9/2 Vestibular System - Crockett Flashcards
vestibular system functions
- senses…
- which way is up
- direction of movement
- maintain posture using vestibulospinal and cervical spinal reflexes
* allows head and trunk to move together or indep - control reflexive eye movements (cerebellar and oculomotor pathways)
- vestibulo-ocular reflexes keep eyes still when head moves
- vestibulo spinal reflexes enable skeletomotor system to compensate for head movements
- detects 2 forms of acceleration
- angular/rotational
- linear
functions in conjunction with
- vision
- somatosensation
*need at least 2 of the 3 systems to figure out what’s going on
dynamic and static nature of vestibular system fx
other systems worked with
dynamic (sensing movement through space) and static fx (sending head position)
dynamic fx:
- detecting head movement
- detecting angular acceleration (semicircular canals)
- detecting linear accelerations (otolithic organs)
static fx:
- sense position of head (primarily otolithic organs)
symptoms of vestibular disease
- vertigo
- nausea, vomiting, pallor, perspiration
- difficulty walking
- sensation of spinning or rhythmic movements
- nystagmus
- sensation of leaning/being pulled to ground
- oscillopsia
location of vestibular system
- bony labyrinth
- membranous labyrinth (within bony labyrinth, surrounded by perilymph fluid)
- sensory epithelia: receptor sheaths (containing endolymph fluid)
perilymph & endolymph
perilymph surrounds membranous labyrinth
- low in K
endolymph fills membranous labyrinth
- high in K
- difference in potential is imp for hair cell fx*
- volumes of perilymph and endolymph* are strictly controlled → overproduction leads to vestibular and auditory sx
labyrinthine infarction
inner ear infarct
- usually occurs with thrombotic narrowing of AICA or basilar artery (at AICA) opening
- usually associated with infact of brainstem and cerebellum within AICA territory
- may present with primary vestibular dysfx and/or primary auditory dysfx
semicircular canal fx
function in PAIRS
L and R horizontal canals (both angled approx 30 degrees upward)
anterior canal & posterior canal (located in same plane)
where are hair cells?
how do hair cells pick up the info they need to?
specialized regions of vestibular labyrinth contain recpetors called hair cells
- ampullae of semicircular canals contain ampullary crest (thickened epithelium populated by hair cells)
- ampullary crest is covered by cupula (gelatinous mass)
- cupulas have mass → inertia gives it some lag which ensure that hair cells perceive that lag and sense what’s going on
- better for angular accel than for linear accel
types of hair cells
- nerves associated
- location
- function
2 kinds of hair cells:
1. type I hair cells
- have a primary sensory afferent (aka nerve calyx) surrounding the root
- both afferent and efferent communication with hair cell through primary sensory afferent
- also has efferent nerve terminal with indirect conection (to nerve calyx → hair cell) which can modulate hair cell fx
- location: tend to be at peak of crest (prob primary type of cell that detects movement of cupula)
2. type II hair cells
- have a primary sensory afferent making a single connection
- have an efferent nerve terminal making a direct connection too
- location: tend to be at periphery/base of crest
hair cell stereocilia show directional polarity with 40-70 stereocilia arranged in size with long kinocilium at one end
- kinocilium fx: bent one way or another → opening of Fe channels
arrangement of vestibular hair cells and relation to fx
afferent nerve is constantly active
- bending of hair cell stereocilia TOWARDS kinocilium → increased rate of firing in afferent (depolarization)
- bending of hair cell stereocilia AWAY FROM kinocilium → decreased rate of firing in afferent (hypoerpolarization)
explain nystagmus
medial vestibular nudles on both sides has neurons that carry signals to cause eye movements that compensate for head movement
- head rotates left → incr firing on left side → eye rolls right to compensate (and vice versa)
- brain is constantly comparing signals from these two nuclei to determine which way to move the eyes
IF RIGHT SIDE IS INJURED,
- L firing > R firing → brain reacts as if head moving to L → eyes roll right (slow component), then snap back to left (fast component)
- aka leftward nystagmus
response to linear accel
utricle contains macula : thickened epithelium oriented in the horiz plane containing hair cells
- covered with gelatinous material embedded w crystals of CaCO3
- head tilt results in bending of sterocilia
- best response to linear acceleration in horiz plane
saccule contains macula : thickened epithelium oriented in vertical plane
- same setup
- best response to linear accel in vertical plane
directional sensitivity in utricle, saccule
within utricle, hair cells are polarized towards the striola (indentation)
implication : any given head tilt activates some hair cells but not others!
within saccule, hair cells are polarized away from striola
benign paroxysmal positional vertigo
caused by otoconia detaching from otolithic membrane of utricle and getting stuck in a semicircular canal
subtypes: (generally uni but sometimes bilateral)
- depend on which semicirc canal involved
- 80-90% post. canal
- free-floating (canalithiasis)
- attached to cupula (cupulolithiasis)
vestibular nuclei
several nuclei in the brainstem are associated with the vestibular system
- medial vestibular nucleus
- vestibulo-ocular reflex
- vestibulo-cervical reflex
- lateral vestibular nucleus
- control of posture
- vestibulo spinal reflex
- superior vestibular nucleus
- vestibulo-ocular reflex
- vestibulo-cervical reflex
- descending (inf) vestibular nucleus
- integration of inputs from vestibular labyrinth and cerebellum
diff fx reflecting diff afferent inputs
