Cranial nerve

Question 1

What are CN1 -12 and their fx

Answer 1

CN I - olfactory
CN II - optic 
CN III - oculomotor
CN IV - trochlear
CN V - trigeminal 
CN VI - abducens
CN VII - facial
CN VIII - vestibulocochlear
CN IX - glossopharyngeal
CN X - vagus
CN XI - accessory
CN XII - hypoglossal

Question 2

Motor or sensory or both

Answer 2

Mnemonics: Some Say Money Matters But My Brother Say Big B Matter More

Question 3

CN I test

Answer 3

ask pt if their sense of smell change recently

• ddx of CNI nerve defect is upper respiratory infection

Question 4

CN II test

Answer 4

VA
Visual field
direct opthalmoscopy

Question 5

CN 3, 4 test

Answer 5

1. look for ptosis and anisocoria (unequal size of pupil)
   if ptosis and mydriasis (dilated pupil) present = CN III palsy
   if ptosis and mitosis (constricted pupil) = Horner’s syndrome
2. pupillary light reflex - swinging flash light test (direct and consensual pupilloconstriction) = CN3
3. accommodation reflex - ask pt to focus on a distant object then focus on your fingertip ~5 cm directly in front of nose (look for convergence and bilateral pupil constriction)
   = CN4 (superior oblique)

Question 6

Horner’s syndrome triad

Answer 6

1. miosis
2. ptosis and apparent enophthalmos (sunken eyes)
3. anhidrosis (ipsilateral loss of sweating

due to interruption of sympathetic supply to face.

Ex. at brainstem (vascular disease, demyelination)

at cord (syringomyelia)

at thoracic outlet (Pancoast’s tumour)

at somewhere along sympathetic trip on internal carotid artery into the skull and orbit

Question 7

CN 5

Answer 7

sensory test: on the side of face with cotton ball then microfibre. 3 branches- ophthalamic, maxillary, mandibular

motor test: clench jaw palpation. move jaw from side to side.

Question 8

Weber’s test

Answer 8

tuning fork (256 or 512 Hz) on the centre of forehead.

Normal - sound is heard at centre of forehead

nerve deafness - sound is louder on the normal side

conduction deafness - sound is louder on the abnormal side

Question 9

Rinne’s test

Answer 9

tuning fork (256 or 512 Hz) on mastoid process until they can’t hear it then move to be in line with external meatus

normal - sound is audible again at EM

nerve deafness - same as normal (air and bone conduction are reduced equally) = Rinne’s positive

conduction deafness - no note is audible at EM = Rinne’s negative

Question 10

Lower vs upper motor neuron lesion in CN12

Answer 10

tongue, face, palate has bilat UMN innervation
so a unilateral lesion in UMN often causes no deviation

if there is deviation, unilateral lesion in LMN