Cranial Nerves

Question 1

Give an overview of the course of the Facial nerve (CN VII) in the region of the face. Include the groups of muscles that are innovated by this nerve, as well as their actions. May use a fully labelled diagram (10)

Answer 1

N. VII leaves the skull through the stylomastoid foramen. Travels through the parotid salivary gland. Branches (above) arise from the edges of the gland and supply the groups of muscles of facial expression.
The clinically relevant groups of muscles:
 Orbicularis oculi – blinking, screwing up of eyelids
 Orbicularis oris – sphincter of mouth/lips
 Platysma – tensing skin of neck
 Occipitofrontalis – moving scalp
 Buccinator - blowing
 Small groups for moving ears, flaring nostrils, wrinkling forehead, changing shape of mouth, and so forth.

Question 2

List five clinical signs of unilateral lower motor neuron Facial nerve palsy (5)

Answer 2

LMN damage = flaccid paralysis – hypotonia or atonia, hyporeflexia.

Relate to the functions listed above.

For the signs of deficit, students should know to ask the patient to smile, show the teeth, close eyes, close lips, blow, suck, whistle, tense neck skin for shaving, wrinkle forehead, raise eyebrows, and so forth. Ptosis of lower eyelid only.

Loss of nasolabial folds; drooling, dribbling, drooping of angle of mouth, lack of expression/movement in hemi-face (entire half of UMN lower quadrant only)

Question 3

Draw and label a diagram of the central visual pathway (6)

Answer 3

To include optic nerve, optic tract, chiasma, lateral geniculate nucleus, optic radiation, striate/primary visual cortex
Retina  optic neurons  optic n  fibres of nasal/medial ½ of each retina cross at chiasm and join uncrossed fibres from the temporal ½ to form the optic tract  lateral geniculate body of the thalamus  primary visual cortex of the occipital lobe via the internal capsule.

Question 4

Outline the pathway a retinal ganglion axon would take originating in the left eye, nasal hemi-retina region and the area to which this retinal ganglion cell projects to the thalamus (3)

Answer 4

L optic nerve, Optic chiasm, R Optic tract, Lateral Geniculate Nuclues (layer receiving from contralateral eye – either P or M)

Question 5

Which part of the visual pathway would have been affected by a stroke that caused loss of vision in the temporal halves of the visual field of both eyes? (1)

Answer 5

Optic chiasma

Question 6

Name the simple test that you would use to determine whether deafness in a patient is due to blockage of the sound conduction system or due to a receptor or nervous system defect. Explain how this test allows you to distinguish between them (3)

Answer 6

Rinne’s test – if tuning fork cannot be heard through air, but sound is heard when tuning fork placed on bone, problem lies with conducting system. If the tuning fork is heard when placed on mastoid process but not when held outside the EAM then it is a conduction defect. If the tuning fork is heard over neither the bone nor the EAM, then deafness is due to neurosensory loss.