5.3 - Cranial Nerves

Question 1

Describe the function of each of the cranial nerves

Answer 1

I: Olfactory - smell
II: Optic - vision
III: Oculomotor - eye movements (medial, superior, & inferior rectus, inferior oblique)
IV: Trochlear - eye movements - superior oblique (intorsion, “down & in”)
V: Trigeminal - sensation of face; muscles of mastication
VI: Abducens - eye movements (lateral rectus)
VII: Facial - muscles of facial expression; taste of anterior 1/3rd tongue; glands (lacrimal - tears; submandibular & sublingual - saliva)
VII: Vestibulocochlear - hearing; vestibular
IX: Glossopharyngeal - taste posterior tongue; muscles of pharynx; parotid gland (saliva)
X: Vagus - parasympathetic visceral innervation; muscles of palate, pharynx, & larynx
XI: Spinal Accessory - SCM, UT
XII: Hypoglossal - tongue movements

Question 2

Describe how to assess each of the cranial nerves

Answer 2

I - identify familiar smells
II - vision chart
III - visual tracking “+” pattern
IV - visual track “X” pattern
V - Sharp vs dull sensation of face; corneal reflex (sensory); Jaw movements
VI - visual tracking “+” pattern
VII - facial expressions; sweet vs sour taste
VIII - “Watch test” for hearing; balance
IX - Gag reflex; ability to swallow
X - “Ahhh”; gag reflex
XI - Shoulder shrug
XIII - stick out tongue

Question 3

Describe the “rule of 17s” for the CNs

Answer 3

Deviation AWAY from the lesion =
- CN 7 Facial (grimacing observation) & 10 Vagus (uvular deviation)

Deviation TOWARD the side of the lesion
- CN 5 Trigeminal (deviation of jaw) & 12 Hypoglossal (sticking tongue out)

Question 4

Describe the location of the origins of the cranial nerves

Answer 4

“Ce mi pons medu”

Cerebrum = I, II

Midbrain = III, IV

Pons = V, VI, VII, VIII

Medulla - IX, X, XI, XII

Question 5

A patient presents w/ CN VI loss. What is the resting position of the eye?

Answer 5

Adducted position
Medial strabismus

Question 6

Describe how the response to the corneal reflex can indicate which nerve may have a lesion

Answer 6

Stimulus to L eye –> no reaction
- Indicates a sensory problem = CN V

Stimulus to L eye –> R eye closes, L eye doesn’t
- Indicates a motor problem = CN VII

Question 7

Describe the visual impairments that can present from a lesion at each of the following locations

Optic N
Optic chiasm
Optic tract
Optic radiation

Answer 7

Optic N –> complete visual loss of that eye (monocular loss)
Optic chiasm –> bitemporal hemianopia
Optic tract –> BIL homonymous hemianopia
Optic Radiation –> BIL homonymous hemianopia (if through entire tract)

Question 8

Describe what information is carried through the optic radiations

Answer 8

Inferior tract (Meyer’s Loop) = inferior retinal field = superior visual field

Superior tract = superior retinal field = inferior visual field