vestibular system Flashcards
parts of vestibular labyrinth DIAGRAM: bony and membranous
bony labyrinth- filled with perilymph: cochlea and semi-circular canals (bony part)
membranous labyrinth- has endolymph, has utricle, saccule (2 sacs- utricle larger and closer to canals) and semicircular ducts (within canals): WITHIN bony labyrinth
functions of vestibular system
perception of motion in space reflex balance reactions to prevent gait stabilises eyes on target during head movement (vestibulo-ocular reflex) supports control of BP during rapid up/down movements causes motion sickness
components of vestibular system
semi-circular canals- angular motion of head otolith organs filled with endolymph- sense LINEAR accleration of head due to gravity
saccule forms cochlear duct, utricle forms semi-circular canals
vestibular hair cells and transduction
mechanoreceptors- has stereocilia (varying height) and a long single kinocilum- displacement towards kinocilium= depolarisation, displacement away= hyperpolarisation
semi-circular canals and function DIAGRAM
bone structures forming bony labyrith- - 3 in each labyrinth, with hair cells inside a sheet called crista (within ampulla) and endolymph- the stereocilia are covered in a cap called CAPULA kinocilia are unidirectional- acceleration phase of head rotation moves endolymph in one direction, which displaces cilia signal proportional to speed of acceleration- signals to brain that head is acclerating ANGULARLY
how semi-circular canals work DIAGRAM
constant rotation= endolymph keeps moving on both sides= on signal deceleration= canal on opposite side activated (eg going from right to left stimulates left canal)- other canal inhibited, so that brain detects rotation: canals on both side have their own tonus (firing rate)- at rest they balance out
otolith organs DIAGRAM
saccule and utricle have macula (vestibular hair cells), and above is otolithic organ,then crystals of CaCO3 (OTOCONIA)
saccule and utricle
orientation in vertical vs horizontal plane ie head tilting (NOT rotating)
how otolith organs work DIAGRAM
during HEAD TILTS and LINEAR ACCELERATION, gravity shifts membrane, which displaces hair cells through a SHEARNG motion
vestibular nuclei somatotopic organisation
primary afferent neurones of vestibular nerve go to the 4 vestibular nuclei in brain there is a somatotopic organisation- otolith sends to lateral and inferior nuclei, canals send to medial and superior nuclei
projections from vestibular nuclei- spinal cord
spinal cord (helps with upright posture and balance)- lateral vestibulo-spinal tracts sends impulse to limb muscles, medial vestib. tract sends to neck and back muscles thalamus and cortex- thalamic nuclei project to cortex nuclei of extra-ocular muscles cerebellum
vestibulo-ocular reflex DIAGRAM
function- produces eye movement in opposite direction to head movement, keeps images on target canal goes to superior/medial vestibular neurons- go to extraocular muscles- medial goes to contralateral abducens nucleus to ABDUCT eye by innervating lateral rectus muscle (left head movement= right OUTWARD eye movement), abducens nucleus projects to contralateral oculomotor nucleus to ADDUCT other eye by innervating medial rectus muscle (left head movement= left inward movement)
vertigo vs oscillopsia
sensation of spinning, either gentle or violent- you think YOU are moving
oscillopsia- you think world is moving
vestibular nystagmus
unilateral loss of vestibular function- tonus of intact canal causes eyes to go to LESIONED side due to the VOR (ie brain acting as if head turning to intact side)- normally tonuses from each side balance out this detected by brainstem which resets eye positioning with fast SACCADES= nystagmus- here you are NOT turning, your body thinks you are
oscillopsia
bilateral loss of vestibular function- everything lags behind during head movements- head shake test shows eye taken off target by head rotation, with many saccades to refocus on target: you think WORLD is moving- loss of VOR occurs
