Cranial Nerves, Brain Stem Reflexes, and Brain Stem Disorders Flashcards
CN1 (Olfactory)-what causes impaired smell?
-mucosal swelling and inflammation during sinusitis or an URI
what can cause permanent loss of smell
- severe head trauma
- tumor near the olfactory lobe
How do you test CN3, 4, and 6?
capital H
Clinically, what does the deficit from a complete CN3 lesion look like?
paralysis of the levator palpebrae superioris muscle may cause complete ptosis…pupil of involved eye is large and unreactive to light
What is so special about CN4 (trochlear)
only CN that exits the brain stem dorsally and decussates to innervate the contra superior oblique muscle
binocular diplopia
- more common type of diplopia and resolves if the pt covers either eye
- can be caused by lesions of CN3,4,6, or their related extraocular muscles.
monocular diplopia
- rare, occurs when looking with one eye alone
- 2/2 dislocated lens or detached retina, or psych
INO (internuclear ophthalmoplegia)
-paralysis of extraocular muscles (“ophthalmoplegia”) from a lesion between the muclei (“internuclear”) involved with lateral gaze (oculomotor and abducens nuclei)
INO interrupts the ascending medial longitudinal fasciculus (MLF)
-most common causes of MLF lesions are multiple sclerosis in younger pts and ischemic infarction in older patients
pupillary light reflex
-elicited by shining light into one eye, causing its pupil to constrict (direct response) and also the other eye (consensual response)
anatomy of pupillary light reflex
-involves retinal ganglion cells projecting b/l to pretectal area (rostral to superior colliculus) which then projects to EW nucleus of CN3
relative afferent pupillary defect (RAPD)
- may occur form partial optic nerve or retinal lesion
- after swinging flashlight test pupillary dilatation occurs b/c of relatively reduced afferent input at the affected eye
near reflex
- occurs when viewing a nearby object
- consists of:
- -pupillary constriction
- -lens accommodation (“thickening”)
- -convergence of the eyes
light-near dissociation
- selective disruption of pupillary light reflex but connections for near reflex preserved
- -aka dissociation of light and near reflexes
- -pupils only constrict d/r near reflex but not to a light stimulus
causes of light-near dissociation
- dorsal midbrain (Parinaud’s) syndrome
- classically 2/2 pineal tumor compressing midbrain
- Argyll Robertson pupils in neurosyphilis
Horner’s syndrome
-occurs from a lesion disrupting oculosympathetic pathway (three neurons in series)
-Horny PAM
Ptosis=paralysis of superior tarsal muscle
Anhidrosis=dec sweat on ipsi face b/c sweat glands have sympathetic innervation
Miosis=smaller constricted pupil, dilates poorly in darkness
what can sensory deficits not confined to the trigeminal nerve territory be due to?
- lesions in the contra thalamus or parietal lobe
- psych disorders
trigeminal neuralgia and MS
-ms lesion at the trigeminal nerve entry region into the pons is often the cause of trigem neuralgia in younger pts
trigem neuralgia and older pts
-trigem nerve branch is often compressed by a tortuous or kinked blood vessel (often the superior cerebellar artery)
trigem motor
-muscles of chewing or mastication–masseter and temporalis muscles
LMN facial paralysis
- involves CN7 and causes a paralysis of the entire ipsi half of the face
- impaired taste over ant 2/3 of tongue indicates that chorda tympani branch of facial nerve is involved
- plus hyperacusis from stapedius muscle denervation
lesions at the internal auditory meatus or cerebellopontine angle
- stuff from CN7 and tinnitus
- 2/2 acoustic neuroma (involvement of adjacent CN8)
what about a lesion at or near the facial nucleus in the pons?
create ipsi weakness of lateral gaze from involvement of adjacent PPRF and CN6
Bell’s palsy
- idiopathic facial nerve paralysis
- may be due to Herpes simplex or other viruses
- hasten recovery with corticosteroids
UMN facial paralysis
milder paralysis of only LOWER PART of contra face, SPARING forehead
palatal arch test which cranial nerve
pt say “ah”=test vagal nerve function
LMN lesion of vagal nerve
- ipsi drooping or sagging of palatal arch with uvula pointing to nml side
- hoarseness from ipsi paralysis of vocal cord muscles
LMN lesions of CN12
protruded tongue deviates toward the affected/weak side
-over time affected half of tongue will atrophy and will see fasciculations and fibrillations
crossed brain stem syndromes
-consist of CN involvement on one side and an adjacent fiber tract lesions=clinical sensory or motor deficit on the opposite side of the body
R. pontine lesion
-involves R. facial nucleus and R. corticospinal tract=LMN paralysis of entire R. half of face AND UMN paralysis of the left upper and lower limbs (left hemiparesis)
L. lateral medulla lesion
-involves L. descending spinal tract of CN5 and L. STT=deficits of pain and temp over let face and right limbs and body
Weber (medial midbrain) syndrome caused by?
- may be d/t an ischemic infarction from an occluded branch of the posterior cerebral artery
- CN3 and nearby cerebral peduncle (corticospinal and corticobulbar tracts) are involved
Wallenberg (lateral medullary) syndrome caused by?
ischemic infarction from occluded vertebral artery or its PICA branch
Weber (medial midbrain) syndrome presentation
- –ipsi oculomotor nerve lesion
- –UMN weakness of the contra face and limbs
Wallenberg (lateral medullary) syndrome features that make it a crossed brainstem syndrome?
—pain (pinprick) and temp impairment on ipsi face and contra limbs and body
—plus: hoarseness, vertigo, n/v, clumsiness
plus: nystagmus (vestibular nuclei)
:ipsi limb dysmetria (inferior cerebellar peduncle)
:ipsi Horner’s (descending sympathetic tract)
:ipsi palatal and vocal cord paralysis (nucleus ambiguus)
