Cranial nerve revision

Question 1

Most common causes of anosmia

Answer 1

• Most commonly caused by nasal infection because nasal mucous becomes thicker and fewer particles make it to the nerve dendrites
• Can also be caused by trauma to cribriform plate and ethmoid bone or olfactory groove meningioma
• Can be an early sign of dementia

Question 2

The left of our visual field in both eyes comes from where?

Answer 2

The right hand side

Vice versa for the left

Question 3

What would a lesion to the right optic nerve result in?

Answer 3

Loss of vision in right eye = monocular vision loss e.g. optic neuritis in MS

Question 4

What would a lesion to the optic chiasm cause?

Answer 4

Bitemporal hemianopia (both sides of the temporal or lateral vision is lost), pituitary tumour e.g. acromegaly

Question 5

What would a lesion to the right optic tract cause?

Answer 5

Loss of the medial vision in right eye and loss of lateral vision in the left eye = contralateral homonymous hemianopia

Question 6

Actions of the oculomotor nerve

Answer 6

1. Inferior oblique
2. Medial rectus
3. Superior rectus
4. Inferior oblique
5. Levator palpabrae
6. Parasympathetic fibres to ciliary ganglion - causes pupils to constrict

Question 7

Difference between Horner’s and 3rd nerve palsy

Answer 7

In Horner’s the pupil constricts and the eye movements are normal

3rd nerve palsy causes dilated pupil with down and out eye

Question 8

Results of Weber’s test

Answer 8

Normal hearing will produce equal sound in both ears

Conductive loss will cause the sound to be heard best in the abnormal ear

Sensorineural loss will cause the sound to be heard best in the normal ear

Your next step would be to do Rinne’s test and if this shows that conductive hearing is heard louder in front of the ear than on the mastoid process this rules out conductive hearing loss

Question 9

Function of glossopharyngeal nerve

Answer 9

Supplies taste to the posterior third of the tongue and movement of the palate

Question 10

Nerve responsible for gag reflex

Answer 10

Vagus

Question 11

Muscle wasting and fasciculation on the left of the tongue, which side is the lesion?

Answer 11

Left

• If you see wasting or fasciculation of one side of the tongue it is that side that has the cranial nerve lesion
• The tongue deviates towards the lesion