Cranial Nerve Examination & Diseases Flashcards
What is CN I? What is it responsible for?
olfactory nerve
mediates the sense of smell
How can CN I be evaluated?
observing the patient sniffing around
(olfactory nerve)
What is CN II? What is it responsible for?
optic nerve
carries visual signals from retina to occipital lobe of the brain
What are 3 ways to evaluate CN II?
- drop a cotton ball and watch the patient follow it to the ground
- menace response - II = visual clue, VII for blink response
- pupillary light response - II = visual clue, III for pupil constriction
What 2 nerves are responsible for the menace response?
II = visual clue
VII = blink response
What 2 nerves are responsible for the pupillary light response?
II = visual clue
III = pupil constriction
(check ipsilateral and contralateral constriction to differentiate response components)
What is CN III? What is it responsible for?
oculomotor nerve
provides motor innervation to most of the extraocular muscles (dorsal, ventral, and medial rectus) and for pupil constriction
What are 2 ways to evaluate CN III?
- observe for physiologic nystagmus when turning head (also involving IV, VI, and VIII)
- observe pupillary constriction in PLR
(oculomotor nerve)
What is CN IV? What is it responsible for? How can it be evaluated?
trochlear nerve
provides motor function to the dorsal oblique extraocular muscle and rolls globe medially
observe for dorsolateral rotation of the pupil
What is CN V? What is it responsible for?
trigeminal - maxillary, mandibular, and ophthalmic branches
provides motor innervation to muscles of mastication (masseter, temporal) and sensory innervation to eyelids, cornea, tongue, nasal mucosa, and mouth
What are 6 ways of evaluating CN V?
- palpate masseter and temporal muscles for symmetry, atrophy, and pain
- check jaw tone
- touch medial septum of nose and look for retraction
- touch the globe and observe for retraction
- palpebral response - blink reflex when touching medial canthus
- pinching the lip and observing for snarl response
(trigeminal nerve)
What is CN VI? What is it responsible for?
abducens nerve
provides motor function to the lateral rectus extraocular muscle and retractor bulbi
What are 3 ways of evaluating CN VI?
- touch globe and observe for retraction
- observe for medial strabismus
- observe for physiologic nystagmus when turning head
(abducens nerve)
What is CN VII? What is it responsible for?
facial nerve
provides motor innervation to muscles of facial expression (eyelids, ears, lips) and sensory innervation to medial pinna; provides taste to rostral tongue and parasympathetic innervation to lacrimal glands and some salivary glands
What are 5 ways to evaluate CN VII?
- menace response
- palpebral response
- observe for facial paralysis, deviation of the nose to one side, or droopy lips
- Schirmer tear test
- ear flick in response to stimulation of medial pinna
(facial nerve)
What is CN VIII? What is it responsible for?
vestibulocochlear nerve
sensory input for hearing and head position
What are 2 ways to evaluate CN VIII?
- hearing assessment - deaf animals may startle easily
- observe for head tilt, abnormal nystagmus, and presence of normal physiologic nystagmus
(vestibulocochlear nerve)
What is CN IX? What is it responsible for? How is it assessed?
glossopharyngeal nerve
provides motor and sensory innervation to pharynx for swallowing, innervates some salivary glands, and provides taste innervation from caudal tongue
eliciting gag reflex and observe for dysphagia
What is CN X? What is it responsible for?
vagus nerve
innervates the larynx esophagus, and pharynx and provides parasympathetic innervation to the heart and viscera
What are 3 ways to evaluate CN X?
- elicit a gag reflex
- observe for laryngeal paralysis
- assess for megaesophagus and regurgitation
(vagus nerve)
What is CN XI? What is it responsible for? How is it assessed?
accessory nerve
innervates cranial cervical muscles
rarely assessed and rarely a clinical problem
What is CN XII? What is it responsible for? How is it assessed?
hypoglossal nerve
provides motor innervation to the tongue
observe tongue movement and symmetry or for problems drinking and pretending food
Cranial nerves mnemonics:
What is idiopathic trigeminal neuritis? How do patients typically present?
syndrome seen in dogs with peracute onset of a dropped jaw and inability to close mouth, but no other sensory deficits or cranial nerve deficits are present
alert, responsive, without difficulty swallowing food placed on the back of the tongue
What are 4 major differentials for idiopathic trigeminal neuritis?
- mandibular fracture
- rabies
- neoplasia of mandibular nerve
- masticatory muscle myositis
How is idiopathic trigeminal neuritis treated? What is prognosis like?
supportive care with fluids and hand feeding of soft food
excellent - most dogs regain function within 1-2 weeks and return to normal within 3-4 weeks
What are 4 signs of idiopathic facial nerve paralysis?
- inability to blink (lack a menace and palpebral response)
- drooping of lip and ear
- drooling from one side of mouth
- dry eye
facial sensation is normal!
What are 3 major differentials for idiopathic facial paralysis?
- otitis media
- neoplasia of the facial nerve
- brainstem disease
What are 3 common treatments used for idiopathic facial nerve paralysis? What is prognosis like?
- tear supplementation
- thyroid supplementation (if hypothyroid)
- immunosuppressive doses of glucocorticoids
fair - complete recovery doesn’t commonly occur, but most patients can function well with moderate deficits and only need long term tear supplementation
