Cranial Nerves*

Question 1

What does CN I do?

Answer 1

The Olfactory Nerve:
- Smell
- Clinical Test: Hold strong smelling substance under each nostril

Question 2

What does CN II do?

Answer 2

The Optic Nerve:
- Vision
- Originates in the retina of the eye
- Clinical Tests: Snellen Chart, Test Visual fields (4 quadrants).

Question 3

What does CN III, CN IV and CNVI do?

Answer 3

The Oculomotor, Trochlear, and Abducens are all three motor nerves to the extraocular muscles of the eye.

Clinical Tests: Ask patients to follow the end of the pen as they move across visual fields. Shine the torch into the eye and check for pupillary light reflex (oculomotor nerve).

Question 4

What does CN V do?

Answer 4

The trigeminal nerve is a sensory nerve to the skin of the face and underlying structures.

Three major divisions:
Ophthalmic (sensory)
Maxillary (sensory)
Mandibular (sensory and motor muscles of mastication)

Clinical Test: Sharp blunt test. Can they tell the difference between sharp and blunt?

For motor function: Ask the patient to clench teeth and protrude jaw.

Question 5

Explain the mandibular branch V3 of the trigeminal nerve (CN V). ***

Answer 5

Provides sensory innervation to the:
- Skin of the lower lip and chin.
- Lower teeth.
- Anterior 2/3 of tongue
- Floor of mouth

Question 6

Explain the ophthalmic v1 and maxillary V2 branches of CN V. *

Answer 6

V1 - Sensory innervation to the eye and upper part of the nasal cavity

V2 - Sensory innervation to the skin from the lower eyelid and upper lip.

Question 7

What does CN VIII do?

Answer 7

The facial nerve supplies motor innervation to the muscles of facial expression. It also supplies a special taste sensation to the anterior of the tongue.

The facial nerve divides into 5 divisions in the parotid gland.

Clinical Test: Ask the patient to make exaggerated facial expressions.