Vestibular system

what does the vestibular system do

stabilizes gaze, posture, and head orientation during movement.

what does the vestibular system do in regards to gravity

it converts the effects of gravity (linear and rotational accelerations of the head) into neural impulses

what are there three axis of head rotation

• yaw: around the z axis (vertical)

• pitch: around the y axis (ear to ear)

• roll: around the x axis (nose to the back of head)

what is the stimulus for the utricle and the saccule

linear acceleration and static head positioning in regards to gravity

what is the receptor structure of the utricle and the saccule

macula with otolithic membrane and otoconia

for the utricle and the saccule, do orientation changes occur continuously or sporadically?

continuously; around a stroll so that all directs are encoded

what is the stimulus for the semicircular canals

rotational acceleration (head turning)

what is the receptor structure of the semicircular canals

hair cells in the ampulla under a gelatinous cupula

why do the vestibular hair cells (kinocillium) and vestibular nerves fire tonically?

vestibular cells are like auditory hair cells where many are open at rest, so vestibular nerve are tonically active

How does the otoconia bend hair bundles

• Small crystals (otoconia) sit in the otholitic membrane (gelatinous) above the hair cells.

• when the head tilts, the crystals rub against the hair cells and bend them.

• The utricle then compares sustained head tilt with transient/ST forward acceleration and deceleration.

vestibular hair transduction

the same as auditory

1. Stereocilia bending toward the kinocilium opens channels; K+ enters from the endolymph and the cell

depolarizes.

2. Voltage-gated Ca2+ channels open and transmitter is released onto the afferent.

3. Bending away from the kinocilium reduces K+ entry and Ca2+, so the cell hyperpolarizes and firing drops.

4. Because many channels are open at rest, nerve firing rises and falls around a baseline.

how does the capula bend hair bundles

in each of the semicircular canals, theres an ampulla holding the crista, hair bundles, and capula. when head rotation occurs, the endolymph moves, which displaces the scapula and bends the hair bundles

how does the left and right horizontal canals work together during a head turn

During a head turn, endolymph flow bends stereocilia in one horizontal canal in the excitatory direction (afferents increase firing) and the other canal's hair cells hyperpolarize (afferents decrease firing).

what does the vestibule-ocular reflex do?

eye movements that counter head movements—maintains gaze

what are the key stations of the vestibule-ocular reflex

Medial vestibular nucleus, medial longitudinal fasciculus, abducens and oculomotor nuclei, extraocular muscles

what is the vestibule-spinal reflexes

maintains balance and posture of the body

what are the key stations of the vestibule-spinal reflex

Lateral vestibular nucleus, lateral vestibulospinal tract

what does the vestibule-cervical reflex do

processes proprioception, visual, and vestibular stimuli

what are the thalamic and cortical targets of vestibular input

the ventral posterior nucleus of the thalamus. as for cortical regions: its the cerebrum and the pons; which contain neurons that respond to propioceptive, visual, and vestibular stimuli