Vestibular System (Stephens) Flashcards
- a test that consists of moving patient’s head quickly from vertical to vertical and horizontal to horizontal
- a positive test is if the patient’s eyes remain stationary looking forward and do not move w/ the head movements
- tests the neuronal link between the vestibular nuclei and the system that controls horizontal gaze
- also tests the function of the oculomotor and abducens nerves and their central connections to the vestibular system
Doll’s eye maneuver
- a test that involves placing cold water in the ear canal of a patient and then placing warm water in the same ear canal
- tests the vestibulo-ocular reflex, by testing the function of the oculomotor and abducens nerves and their central connections to the vestibular system
- the cold water causes a convection current in the semicircular duct, which stimulates the cristae ampullaris and causes eyes to look toward the side of stimulus w/ nystagmus to the opposite side of stimulus
- normal test in conscious patient: w/ cold water would cause patient to look toward stimulus w/ side to side eye movements (nystagmus) away from stimulus; w/ warm water would cause patient to look away from stimulus w/ nystagmus toward stimulus (the mnemonic COWS can be used to remember nystagmus: cold opposite, warm same)
- a positive test in conscious patient would be the absence of these eye movements, which suggests ipsilateral vestibular impairment of the stimulated lateral semicircular duct
- normal test in unconscious patient: cold water results in horizontal gaze toward stimulus; nystagmus will be absent in comatose patient b/c it is controlled by cerebrum, and there will be deviation of eyes toward ear being tested
- positive test in comatose patient indicates midbrain damage and poor prognosis
ice water caloric test
What is the purpose of the vestibular system and what are the primary afferent sources used in vestibular system proprioception?
- purpose: signal changes in position of head w/ respect to gravity (static detection) and motion of head (kinetic detection)
- primary afferent sources: vision, general proprioception from the body, and vestibular info from membranous labyrinth
What are the possible findings of the Doll’s eye maneuver and what do these findings indicate?
- head turns right
- horizontal gaze to the left; normal finding
- right adducts, left neutral; left VI palsy
- right neutral, left abducts; right III palsy
- no reponse (neutral gaze); possible midbrain damage
- head turns left
- left neutral, right abducts; left III palsy
- left adducts, right neutral; right VI palsy
- no response (neutral gaze); possible midbrain damage
*in the unconscious patient without cervical injury, side to side movement of head results in horizontal movement of the eyes in the opposite direction*
Why is the Doll’s eye maneuver contraindicated in the a suspected C-spine injury?
The DEM is contraindicated in this situation because the test requires the physician to turn the patient’s head, and this is something that could worsen a C-spine injury thus it could harm the patient further by performing this exam
What are the ice water caloric test findings and what are they indicative of?
- Right ear being tested
- right eye abducts, left eye adducts: normal finding (horizontal gaze to the right)
- right eye abducts, left eye no response: left III nerve palsy
- right eye no response, left eye adducts: right VI nerve palsy
- no eye response: left III and right VI nerve palsies OR midbrain damage (deep coma state)
- Left ear being tested
- right eye adducts, left eye abducts: normal finding (horizontal gaze to the left)
- right eye no response, left eye abducts: right III nerve palsy
- right eye adducts, left eye no response: left VI nerve palsy
- no eye response: right III and left VI nerve palsies OR midbrain damage (deep coma state)
- neuroepithelial cells located in cristae ampullaris of semicircular ducts and maculae of utricle/sacculus
- polarization of these cells is triggered by flow of endolymph in semicircular ducts
- head movement alters direction of endolymphic current and provides info to vestibular nuclei and vestibulocerebellum regarding head position and movement
- input strongly influences direction of gaze and position of head/body
vestibular receptors
What is the course of the vestibular nerve entering the brainstem?
- vestibular nerve enters the brainstem at the pontomedullary sulcus
- courses beneath (anterior to) the inferior cerebellar peduncle (restiform body)
- axons terminate in vestibular nuclei or vestibulocerebellum
- some axons directly enter cerebellum via juxtarestiform body (medial portion of RB)
- central process of primary neuron bifurcates into ascending and descending branches and terminates to: vestibular nuclei, fastigial nuclei, or flocculo-nodular lobe
What are the four principal tracts from the vestibular nuclei and what are their general functions?
- medial longitudinal fasiculus (MLF): eyes turn to side of stimulus
- medial vestibulospinal tract (MVST): head turns to side of stimulus
- lateral vestibulospinal tract (MVST): body turns to side of stimulus
- reticular formation (RF): nausea/vertigo/visceral disturbances
What is the general function of the medial longitudinal fasiculus (MLF)?
- link between vestibular influences and horizontal gaze
- Doll’s eye maneuver and ice water caloric test are vestibulo-ocular responses, meaning they use MLF
- horizontal gaze to either side is controlled by contralateral MLF
What is the general pathway of MLF?
fibers from vestibular nuclei and adjacent paramedian pontine reticular formation (PPRF) decussate in the lower pons
↓
fibers ascend to oculomotor nucleus in midbrain (located adjacent to midline and fourth ventricle/cerebral aqueduct)
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oculomotor nucleus fibers to medial rectus are ipsilateral
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oculomotor nucleus fibers decussate to abducens nucleus and then to lateral rectus, thus they are innervated by contralateral fibers
(what the above means is that horizontal gaze to either side is controlled by contralateral MLF)
What is the general pathway of the medial vestibulospinal tract (MVST)?
originates from medial vestibular nucleus, mostly comprised of uncrossed descending fibers
↓
terminates in intermediate gray matter of cervical and upper thoracic levels of spinal cord
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influences muscles of the neck, upper back, and proximal upper limbs
(key link in coordinating head position relative to eye movements)
What is the general pathway of the lateral vestibulospinal tract (LVST)?
originates from the lateral vestibular (Deiter’s) nucleus
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descends in the lateral funiculus of the SC
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terminates in the ipsilateral intermediate gray matter of all levels of the SC
(coordinates positioning of body relative to head position/gaze, fascilitates extensor tone and reflexes of antigravity axial and appendicular muscles)
What is the connection of the reticular formation with vestibular nuclei?
- vestibular nuclei project bilaterally into RF
- affects somatic motor system (postural tone)
- provides a mechanism for visceral autonomic disturbances a/w vestibular simulation (pallor, nausea, vertigo, and vomiting)
What deficits and symptoms would be seen with a unilateral lesion of the vestibular system?
- ipsilateral signs and symptoms
- nystagmus: toward side of lesion
- vertigo: dizziness opposite the lesion
- postural impairment: assessed using Romberg test which if positive indicates sensory ataxia, if patient is ataxic w/ negative Romberg’s this is cerebellar ataxia
- patient tends to fall toward side of lesion (midline lesions of cerebellum cause truncal ataxia)
- eyes, head, and body tend to turn toward side of lesion
- visceral disturbances: nausea, vomiting, pallor
(deficits may attenuate w/ time due to visual and general proprioceptive compensation)
TLDR: vestibular symptoms including nausea, vomiting, postural impairment, and nystagmus
What signs and symptoms would be present w/ a medial longitudinal fasciculus (MLF) lesion?
- internuclear ophthalmoplegia (INO): disturbance of horizontal gaze, may have abnormal horizontal gaze in opposite direction of the lesion, convergence of accommodation also present
- INO named for the side of oculomotor impairment, thus the MLF lesion is ipsilateral to the non-adducting eye
- right INO due to right MLF lesion: horizontal gaze to the left demonstrates no adduction of right eye and nystagmus of left eye
- left INO due to left MLF lesion: horizontal gaze to the right demonstrates no adduction of left eye and nystagmus of right eye
(accommodation unaffected by INO b/c does not use MLF, instead uses corticotectal fibers)
TLDR: gaze abnormalities away from side of lesion
What signs and symptoms would a lesion of the paramedian pontine reticular formation result in?
(PPRF background: horizontal and lateral gaze center, enhancement of RF, coordinating area for oculomotor system, located adjacent to abducens nuclei, PPRF sends fibers to abducens nucleus for ipsilateral lateral rectus and to contralateral MLF for contralateral oculomotor nucleus to medial rectus)
- paresis/paralysis of horizontal gaze toward same side of the lesion
- gaze preference away from side of the lesion
(caused by destruction of fibers that course from PPRF to ipsilateral abducens nucleus and contralateral oculomotor nucleus)
TLDR: paralysis toward side of lesion, gaze preference away from lesion
