervention is necessary when the associated ptosis is severe or causes amblyopia.