PHYS/PHARM - Cranial Nerves Flashcards
how would you test CN I ?
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
a pt complains of anosmia after a head injury - in which anatomical location is the lesion likely to be located?
how do you test the light reflex in CN II?
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
which limb of the light reflex involves the optic nerve?
the afferent limb - sensory input
the efferent limbs are via the oculomotor nerve
when testing the light reflex - what do you expect to see in both eyes?
constriction
describe the limbs of the pupillary light reflex
- 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
what does the direct pupillary reflex assess?
ipsilateral afferent limb
ipsilateral efferent limb
what does the consensual pupillary reflex assess?
contralateral efferent limb
what does the swinging light test assess?
relative afferent limb defects
what is a relative afferent pupillary defect?
- 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
how do you test the visual fields of CN II?
- 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
bitemporal hemianopias typically occur as a result of what?
optic chiasm compression by a tumour
homonymous field defects occur due to pathology affecting what area?
visual pathways posterior to optic chiasm
how do you test CN III, CN IV, and CN VI?
- 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
damage to CN III results in what?
- unopposed action of superior obliques and lateral rectus
- eye pulls inferolaterally - down and out
- ptosis and mydriasis
what does damage to CN IV result in?
- 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
damage to CN VI results in what?
- innervates lateral rectus
- unopposed adduction of eye - convergent quint
- pts present with horizontal diplopia
what are the 3 subdivisions of the CN V?
- 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
how do you test sensory CN V?
- 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
how do you assess the motor function of CN V?
- 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
how do you test CN VII?
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
what does the corneal reflex involve?
- involuntary blinking of both eyelids in response to corneal stimulation
- afferent - V1 of trigeminal (opthalmic)
- efferent - temporal and zygomatic branches of facial nerve
what is the normal result of Rinne’s test?
air > bone
Rinne’s positive
what Rinne’s result suggests sensorineural deafness?
air > bone
Rinne’s positive due to air and bone conduction being reduced equally
