Vestibular System Flashcards
What are the five divisions of the vestibular system?
Peripheral receptor apparatus Central vestibular nuclei Vestibuloocular network Vestibulospinal network Vestibulothalamocortical network
What is the peripheral receptor apparatus?
Inner ear, responsible for relaying positional changes of head
What are the central vestibular nuclei?
Brain stem, receives input from peripheral receptors and distributes it to control motor activities and spatial orientation
What is the vestibuloocular network?
Vestibular nuclei, involved in control of eye movements in conjunction with head movement
What is the vestibulospinal network?
Moderates head movement with axial musculature
What is the vestibulothalamocortical network?
Relays vestibular information to areas that can use it for movement integration and awareness of body position in space
What do the vestibular receptor organs include?
Semicircular canals and otolith organs of utricle and saccule
What types of movements do the semicircular canals relay?
Horizontal, anterior, posterior, and rotational head movements (angular acceleration)
What types of movements do the utricle and saccule relay?
Translational head movements (linear accelerations)
What innervates receptor cells in the vestibular organs?
Primary afferents of the vestibular ganglion
What is another name for the vestibular ganglion?
Scarpa ganglion
What is vestibular disease?
Disturbances in volume or ionic concentration of endolymph
Where is endolymph produced?
Endolymphatic sac
What is the blood supply to the vestibular system?
Labyrinthine a and some from stylomastoid a
What can happen from damage to labyrinthine a?
Vertigo, nystagmus, unstable gait
What is Meniere’s disease?
Endolymphatic hydrops (abnormal distention of membranous labyrinth) due to increase of normal endolymph volume. Receptors over-exposed = nausea, nystagmus, vertigo
What do hair cells do?
Register positional changes of head (angular or linear) as a result of endolymph movement
What types of hair cells are there?
Type I and II (anatomical differences). Stereocilia are staggered in height next to kinocilium
How are hair cells depolarized or hyperpolarized?
Movement toward kinocilium depolarizes cells, movement away from kinocilium hyperpolarizes cells
What is the ampulla?
Found in the semicircular canals. Hair cells embedded in cristae that extend across base of ampulla. The hair cells extend into the cupula which is moved by endolymph as head moves
What is the macula?
Found in the utricle and saccule. Stereocilia extend into otolith membrane (gelatinous) which is covered by otoconia (stones). Otoconia displaced by movement which bend underlying hair cells
How does information from the hair cells travel to the brain?
Signals from hair cells travel via primary afferents with cell bodies in vestibular ganglia that coalesce and become CN VIII. CN VIII enters at ponto-medullary junction. Targets vestibular nuclei (superior, medial, lateral, inferior) where cell bodies of second order neurons are located
What are vestibulovestibular fibers?
Reciprocal connections with contralateral nucleus to activate or inhibit vestibular organs depending on which way head is turning (R and L communication)
What are spinovestibular fibers?
Provide proprioceptive input (associated head position with postural information)
How does the vestibular system communicate with the cerebellum?
Via projection fibers (direct). Primary vs secondary vestibulocerebellar fibers
What do the primary vestibulocerebellar fibers do?
Target dentate nucleus and terminate as mossy fibers
What do the secondary vestibulocerebellar fibers do?
Target flocculonodular lobe as well as fastigial and dentate nuclei
What is dizziness?
Nonspecific term that refers to spatial disorientation
What is vertigo?
Illusion of body motion when no real motion is taking place (subjective vs objective)
What is BPPV?
Benign paroxysmal positional vertigo, common vestibular disorder. Results from changes in body position. Can be caused by cupulolithiasis
What is vestibular schwannoma?
Benign tumor originating from schwann cells of vestibular root, impinges on structures in internal acoustic meatus (CN VII, CN VIII, labyrinthine a). Hearing loss or gait difficulties
What is vestibular neuritis?
Vertigo and n/v due to swelling of vestibular n caused by virus
What is the lateral vestibulospinal tract?
Second order neurons from vestibulonuclei target SC to assist with postural maintenance. Cervical/lumbosacral cord to activate extensors
What is the medial vestibulospinal tract?
Stabilize neck flexor and extensor muscles, plays role in vestibulocolic reflex (stabilizes head w/ movements)
Where do all vestibular nuclei project?
To ventral posterior nuclear complex in thalamus (stopover point)
Where do third order neurons project?
Primary somatosensory cortex, parietoinsular vestibular cortex (PIVC), posterior parietal cortex
What is the vestibuloocular reflex?
Stabilizes retinal images during head movements. Vestibular input about head motion drives counter rotation of eyes
What is spontaneous nystagmus?
Unilateral damage to vestibular system, may cause vertigo, n/v, or falling
How do you differentiate between peripheral damage vs central damage of vestibular system?
Peripheral damage to vestibular n or vestibular apparatus - no other eye movement deficits
Central damage - problems with other eye movements (voluntary saccades and/or smooth pursuits)
What is a caloric test?
Tests vestibular function (by default vestibulo-optic reflex) without moving head. Use cold/warm water in ear and look for nystagmus (VOR). Warm water stimulates movement of endolymph, cold water inhibits.
What is the mneumonic for caloric test?
COWS: cold water - nystagmus to opposite side. Warm water - nystagmus to same side
What is the oculocephalic reflex?
Compensatory eye movements when head is rotated back and forth. “Doll’s eyes”. Seen in comatose patients with intact brainstems
