Test 2: lecture 18 balance Flashcards
problems with the vestibular system lead to __-
Unpleasant, stomach turning feelings we associate with motion sickness
– vertigo and vomiting
Disequilibrium
Uncontrollable eye movements
___ can detect linear acceleration of the head
utricle and saccule (otolith organs)
___detect tilt of head relative to gravity
otoliths (utricle and saccule)
linear acceleration and head tilt
___ are sensitive to head rotation and acceleration
3 semicircular canals
These sensory functions are carried out by ___which communicate with axons of the vestibular portion of the 8th nerve, whose cell bodies lie in ____
hair cells
Scarpa’s ganglion
A ll bodies moving in three dimensions have six degrees of freedom:
3 translational and 3 rotational
Otoliths utricle and saccule detect___ along the 3 translational axes, x,y, and z
linear accelerations
•Static head tilts relative to direction of the force of gravity
semicircular canals detect ___ of the head
rotational or angular accelerations
___ is the tallest stereocilia
kinocilium
in the semicircular canals the CN 8 axons make up the ___
crista ampullaris
in the otolithic organs (utricle and saccule) the Cn8 axons make up the ___
macula
stereocilia of hair cells are held together by ___
tip links
when the stereocilia move toward the kinocilium what happens?
depolarization
the endolymph has lots of K, movement toward the tallest opens the mechanically gated channels and K rushes in causing depolarization
when the stereocilia move away from the kinocilium what happens
mechanically gated K channels close → hyperpolarization
what is the fluid where the stereocilia sit?
endolymph
(has lots of K)
Movement of the stereocilia ___ the kinocilium opens mechanically gated channels and depolarizes cell. Movement ___from the kinocilium hyperpolarizes the cell
toward
away
Vestibular hair cells are located in the ___ and in three juglike swellings called ___ in the base of the semicircular canals
utricle and the saccule
ampullae
direction of depolarization in the ampulla
center line in the utricle and saccule where depolarization is in different directions
striola
____detect static displacements and linear accelerations of the head induced by tilting or translational movements of the head
Utricle and Saccule
the sensory epithelium consisting of hair cells and supporting cells
otolithic membrane
macula
what are the crystals that sit on top of the gelatinous cap in the utricle and saccule
otoliths/otoconia
the crystals and the gelatinous cap
otolithic membrane inside the utricle and the saccule
___ are calcium carbonate crystals
otoconia (otoliths)
___make otolithic membrane heavier than fluids around it
Otoconia
how does utricle or saccule work
when head tilts gravity causes otolithic membrane to shift relative to sensory epithelium.
“Shearing” causes displacement of hair cell bundles and a receptor potential in hair cell
movement toward the kinocilium → depolarization , movement away → repolarization
saccule → movement away from center line (striola) → depolarization
utricle → movement toward the center line (striola) → depolarization
why is there a “shearing” motion between the sensory epithelium and the otolithic membrane.
During linear accelerations
The greater mass of the otolithic membrane causes it to temporarily lag behind the sensory epithelium, leading to transient displacement of hair cell bundle
hair cells move in the opposite direction of the head, temporarily lag
During static tilt hair cell response is ___
sustained
constant because gravity is constant
During linear accelerations hair cell response is ___
transient
only occurs with change in velocity
head tilt backwards causes ___, head tilt forward causes ___
depolarization
hyperpolarization
___ mainly concerned with motion in the horizontal plane
Utricle
movement toward the center → depolarization
___ mainly concerned with motion in the vertical plane
saccule
movement away from the striola → depolarization
___ Detect angular acceleration that result from rotation of the head
semicircular canalas
At the base of each semicircular canal is a bulbous expansion called the ___
ampulla
In the semicircular canals, within the ampulla is the sensory epithelium called the ___ that contains the hair cells
crista
The hair bundles of the semicircular canal extend into a gelatinous mass called the ___.
cupula
___ cannot flow through the cupula
Endolymph
cupula is the gelatinous mass on the hair bundle of the crista in the ampulla of the semicircular canal
endolymph move ___ to the direction of movement of the head
opposite direction
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 a displacement of the hair bundles
When the head turns in the plane of one of the semicircular canals, the ___of the endolymph produces a force across the ___, moving it away from the direction of head movement and causing a displacement of the hair bundles
inertia
cupula
what is the direction of the hair cells in the semicircular tubules?
all in the same direction ( they all either depolarize or hyper polarize based on the direction from the kinocilia)
Head rotation moves the ___in opposite directions for the two partners, resulting in opposite changes in their firing rates
cupula
semicircular canal on the right will depolarize and left will repolarize (they are opposite of each other)
if I turn my head to the left what direction is the endolymph in the semicircular canals
the left will go right this will cause depolarization
the right will go right will cause hyperpolarization
___ response of vestibular nerve axon from left and right horizontal semicircular canals to left rotation of the head ( angular acceleration)
Transient
only respond to change not constant acceleration
Hair cells in the left horizontal semicircular canal depolarize when the head turns ___
left
Hair cells in the right horizontal semicircular canal ___ when the head turns left
hyperpolarize
pathway from vestibular area to brain
vestibular → CN8 → vestibular nuclei → up to the brain (either the lateral vestibulospinal tract → antigravity muscles or the medial vestibulospinal tract → neck)
lateral vestibulospinal tract
Ipsilateral forelimb and hindlimb extensors
(antigravity muscles)
balance
medial vestibulospinal tract
bilateral to motor neurons for neck
run through the medial longitudinal fasciculus (MLF)
MLF carries information to the neck motor neurons and the ____ nerves
3,4,6 extra ocular motor neurons → stabilize gaze (VOR- vestibulo ocular reflex)
VOR
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
head rotates L → eyes rotate R → gaze remains the same place
movement causes depolarization in semicircular canal on one side → this will stimulate the CN3 on the same side to contract the medial recti, it will also cause the CV6 nucleus to cause the lateral rectus of the opposite eye to contract and go through the MLF and also cause the medial recti of the same eye to contract
vestibular nystagmus
eyes try to stay on same place can’t keep up cause head is moving, will have a slow phase when it is trying, then a fast snap back phase
optokinetic nystagmus
moving in car → follow a tree then snap to new tree
. A nystagmus induced by looking at moving visual stimuli, such as moving horizontal or vertical lines, and/or stripes.
Optokinetic nystagmus
If one spins in a chair continuously and stops suddenly, the fast phase of nystagmus is in the opposite direction of rotation, known as the “____,” while slow phase is in the direction of rotation.
Postrotatory nystagmus
damage to one or more components of the vestibular system e.g., Garth: Labyrinthitis or vestibulitis or vestibular disease
pathologic nystagmus
Dogs with idiopathic vestibular disease have some combination of the following symptoms:
A head tilt
- They are unsteady on their feet and may fall over
- Head tilts and animal falls toward the side of the lesion
- They circle in one direction or even roll across the floor
- Their eyes flick back and forth, up and down, or rotate in a circle (this is called nystagmus)
- An unwillingness to eat due to nausea
- Vomiting
Moral of the Story: Don’t kill old rolling dogs
