Cranial Nerves

CN I

Olfactory - sensory

• smell

• anosmia: lost sense of smell

• parosmia: distorted sense of smell

CN II

Optic - sensory

• Vision tested w/ Snellen Chart (visual acuity, visual fields/peripheral vision)

• Accomodation - eyes converge, pupils constrict, lens convexity

• direct light reflex

• indirect light reflex

Direct light reflex

CN II & III

Indirect (consensual) light reflex

CN II & III

CN III

Oculomotor - motor

• levator palpebrae, inf. oblique, superior, medial, and inferior rectus mm.

• parasympathetic: ciliary mm. (lens shape) and constrictor papillae

• direct light reflex

• indirect light reflex

• accommodation

• Strabismus

• ptosis

Strabismus

CN III

• deviation of one or both eyes, usually a fixed deviation (think: damage to nerve and muscle not working)

Ptosis

CN III

• eyelid droop d/t weakness or paralysis of levator palpebrae

Which 3 CNs are tested together and how?

CNs III, IV, VI using Cardinal Fields of Gaze (aka “H in space”) LR6SO4/3

Pnemonic - S vs M

Some Say Money Matters But My Brother Says Big Butts Matter Most

Pnemonic - CNs

Oh Oh Oh Once One Takes The Anatomy Exam Very Good Vacations Are Happening

CN IV

Trochlear - motor

• superior oblique m. (down & in) - if eye is in neutral w/ CN IV damage, eye will be up & out

• “LR6SO4, all others 3”

• Only CN to exit on the posterior side of the brain stem

Which CN is the only one to exit on the posterior side of the brain stem?

CN IV - trochlear

CN V - sensory

Trigeminal - Both

• split into 3:

  • V1 = ophthamlic

  • V2 = maxillary

  • V3 = mandibular

• to face (V1-3); touch forehead, cheekbone, and chin with cotton wisp

• corneal reflex

• jaw jerk reflex

• oculocardiac reflex

• general sensation, and positional sense to the anterior 2/3 of tongue

The three branches of CN V?

• V1 = ophthamlic

• V2 = maxillary

• V3 = mandibular

Corneal reflex components (CNs, directions)

CN V afferent, CN VII efferent

How to perform corneal reflex (CN V)

Touch cornea w/ cotton wisp, both eyes blink or tear normally

• CN V afferent, CN VII efferent

How to perform jaw jerk reflex (CN V)

The mandible is tapped w/ hammer and jaw draws upward

How to perform oculocardiac reflex (CN V)

Press on eye and HR decreases

• CN V afferent CN X efferent

CN V - motor

Trigeminal - Both

• mm. of mastication

CN VI

Abducens - motor

• lateral rectus m.

CN VII - sensory

Facial - Both

• taste anterior 2/3 of tongue (sweet, sour, salty)

CN VII - motor

Facial - Both

• mm. of facial expression

CN VIII

Vestibulocochlear - sensory

• vestibular: balance

• cochlear: hearing

Vestibular: balance

CN VIII

• Mittelemeyer, Barany Caloric test, Romberg’s

• Caloric test: COWS

  • cold - opposite

  • warm - same

• Romberg’s

  • eyes open = cerebellum test

  • eyes closed = posterior columns test

Cochlear: hearing

CN VIII

• Weber, Rinne, whisper, auditory acuity / watch

CN IX - sensory

Glossopharyngeal - Both

• Gag (pharyngeal) reflex

• Uvula reflex

• Carotid reflex

• taste to the posterior 1/3 of tongue (bitter)

How to perform Gag (pharyngeal) reflex (CN IX)

Check w/ tongue depressor

• CN IX afferent, CN X efferent

How to perform Uvula reflex (CN IX)

Uvula deviates to the OPPOSITE side of lesion - AWAY from lesion

• CN IX afferent, CN X efferent

How to perform Carotid reflex (CN IX)

Massage carotids and HR drops

• CN IX afferent, CN X efferent

CN IX - motor

Glossopharyngeal - Both

• stylopharyngeus m. - elevates pharynx and larynx; dilates pharynx to permit swallowing

• “Pt reports an inability to swallow, what CN may be involved?”

CN X - sensory

Vagus - Both

• epiglottis and laryngeal mm. of swallowing (palate, pharynx, contracting mm.)

CN X - motor

Vagus - Both

• gag reflex and carotid reflexes

• uvular reflex: palate and uvula devate to the OPP side of lesion when pt says “Ahh”

CN XI

Spinal Accessory - motor

• trapezius & SCM mm.: shoulder shrug w/ head rotation against resistance

CN XII

Hypoglossal - motor

• tongue mm.: stick out tongue

• deviation to SAME SIDE of lesion; look for atrophy and fasciculations