2 - Cranial Nerves 1

Question 1

Cranial nerves are components of which nervous system? What do they connect directly to?

How many pairs of cranial nerves are there?

How are the cranial nerves numbered?

Answer 1

PNS components

Connect directly to the brain

12 pairs

Using roman numerals:
- low numbers = most anterior (cerebrum) - high numbers = most posterior (medulla)

Question 2

OLFACTORY NERVE ( CN I )

Involved in?
Origin?
Passes through?
Destination?

Clinical test?

Answer 2

Involved in sense of smell

Origin = receptors of olfactory epithelium

Passes through = cribriform plate of ethmoid bone

Destination = olfactory bulbs

Clinical test :
Hold strong smelling substance under each nostril

Question 3

OPTIC NERVE ( CN II )

Involved in?
Origin?
Passes through?
Destination?

Clinical test?

Answer 3

Involved in vision

Origin = retina in eye

Passes through = optic canals of sphenoid bone

Destination = diencephalon via optic chiasm

Clinical test:
Snellen chart to measure visual acuity

Question 4

CN II

Images from temporal visual field hit ___ half of retina. The axons (cross/don’t cross) at the chiasm.

Images from nasal visual field hit ___ half of retina. The axons (cross/don’t cross) at the chiasm.

Answer 4

Images from temporal visual field hit the nasal half of retina. The axons cross at the chiasm.

Images from nasal visual field hit the temporal half of retina. The axons don’t cross at the chiasm.

Question 5

CN II

Damage at optic nerve causes ..?

Damage at optic chiasm causes ..?

Damage at optic tract causes ..?

Answer 5

Some blindness in same eye

bitemporal hemianopia (loss of temporal fields)

Suffer complex visual losses

Question 6

CN III , CN IV , CN V

All 3 are ___ nerves to muscles of the eye

All 3 pass through ___ ___ ___ of sphenoid bone

CN III supplies …
CN IV supplies …
CN V supplies …

Answer 6

Motor nerves

Superior orbital fissure

CN III supplies superior, medial and lateral rectus muscles. Also the inferior oblique

CN IV supplies superior oblique

CN V supplies lateral rectus

Question 7

Damage to CN III causes ..?

Answer 7

Diplopia
Lateral strabismus
Dilated pupil in affected eye

Question 8

Damage to CN IV causes ..?

Answer 8

Vertical diplopia

Torsional diplopia

Question 9

Damage to CN V causes ..?

Answer 9

Diplopia

medial strabismus

Question 10

CN III , CN IV , CN V

Clinical tests?

Answer 10

All 3 tested by asking patient to follow pen or pen torch with eyes

For CN III - shine torch into eyes and check for pupillary light reflex. If affected, eye will not respond.

(CN V may be compressed due to intercranial pressure - is an indicator for increased intercranial pressure)