731 Vestibular System

labyrinth

the system of fluid filled structures within the inner ear, encompassing both cochlear and vestibular components

endolymph

fluid within the membranous labyrinth; its movement is essential for vestibular sensory transduction

perilymph

fluid located between the bony and membranous labyrinths

cupula

gelatinous structure in the ampulla into which crista ampullaris hair bundles project; displaced by endolymph movement

otoconia

calcium carbonate crystals embedded in the otolithic membrane; add mass and inertia

hair cell

mechanoreceptor cell that converts physical deformation into an electrical signal via mechanotransduction

kinocilium

the tallest ciliary structure of the vestibular hair bundle; it’s orientation determines whether bending causes depolarization or hyperpolarization

where is the vestibular apparatus housed

within the labyrinth of the temporal bone

what do the peripheral organs of the ear do

detect moement and position

semicircular canals

three looped structure arranged in different planes perpendicular to one another enabling detection of rotation in any plane

horizontal canal

excitation with the ipsilateral horizontal rotation

posterior canal

excitation with rotation in the posterior canal plane

anterior canal

excitaton with rotation in the anterior canal plane

what is each semicircular canal filled with

endolymph

ampulla

at the end of each semicircular canal and houses the crista

what are the two otolith organs and what do they do

• utricle

• saccule

specialized organs for detecting linear acceleration and head positio

utricle

macula oriented primarily in the horizontal plane; detects horizontal linear acceleration and tilt

saccule

macula oritnted primarily in the vertical plane; detects vertical linear acceleration and tilt

vestibular nerve

a division of cranial nerve VIII that carries afferent signals from the peripheral vestibular organs to the brainstem

vestibular input

head rotation, linear movement, and position relative to gravity

visual input

motion in the external environment and orientation relative to visual references

somatosensory input

body position, movement, and contact with support surfaces from muscles, skin, joints, and pressure receptors

how to hair cells bend to send signals

beinding toward the kinocilium depolarizes the cell; bending away hyperpolarizes it

vestibular system function

• gaze stability

• postural stability/balance

• orientation in space

vestibulospinal reflex

skeletal muscle extensor activity triggered by ipsilateral vestibular stimulation

what is the purpose of the vestibulospinal reflex

to stabilize the body (maintain head in upright position) coordinating head and neck movements with the whole body

vestibulo-ocular reflex (VOR)

excitatory impulses travel to the oculomotor nuclei activating the R (ipsilateral) medial rectus and the left (contralateral) lateral rectus, while inhibiting each muscle’s antagonist