vestibular system Flashcards
old dogs can suffer a ____ problem with their vestibular system
temporary
vestibular disease sudden onset of symptoms
twisting and rolling on the ground as if terminally confused; eyes move rapidly back and forth (nystagmus)
the vestibular system
- monitors the position and movement of the head
- gives us our sense of balance and equilibrium
- helps coordinate movements of the head and eyes
- coordinates adjustments to body posture
what happens when the vestibular system is disrupted
- unpleasant, stomach turning feelings we associate with motion sickness (vertigo and vomiting)
- disequilibrium
- uncontrollable eye movements
vestibular labyrinth
within bony labyrinth of inner ear
otolith organs
utricle, saccule
- detect linear acceleration of head
- head tilt
- gravity is a linear acceleration
- otoliths detect tilt of head relative to gravity
3 semicircular canals
- sensitive to head rotation
- angular acceleration of head
these sensory functions are carried out by ____ cells, which communicate with axons of the vestibular portion of the 8th nerve, whose cell bodies lie in ____ ____
hair; scarpa’s ganglion
all bodies moving in three dimensions have six degrees of freedom:
3 translational and 3 rotational
otoliths: utricle and saccule
axes
- detect linear accelerations along the 3 translational axes: x, y, x
- static head tilts relative to direction of the force of gravity
kinocilium
tallest stereocilia
movement of the ____ toward the ____ opens mechanically gated channels and depolarizes it
stereocilia; kinocilium
movement away from the kinocilium ____ the cell
hyperpolarizes
vestibular hair cells are located in the ____ and the ____ and in 3 juglike swellings called ____ in the base of the semicircular canals
utricle; saccule; amupllae
arrows indicate direction of ____ deflection
depolarizing
utricle and saccule detect ____ ____ and ____ ____ of the head induced by tilting or translational movements of the head
static displacements; linear accelerations
what is the macula
the sensory epithelium consisting of hair cells and supporting cells
hair bundles are within a ____ ____ which is covered by ____
gelatinous layer; otoconia
what do otoconia do to the otolithic membrane
make it heavier than fluids around it
when head tilts gravity causes ____ ____ to shift relative to sensory epitheloum
otolithic membrane
what does shearing cause
displacement of hair cell bundles and a receptor potential in hair cell
during linear accelerations of the head there is also a “shearing” motion betwen the ____ ____ and the ____ ____
sensory epithelium; otolithic membrane
the greater mass of the ____ ____ causes it to temporarily lag behind the ____ ____, leading to transient displacement of hair cell bundle
otolithic membrane; sensory epithelium
hair cell response is
linear acceleration
transient
during static tilt hair cell response is
sustained
constant acceleration due to gravity
what type of response is of the vestibular nerve axon from an otolith organ to forward and backward changes in head tilt
sustained response
what type of response is of the vestibular nerve axon from an otolith organ to forward and backward acceleration of the head
transient response
hair cells on opposite sides of the ____ have opposing directional polarities
striola
what organs are responsive to head displacements on all directions
otolithic
utricle is mainly concerned with motion in the ____ plane
horizontal
saccule mainly concerned with motion in the ____ plane
vertical
at the base of each semicircular canal is a bulbous expansion called the
ampulla
within the ampulla is the sensory epitheloum called the ____ that contains the hair cells
crista
the hair bundles of the ampulla extend into a gelatinous mass called the
cupula
how is the cupula distorted by movements of the endolymphatic fluid
when the head turns in the plane of one of the semicircular canals, the inertia of the endolymph produces a force across the cupula, moving it away from the direction of head movement and causing displacement of the hair bulbs
when cupula moves in the appropriate direction, all the hair cells are
depolarized
when the cupula moves in the opposite direction all the hair cells are
hyperpolarized
head rotation moves the cupula in opposite directions for the two partners, resulting in:
opposite changes in their firing rates
what is angular acceleration
transient response of vestibular nerve axon from left and right horizontal semicirculat canals to left rotation of the head
hair cells in the left horizontal canal ____ when the head turns left
depolarize
hair cells in the right horizontal canal ____ when the head turns left
hyperpolarize
what are the 3 reflexes of central pathways for stabilizing gaze, head and posture
- maintain equilibrium and gaze during movement
- maintain posture and balance
- maintain mucle tone
lateral vestibulospinal tract
- ipsilateral forelimb and hindlimb extensors
- balance
medial vestibulospinal tract
bilateral to motor neurons for neck
vestibulo-ocular reflex (VOR)
head rotation activates semicircular canals in inner ear and drives compensatory eye movements to stabilize image of visual world on the retina
optokinetic nystagmus
induced by looking at moving visual stimuli, such as moving horizontal or vertical lines, and/or sripes
postrotatory nystagmus
if one spins in a chair continuously and stops suddently, the fast phase of nystagmus is in the opposite direction of rotation, known as the “post-rotatory nystagmus”, while slow phase in in the direction of rotation
pathologic nystagmus
damage to one or more components of the vestibular system - labyrinthitis or vestibulitis or vestibular disease
