PHYS/PHARM - Cranial Nerves

Question 1

how would you test CN I ?

Answer 1

olfactory
* ask if pt has noticed issue with sense of smell
* ask pt if nostrils feel blocked on either side
* test each nostril by occluding each other - pt closes eyes and waft smell towards them

Question 2

a pt complains of anosmia after a head injury - in which anatomical location is the lesion likely to be located?

Question 3

how do you test the light reflex in CN II?

Answer 3

optic
* check pt isn’t sensitive
* ask pt to fix on distant object
* shine light in one eye and watch response in eye, then shine again and watch response in other eye - CONSENSUAL reflex
* shine torch from side rather than directly in front

Question 4

which limb of the light reflex involves the optic nerve?

Answer 4

the afferent limb - sensory input
the efferent limbs are via the oculomotor nerve

Question 5

when testing the light reflex - what do you expect to see in both eyes?

Answer 5

constriction

Question 6

describe the limbs of the pupillary light reflex

Answer 6

• afferent limb - sensory input transmitted along optic nerve to ipsilateral pretectal nucleus
• efferent limbs - motor output transmitted to edinger-westphal nucleus on both sides of brain; each nucleus then gives rise to efferent fibres that travel in oculomotor nerve to ciliary muscles

Question 7

what does the direct pupillary reflex assess?

Answer 7

ipsilateral afferent limb
ipsilateral efferent limb

Question 8

what does the consensual pupillary reflex assess?

Answer 8

contralateral efferent limb

Question 9

what does the swinging light test assess?

Answer 9

relative afferent limb defects

Question 10

what is a relative afferent pupillary defect?

Answer 10

• afferent limb in one optic nerve is damaged
• both pupils constrict less when light is shone in affected eye compared to healthy eye
• pupils therefore appear to relatively dilate when torch swings from healthy to affected eye

Question 11

how do you test the visual fields of CN II?

Answer 11

• sit opposite pt
• ask pt to remove glasses and look at your eyes
• pt closes one eye, you close other
• wiggle finger in each quadrant (l-m)
• ask pt to tell you when they see it wiggling

Question 12

bitemporal hemianopias typically occur as a result of what?

Answer 12

optic chiasm compression by a tumour

Question 13

homonymous field defects occur due to pathology affecting what area?

Answer 13

visual pathways posterior to optic chiasm

Question 14

how do you test CN III, CN IV, and CN VI?

Answer 14

• hold finger/pen 30cm away from pt and ask them to focus on it
• ask pt to keep head still and follow pen with eyes
• move pen in H pattern
• ask pt to tell you if they have any diplopia or pain, and check for nystagmus (may suggest vestibular nerve pathology or stroke)

responsible for eye movements

Question 15

damage to CN III results in what?

Answer 15

• unopposed action of superior obliques and lateral rectus
• eye pulls inferolaterally - down and out
• ptosis and mydriasis

Question 16

what does damage to CN IV result in?

Answer 16

• only innervates superior oblique
• vertical diplopia when looking inferiorly - SO pulls eye down - pts tilt head forward and tuck in chin
• tosional diplopia - SO assists in intorsion- pts tilt head to opposite side to fuse two images together

Question 17

damage to CN VI results in what?

Answer 17

• innervates lateral rectus
• unopposed adduction of eye - convergent quint
• pts present with horizontal diplopia

Question 18

what are the 3 subdivisions of the CN V?

Answer 18

• opthalmic - sensory info from scalp, forehead, nose, upper eyelids
• maxillary - sensory info from lower eyelid, cheek, nares, upper lip, upper teeth and gums
• madibular - sensory info from chin, jaw, lower lip, mouth, lower teetch and gums - motor info to muscles of mastication

Question 19

how do you test sensory CN V?

Answer 19

• test light tough with cotton wool
• demonstrate on sternal area with consent and open eyes
• ask pt to close eyes and say yes when they feel it and if it feels the same on both sides
• dispose of cotton wool - not in sharps bin

Question 20

how do you assess the motor function of CN V?

Answer 20

• ask pt to clench teeth while feeling masseter and temporalis
• ask pt to open mouth and check jaw descends into midline, then do against resistance - assess lateral pterygoids
• ask about problems with noises sounding too loud - mandibular supplies tensor tympani which decreases vibrations of tympanic membrane

Question 21

how do you test CN VII?

Answer 21

ask pt to:
* raise eyebrows - frontalis
* close eyes tight - orbicular oculi
* blow out cheeks - orbicularis oris
* show their teeth -levator anguli oris and zygomaticus major
* purse lips shut - orbicularis oris and buccinator
* ask pt to repeat with some resisted
* ask about loud noises, dry eyes, dry mouth

Question 22

what does the corneal reflex involve?

Answer 22

• involuntary blinking of both eyelids in response to corneal stimulation
• afferent - V1 of trigeminal (opthalmic)
• efferent - temporal and zygomatic branches of facial nerve

Question 23

what is the normal result of Rinne’s test?

Answer 23

air > bone
Rinne’s positive

Question 24

what Rinne’s result suggests sensorineural deafness?

Answer 24

air > bone
Rinne’s positive due to air and bone conduction being reduced equally

Question 25

what Rinne’s result suggests conductive deafness?

Answer 25

bone > air
Rinne’s negative

Question 26

what is a normal result of the Weber’s test?

Answer 26

sound heard equally in both ears

Question 27

what webers result suggests sensorineural deafness?

Answer 27

sound heard louder on normal ear

Question 28

what webers result indicates conductive deafness?

Answer 28

sound is heard louder in affected ear

Question 29

what is conductive hearing loss?

Answer 29

• sound is unable to effectively transfer at any point between outer ear and middle ear
• eg. ear wac, otitis media

Question 30

what is sensorineural hearing loss?

Answer 30

• dysfunction of the cochlea and/or vestibulocochlear nerve
• increasing age, excessive noise exposure, viral infections

Question 31

how do you test CN VIII?

Answer 31

vestibulocochlear
* hearing part - Webers and Rinnes
* vestibular part - heel to toe walking

Question 32

what is the role of CN IX?

Answer 32

• motor info to styopharyngeus which elevates pharynx during swallowing and speech
• sensory info - taste to posteior third of tongue

Question 33

what is the role of CN X?

Answer 33

vagus
* motor info to muscles of mouth involved in production of speech and the efferent limb of gag reflex

Question 34

how are CN IX and CN X involved in the gag reflex?

Answer 34

CN IX - afferent limb
CN X - efferent limb

Question 35

how do you assess CN IX?

Answer 35

• ask about dry mouth - saliva production by parotid gland
• sensation and taste to posterior 1/3 tongue

Question 36

how do you test for CN X?

Answer 36

• soft palate and uvula movement - ask pt to say ahh and check soft palate on both sides moves upwards and that uvula moves up in midleine

Question 37

how do you test CN XI?

Answer 37

• inspect muscles SCM and trapezius
• test function with and without resistance
• SCM - ask pt to turn head both ways and then against resistance
• trapezius - ask pt to raise/shrug shoulders and then with resistance

Question 38

how do you test CN XII?

Answer 38

• ask pt to open mouth and inspect for wasting and fasciculations at rest
• ask pt to protrude tongue and observe for deviation - occurs towards side of hypoglossal lesion
• put fingers on cheek and ask them to push tongue against it

Question 39

what occurs with hypoglossal nerve palsy?

Answer 39

• atrophy of ipsilateral tongue
• deviation of tongue when protruded towards side of lesion - occurs due to overaction of functioning genioglossus muscle of unaffected side of tongue