8 Cranial Nerves I-VI

Question 1

For reference:

Question 2

What is the brainstem?

Answer 2

Adjoins brain and spinal cord

Vital role in regulation of cardio respiratory functions + maintaining consiousness

Location of majority of cranial nerve nuclei

Ascending and descending fibres between brain and rest of body run through brainstem

Question 3

How might damage to the olfactory nerve (I) present?

Answer 3

Difficulties/changes in sense of smell

(If tested formally, do one nostril at a time)

Question 4

What is anosmia? What is the most common cause of anosmia?

Answer 4

Loss of sense of smell

Commonest cause: URT infection

Question 5

Apart from an URT, what other causes could there be for anosmia?

(CN I Olfactory nerve)

Answer 5

• Head injury (basilar skull fracture/shearing forces)
• Tumours at base of frontal lobes

Question 6

Explain why pituitary tumours cause bilateral visual symptoms.

Answer 6

Tumours compress optic chiasm

In optic chiasm: mixing of sensory fibres from right and left optic nerves

Question 7

If there is pathology affecting vision involving the optic nerve and the symptoms are only present in one eye, where is the pathology (eg lesion) likely to be located?

Answer 7

Optic nerve or retina

Question 8

Apart from pituitary tumours, give examples of other pathologies causing visual loss.

Answer 8

• Retinal detachment
• Optic neuritis
• Stroke

Question 9

How do we test the optic nerve clinically?

Answer 9

Visual acuity tests eg snellen chart

Visual fields (is part of vision missing)

Pupillary light responses

Use opthalmoscope to view patient’s optic disc

Question 10

What pathology is shown in the image on the right?

Answer 10

Papillodema (swollen optic disc)

Question 11

Why would a rise in intracranial pressure impair the function of the optic nerve?

Answer 11

Cranial nerves I and II are extensions of forebrain

Therefore extensions of the meninges

So raised ICP may impair function of optic nerve

Question 12

The visual pathway extends back from the retina towards where?

Answer 12

Primary visual cortex (occipital lobe)

Question 13

What does the communication between the optic tracts and the brainstem allow for in the midbrain?

Answer 13

Allows for certain visual reflexes eg pupillary reflexes to light

Question 14

What is a blown pupil after a head injury inidicative of?

Answer 14

Raised intracranial pressure

Oculomotor nerve (III) lies very close to edge of tentorium cerebelli

Parasympathetic fibres lie on edge of CNIII (see image)

Sphincter pupillae muscle= innervated by parasympathetic fibres on oculomotor nerve

Question 15

How would you test the function of the oculomotor nerve clinically?

Answer 15

Inspect eyelids and pupil size

Test eye movements and pupillary reflexes (to light)

Double vision?

Ptosis (eyelid droops) and eye ‘down and out’

Question 16

What can cause injury to the oculomotor nerve?

Answer 16

Question 17

What action does the trochlear do? How would you test the function of the trochlear nerve?

Answer 17

Trochlear nerve= motor to superior oblique

Depresses and abducts eyeball

Test eye movements

Diplopia (double vision as eyes don’t line up

Question 18

What is the sensory distribution of the trigeminal nerve supplying the skin?

Answer 18

Question 19

How is the function of the trigeminal nerve tested?

Answer 19

Check dermatomes

Test muscles of mastication and corneal reflex (blink reflex)

Question 20

What is trigeminal neuralgia and how does it present?

Answer 20

Sudden severe facial pain lasting about 2 mins (usually just one side of face)

Thought to be caused by compression of trigeminal nerve

Question 21

Opthalmic shingles can be sight threatening. Explain why.

Answer 21

Cornea and conjunctiva also innervated by opthalmic division of trigeminal nerve. Shingles can cause scarring of eye

Question 22

What is the corneal reflex?

Answer 22

Reflex to blink if something touches your eye as high sensory innervation density