Vestibular System (Dennis) Flashcards
Peripheral receptor apparatus
Inner ear
Head motion/position
Central vestibular nuclei
In brainstem, takes and distributes info that controls motor and spatial stuff
Vestibuloocular network
Aka vestibular nuclei, involved in control of eye movements
Vestibulospinal network
Coordinates head movements, axial musculature and postural reflexes
Vestibulothalamocortical network
Conscious perception of movement/spatial orientation
Rotational head movements detected by
Translational head movements detected by
Semicircular canals
Otolith organs on the utricle and saccule hair cells
Perilymph and endolymph
Perilymph lines the bony labyrinth while endolymph lines the membranous labyrinth
Endolymph dysfunction leads to vestibular disease
What supplies the vestibular system?
Labyrinthine artery off the AICA
Also stylomastoid artery
Occlusion will compromise vestibular functions
Meniere’s disease
Cause:
Clinical:
Increase in normal endolymph volume, resulting in distention of membranous labyrinth (hydrops)
Clinical: fluctuating hearing loss, vertigo, nystagmus, nausea, can’t stand etc.
How do you treat Meniere’s?
Diuretic and self-restricted diet or implant a shunt to drain the endolymph
Type 1 and Type 2 hair cells
Has lots of stereocilia and 1 kinocilium
Innervated by CN VIII
Stereocilia moving away and towards kinocilium de- or hyperpolarizes the cell
Ampullae:
What happens here?
Hair cells cristae at the base of the ampulla and extend into the cupula
Rotational accelerations > displace endolymph > cupula bends to some side > displace the sterocilia
Maculae:
What happens here?
Hair cells on the otolith membrane covered with otoconia on utricle and saccule
Linear acceleration > displace the otoconia > bend stereocilia
Innervation to the vestibular system
Primary afferents from CN VIII from the ampullae and maculae project to the vestibular nuclei
Vestibular nuclei:
Directionally selective. Record direction, speed of movement and head position
Has vestibulovestibular fibers and spinovestibular fibers
Vestibulovestibular fibers vs. spinovestibular fibers
- reciprocal connections with analogous contralateral nucleus
- arise from all SC levels to provide proprioceptive input
Vestibulocerebellar fibers pathway
From the vestibular nuclei course through the juxtarestiform body in the inferior cerebellar peduncle and to the cerebellum
Primary vs secondary vestibulocerebellar fibers
Primary - target dentate nucleus, terminate as mossy fibers
Secondary - target the flocculonodular lobe, fastigial and dentate nuclei
Cerebellovestibular fibers
Target vestibular nuclei
Control eye movements, head movements and posture
Dizziness vs vertigo
Dizziness - spatial disorientation
Vertigo - spinning or turning, illusion of body motion
Subjective vs Objective vertigo
Subjective: patient thinks they’re spinning
Objective: environment is spinning
Benign paroxysmal positional vertigo
Otoconail crystals separate from the otolith and get lodged in the cupula (cupulolithiasis) leading to cupula deflections
Brief episodes of vertigo when changing body position
Vestibular Schwannoma
Benign tumor in the cerebellopontine angle that originates in schwann cells of vestibular root. Tumor impinges the structures entering the internal acoustic meatus (CN VII, VIII and labyrinthine artery)
Hearing loss, gait difficulties and tinnitus
Vestibular neuritis
Possibly caused by edema of the vestibular nerve. Patients usually have recent hx of URI
Severe vertigo, n, v, no hearing loss
Lateral vestibulospinal tract
Arise from lateral and inferior vestibular nuclei > project to ipsilateral spinal cord
Extensor control for posture maintenance
Topography of the lateral vestibulospinal tract
Anterorostral - cervical axons
Posterocaudal - lumbosacral axons
Medial vestibulospinal tract
Arise from the medial vestibular nucleus > MLF > cervical SC
Stabilize neck and extensor muscles
Vestibulocolic reflex
Medial vestibulospinal tract stabilizes head via activation of neck musculature
How do vestibular info reach the thalamus?
All vestibular nuclei project to the VPM of the thalamus
Target the primary somatosensory cortex, parietoinsular vestibular cortex and posterior parietal cortex
Lesions in the parietoinsular and posterior parietal cortices
- vertigo, unsteadiness
- confusion in spatial awareness
Vestibuloocular reflex
Head rotations > activate semicircular canals > vestibular input about head motion > counter rotation of eyes > stabilize your eye while head is moving
Slow phase vs fast phase movement
- counter rotation (eye directed to direction opposite of head rotation)
- reset the eye rapidly (reach limit of the eye turning that far, reset to central position)
Nystagmus
Exaggerated slow and fast phase eye movements. Repetitive uncontrolled movements. Basically cannot fixate
Spontaneous nystagmus
Unilateral damage to vestibular system. No input from the side of the damaged vestibular system
Causes spontaneous nystagmus, vertigo
Peripheral damage to vestibular system:
Usually labyrinth damage or CN VIII damage. Causes imbalance of input between left and right systems
Central damage to vestibular system
Localized to brainstem or cerebellum. Will also affect other pathways, not just vestibular system
Impaired voluntary saccades and smooth pursuit.
What is the caloric test?
Test vestibular labyrinth function without moving head.
Use water to alter the endolymph > alters CNVIII firing rate.
Warm water = mimic turning head to irrigated side while cold induces opposite effect
COWS
Cold Opposite side Warm Same side
Oculocephalic reflex
Rotate head, patient’s eyes should stay focused centrally. If not, then you get doll’s eyes. Indicates brainstem dysfunction
Only works for comatose/unconscious patients, since conscious patients can voluntarily control their eye movement
