Case studies: sensory and motor systems

Question 1

An unreactive dilated pupil suggests damage to which cranial nerve?

Answer 1

CN3

Question 2

Why does double vision occur in patients with CN3,4 or 6 damage?

Answer 2

When a patient looks in a certain direction - if only one eye can look in that direction you get a disparity between the images seen by each eye resulting in double vision

Question 3

Which 2 muscles are involved in elevating the eyelid - how is each innervated?

Answer 3

Levator palpabrae superioris - CN3, PS

Superior tarsal muscle - Sympathetic control

Question 4

Why would demyelination of neurons lead to loss of muscle tone when relaxed?

Answer 4

Because normal reflexes maintain tone - reflex pathways come in at the dorsal columns so are heavily myelinated thus affected by demyelination

Question 5

What is Tabes Dorsalis, what infection can it result from?

Answer 5

Progressive demyelination of the dorsal columns

Can occur in the tertiary phase of syphillis

Question 6

How is Romberg’s test carried out, how can it be interpreted?

Answer 6

Patient is asked to close eyes whilst standing up. Swaying or any loss of balance would be a positive Romberg’s test and would indicate loss of proprioception

Question 7

If a patient had loss of spinothalamic sensation in C4 dermatome, what level is the ventral white commissure likely to be damaged and why?

Answer 7

C2 - because spinothalamic sensations run into the spinal cord and then run up 2 spinal cord levels before crossing to the contralateral spinothalamic tract
Thus the fibres from the C4 dermatome cross the ventral white commisure at C2

Question 8

What is syringomelia?

Answer 8

A chronic progressive disease where the central canal forms a longitudinal cyst or cavity