Cranial Nerve Tests
Olfactory Nerve - applying substances with different odors to each nostril in turn
Fractures of anterior cranial fossa or cerebral tumors of frontal lobes may produce lesions of olfactory nerves
Anosmia - loss of smell
Optic Nerve
First ask patient if any changes in eyesight have been noted
Acuity tested by using charts with lines of print of varying size
Examination of optic disc - intracranial subarachnoid space extends forward around the optic nerve to back of eyeball
Retinal artery and vein run in optic nerve
Rise in CSF pressure in subarachnoid will compress thin walls of retinal vein
Results in congestion of retinal veins, edema of retina, and bulging of optic disc (papilledema)
Visual field tests
Central scotoma - loss of central area of the field
Hemianopia - blindness in one-half of each visual field
Homonymous hemianopia - loss of same region of field in both eyes
Lesion of optic tract and optic radiations
Bitemporal hemianopia - lateral halves of fields of both eyes are lost
Most commonly caused by tumor of pituitary, pressing on optic chiasm, where visual information crosses
Oculomotor
Supplies all orbital muscles except superior oblique and lateral rectus
Also supplies levator palpebrae superioris, smooth muscles related to accommodation (sphincter pupillae and ciliary muscle)
Complete third nerve paralysis - the eye cannot be moved upward, downward, or inward
At rest, the eye looks laterally (external strabismus) - lateral rectus pulls laterally, superior oblique pulls down
Patient will have double vision (diplopia) and ptosis (drooping of eyelid, loss of levator palpebrae superioris)(
Pupil is widely dilated and unresponsive to light
Accommodation of eye is paralyzed
Trochlear
Innervates superior oblique
Fourth nerve paralysis - Patient will complain of double vision and looking straight downward
Because SO is paralyzed, the eye will move medially as the inferior rectus pulls the eye downward
Trigeminal
Sensory and motor roots
Sensory root - passes to trigeminal ganglion
Opthalmiic (V1)
Maxillary (V2)
Mandibular (V3)
Motor root - joints mandibular division
Sensory function test - cotton wisp over each area of the face supplied by divisions of trigeminal nerve
Motor function - ask patient to clench teeth
Masseter and temporalis can be palpated to determine if they are contracting
Facial Nerve
Supplies muscles of facial expression, supplies anterior 2/3 of tongue with taste fibers, and is secretomotor to lacrimal, submandibular, and
Sublingual glands
Motor function test - patient asked to show teeth by separating the lips with teeth clenched, and then close eyes
Taste on each half of tongue can be tested for different types of taste
Upper motor neuron lesion - corticobulbar fibers from both cerebral cortices also innervate muscles of upper part of face
Upper motor neuron lesion will leave corticobulbar fibers intact - paralysis to lower part of face
Lower motor neuron lesion - all muscles on affected side of face will be paralyzed
Lower eyelid will droop, angle of mouth with sag, tears will flow from lower eyelid, and saliva will dribble from corner of mouth
Patient will be unable to close eye and cannot expose teeth fully on affected side
Loss of taste over anterior 2/3 of tongue - seventh nerve damage proximal to point where it gives off chorda tympani
Vestibulocochlear
Innervates utricle and saccule, vestibular system, sensitive to changes in dynamic equilibrium
Also innervates cochlea, sensitive to sound
Disturbances of vestibular function - include dizziness (vertigo) and nystagmus (uncontrollable pendular movement of eyes)
Disturbances of cochlear function reveal themselves as deafness and ringing in ears (tinnitus)
Sensory tests - patient's ability to hear voice of tuning fork should be tested, with each ear tested separately
Glossopharyngeal nerve
Supplies stylopharnygeus muscle and sends secretomotor fibers to parotid gland
Sensory fibers innervate posterio 1/3 of tongue
Sensory test - patient's general sensation and that of taste on posterior third of tongue
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Vagus
Need to test branches to pharynx, soft palate, and larynx
Pharyngeal reflex - touch lateral wall of pharynx with spatula, should cause patient to gag
Soft palate test - ask patient to say "ah"
Normally, soft palate rises and uvula moves backward in midline
All muscles of larynx are supplied by recurrent laryngeal branch of vagus, except cricothyroid muscle (external laryngeal branch)
Hoarseness of loss of voice can occur if recurrent laryngeal is damaged
Accessory Nerve
Supplies sternocleidomastoid and trapezius muscle by its spinal part
Motor test - ask patient to rotate head to one side against resistance, causing SCM of opposite side to come into action
Also, ask patient to shrug the shoulders
Hypoglossal nerve
Supplies muscles of the tongue
Lesion - tongue will deviate towards the paralyzed side
One of genioglossus muscles, which pull tongue forward, is paralyzed on affected side
The other normal genioglossus muscle pulls unaffected side of tone forward, leaving paralyzed side stationaly
This leads tip of tongue to deviate toward paralyzed side
Long-standing paralysis - muscles on affected side are wasted, and tongue is wrinkled on that side
Localizing the lesion
Sixth and seventh nerves not functioning - suggests lesion within pons of brain
Eighth and seventh nerves not functioning - suggests a lesion in internal acoustic meatus
Excessive sensitivity to sound in one eary - lesion probably involves nerve to stapedius
Loss of taste over anterior 2/3 of tongue - seventh nerve damage proximal to point where it gives off chorda tympani
Abducens
Innervates lateral rectus
Sixth nerve paralysis - patient cannot turn eye laterally
When looking straight ahead, lateral rectus is paralyzed, so unopposed medial rectus pulls eyeball medially
Internal strabismus
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