Cranial nerves

Question 1

List the cranial nerves and functions?

Answer 1

CN I Olfactory: sense of smell

CN II Optic: Vision

CN III Occulomotor: All the muscles moving the eye except for superior oblique and abducent also controls the muscle responsible for the eyelid.

CN IV Trochlea: Superior oblique

CN V Trigeminal: 3 branches; opthalmic, maxillary and mandibular, sensation of the face and muscles of mastication.

CN VI Abducent: Controls lateral rectus muscle which pulls the pupil laterally (aka abducts)

CN VII Facial: 5 branches involving movements in the face. Temporal, zygomatic, buccal, mandibular, cervical. Taste to the anterior 2/3 of the tounge via the chorda tympani.

CN VIII Vestibulocochlea: hearing and balance

CN IX Glossopharyneal: Taste to the posterior 1/3 of the tounge. Sensation to the oropharynx.

CN X Vagus: Parasympathetic stimulation to most of the body including the heart and GI notably, test with gag reflex. Controls the movement of the palate.

CN XI Accessory: Motor innervation to SCM and trapezius.

CN XII Hypoglossal: Muscles of the tounge.

Question 2

Describe what you will see in a patient with the following palsies:
CN III
CN IV
CN VI

Answer 2

CN III:
The eye will be looking down and out, only the lateral rectus and superior oblique will be working.
There will be a near complete ptosis and mydriasis.

CN IV:
Patients present with vertical diplopia usually worse on downwards gaze.

CN VI:
Usually occurs unilaterally one eye will not be able to look laterally and therefore will cause a binocular diplopia.

Question 3

Describe how you can tell if a facial nn palsy is a upper or lower motor neuron lesion?

Answer 3

UMN lesions are forehead sparing due to there being bilateral innervation.

Question 4

In uvula and tounge deviation describe where the lesion is most likely to be?

Answer 4

Uvula deviates away from the lesion aka if uvula is deviated towards the left indicates a right sided CN IX & X palsy.

Tounge deviates towards the lesion, aka a tounge deviated towards the left indicates a left sided CN XII palsy.

Question 5

Describe Rhine’s and Weber’s test and the clinical significance?

Answer 5

Rhine’s test:
Twang a tuning fork and place it on the mastoid process, and then immediately in front of the ear.
In a normal person it should be louder in front of the ear indicating that air conduction > bone conduction. If this is not the case the patient has a conductive hearing loss.

Weber’s Test
A tuning fork is twanged and placed in the centre of the patients head and asked which ear the sound is loudest in, it should be equal.

If the hearing deficit is conductive then it will be louder in the affected ear.

If the hearing deficit is sensorineural then it will sound louder in the patients good ear.

Without Rhine’s test you cannot tell the deficit in Weber’s test.