Cranial Nerves

Question 1

What does the olfactory nerve do?

Answer 1

Responsible for smell

Question 2

What is the most common cause of loss of smell and other causes?

Answer 2

URT infection is the most common cause

Other causes: increasing age, smoking, skull fracture (frontal and basal), SOL in temporal/frontal lobe

Question 3

How do we examine olfactory nerve?

Answer 3

Sense of smell on each side separately
Familiar smells (eg. peppermint/vanilla) and px must identify smell
Quick and less formal bedside test involves substances e,g coffee, soap, orange peel

Question 4

What do we assess for the optic nerve?

Answer 4

Visual acuity
Visual fields by confrontation
Fundoscopy (exam of optic fundus using opthalmoscope)

Question 5

How do we assess for visual acuity?

Answer 5

Snellen chart
Px stands 4 m from chart
Determine fraction
Top number = distance between chart and px
Bottom number = lowest line accurately read

Question 6

Describe normal, best, abnormal vision fractions from the snellen chart.

Answer 6

Normal vision: 6/6 or 4/4
Better than normal: 6/<6, 4/<4
Abnormal: 6/>6, 4/>4

Question 7

Why does the patient not remove their glasses for the snellen chart exam in neuro examination?

Answer 7

We are assessing optic nerve, not abnormalities of cornea/lens/optic fundus

Question 8

Scotoma

Answer 8

Area of visual loss surrounded by a field of normal vision

Question 9

Quadrantanopia

Answer 9

Loss of 1/4 of field of vision

Question 10

Hemianopia

Answer 10

Loss of 1/2 field of vision

Question 11

Homonymous hemianopia

Answer 11

Loss of the same half of the visual field in each eye

Question 12

Monocular blindness

Answer 12

Loss of vision in one eye

Question 13

What is the optic fundus?

Answer 13

Interior surface of the eye opposite the lens and includes the retina, optic disc, fovea, macula and posterior poles

Question 14

What is the optic disc?

Answer 14

Circular area in the retina where retinal ganglion cells leave the eye to form the optic nerve

Question 15

Name the ocular nerves.

Answer 15

III - oculomotor
IV - trochlear
VI - abducens

Question 16

What are the ocular nerves responsible for?

Answer 16

Eye movement
Eyelid opening
Pupillary constriction

Question 17

What do we examine for the ocular nerves?

Answer 17

Examine the eyes
Examine eye movements, look for nystagmus, ask about diplopia
Examine pupillary light and accommodation reflex

Question 18

Describe the components of observing the eyes.

Answer 18

Pupils - size, shape, equality
Eyelids - opening, closing, ptosis (levator palpebrae superioris)
Alignment of eyes - conjugate gaze vs strabismus

Question 19

Describe how we examine eye movements, nystagmus and diplopia.

Answer 19

Moving target using finger or pen & ask patient to follow
Look for reduction of eye movement and nystagmus
Nystagmus = rapid uncontrolled eye movement (horizontal, vertical, rotatory)
Diplopia - both eyes cannot aim at the same target

Question 20

What does the light reflex depend on?

Answer 20

Afferent optic nerve (II) and efferent oculomotor nerve (III)
Pupil constricts due to stimulation of the parasympathetic fibres supplied by the Edinger Westphal nucleus of CN III

Question 21

What causes the accommodation reflex?

Answer 21

Stimulation of parasympathetic fibres of CN III = pupil constricts due to action of pupillary constrictor muscle and lens becomes more rounded due to action of the ciliary muscle

Question 22

PERLA

Answer 22

Pupils equal and reactive to light and accommodation

Question 23

What are the signs of oculomotor nerve palsy (III)?

Answer 23

Dilated pupil on affected side
Ptosis (eyelid droop) on affected side (inactivation of levator palpebrae superioris)
Compensate for ptosis by contracting muscles of forehead
Strabismus (eyes not aligned) with a downward abducted eye on the affected side = unopposed actions of the superior oblique and lateral rectus

Diplopia, very little eye movement on affected side
Loss of accommodation and light reflex on affected side

Question 24

What are the signs of trochlear nerve palsy (IV)?

Answer 24

Extortion (outward rotation) of the affected eye - unopposed action of the inferior oblique muscle
Vertical diplopia
Weakness of downward gaze when eye is directed medially
E.g. difficulty in descending stairs or reading a book

Question 25

What are the signs of abducens nerve palsy (VI)?

Answer 25

Stabismus with the affected eye directed medially (inward deviation) - unopposed action of the medial rectus muscle

Look at an object laterally on the side of the lesion - affected eye will be unable to be abducted beyond the midline of gaze

Horizontal diplopia

Question 26

What is the trigeminal nerve responsible for?

Answer 26

Corneal reflex and jaw jerk

Question 27

What are the signs of a dysfunctional trigeminal nerve?

Answer 27

Sensory problems e.g. pain/numbness in face or motor problems causing trouble with chewing and talking

Question 28

Describe the examination of the trigeminal nerve.

Answer 28

Examine sensory function (divisions = ophthalmic, maxillary, mandibular) - light touch, superficial pain, corneal reflex
- light touch and superficial pain = same as sensory exam
- corneal reflex = blinking in both eyes when cornea is touched
Examine motor function - muscles of mastication
Examine jaw jerk

Question 29

What are the nerves supplying the cornea?

Answer 29

Sensation from cornea - ophthalmic division of ipsilateral trigeminal nerve (CN V)
Efferent pathway on facial nerves (CN VII) of both sides

Question 30

What is responsible for the jaw jerk?

Answer 30

Mandibular division of the trigeminal nerve & efferent limb by the trigeminal motor root.