Flashcards in Vestibular Function Deck (75):
What are the three systems that are utilized for the sense of body position in space?
What is the basis for the Romberg test?
The fact that the vestibular system alone is not adequate to maintain balance while standing
The Vestibular system has a role in what three major functions?
2. Postural tone and equilibrium
3. Stabilization of the eyes in space during head movements
What are the two otolith organs?
What are the three parts of the semicircular canal?
What are the sensory receptors in the vestibular system?
If the stereocilia are bent towards kinocilium, then what happens to the cell (depolarization or hyperpolarization)? What happens to neurotransmitter release as a result of this?
Depolarization--increases neurotransmitter release
If the stereocilia are bent away from kinocilium, then what happens to the cell (depolarization or hyperpolarization)?
hair cell hyperpolarizes and decreases neurotransmitter release.
Each otolith organ contains what structure for the hair cells?
Where is the macula within the utricle? What type of movement does it sense?
Floor of the utricle so horizontal when head is upright--Maximal response to head tilt is seen when the head starts in upright position.
How is the macula of the saccule oriented?
oriented vertical to the ground when the head is upright
Otoliths are crystals of what chemical? What is their purpose?
CaCO3--bend cilia of the hair cells
The vestibular organs are sensitive to what type of movement?
Nerves innervating the otoliths organs have what type of firing rate when head is upright? What about when moving?
Upright = steady, high frequency
Changes in response to head tilt
How are the semicircular canals arranged relative to one another?
True or false:A rotation which maximally stimulates one of the 3 canals does not stimulate the other two.
Hair cells in the ampulla/cupula are stimulated by what type of acceleration.
What are the interconnections between stereocilia?
Which are the sensing hairs and which is the big, stable hair cells (kinocilia vs stereocilia)?
Stereocilia = bending bits
Kinocilia = straight
What are the ion changes that occur with depolarization of the hair cells?
K ions flow into the cell, causing depolarization, and opening of a Ca channel
What is the relative [K] in the endolymph? Perilymph?
Endolymph = high
Perilymph = low
For depolarization of a hair cell, is K being actively or passively brought into a hair cell?
Bending sterocilia towards the kinocilia hyperpolarizes or depolarizes hair cells?
True or false: all the hair cells of the ampulla, saccule, and utricle are in the same plane
False--all in different planes
The brain compares what from the right and left ears to determine its position? How do the right and left stereocilia compare?
Firing rate of stereocilia, which should be polar opposites of each other
Anterior canal output on one side is compared to output from what part of the other ear?
posterior canal from the other ear since both are maximally affected by the same head turn
Receptors in the ampulla respond to what type of movement?
Horizontal cells are not quite horizontal. Bending the head to what angle will bring them parallel to the ground
What is the striola?
layer of otoliths
What is the stimulus/force that hair cells respond to?
The Brain uses information from both ears. Abrupt loss of vestibular function in one ear can cause severe symptoms. Why?
since patient’s brain interprets tonic activity from intact ear as response to head movement.
Vestibular function deteriorates with age. Approximately what percent of vestibular hair and nerve cells are lost by 70 years of age.
What is the firing rate like from hair cells (variable, stable, etc)?
Turning your head in the horizontal plane will stimulate the horizontal semicircular canal. Let's say you turn your head to the right. What happens to the firing rate of the right and left horizontal semicircular canal ampulla hair cell firing rate?
Increase in right sided firing
Decrease in left sided firing
What is the ocular reflex?
If head is tilted to one side, eyes rotate in the opposite direction.
the ocular reflex depends on what?
tonic input from the utricle and saccule
What is the firing pattern like for the vestibular nerve?
Will fire in response to changes in velocity, but then calm back down
Loss of the vestibulo-ocular reflex would result in what symptoms?
Loss of this reflex would make fixation difficult or impossible while the head was turning
True or false: the VOR still occurs in the dark
There are two eye movements that occur with movements of the head, the fast and the slow. Which is part of the VOR?
What is the fast eye movement seen in testing the VOR?
Flicking back to midline once the eyes get to the most lateral edge of the eye
What drives the fast eye movements seen in testing the VOR?
The fast movement is probably driven by the same brain areas that are responsible for saccadic eye movements.
The vestibular system feed into which nuclei to stimulate the VOR? Where does this nucleus send projections to?
The vestibular nuclei, which go to the abducens nucleus
When turning to the right, which vestibular nucleus is stimulated, the right or the left?
Left, causing leftward eyemovement
Review conjugate eye movement innervation
Abducens nerve sends projections to the contralateral oculomotor nuclei to simulate the medial rectus to move eye in the same way the abducens nucleus moves the lateral rectus
If a test pt is spun about at a constant velocity in a chair, what happens to the VOR?
What is rotatory nystagmus?
Slow phase of nystagmus that compensates for the turn
If turning a pt to the right, which way does the SLOW phase of nystagmus go?
If turning a pt to the right, which way does the FAST phase of nystagmus go?
Do the fast phase and slow phase of nystagmus utilize the same neural circuitry?
Pts with a coma will only exhibit what type of nystagmus (fast or slow)?
If there is a lesion in one of the semicircular canals, what will happen?
What is post rotatory nystagmus?
vestibular nystagmus that occurs AFTER a person stops turning.
What causes post rotatory nystagmus?
endolymph has inertia it continues to move after head stops turning, so even though person is now stationary, signals from semicircular canals make person feel that they are turning in OPPOSITE direction from original movement.
If patient is tested by turning to LEFT, when chair stopped patient has illusion that they are turning in which direction?
Eye movements of post rotatory nystagmus correspond to what? Thus, the slow eye drift is to what side?
the ILLUSIONARY turning
Thus the slow eye drift is opposite the illusionary side
Cold sided irrigation of an ear will produce the slow nystagmus toward or away from that ear? Fast?
Cold side will fire less, causing Slow phase toward the cold ear, fast away from the cold ear
Warm sided irrigation of an ear will produce the slow nystagmus toward or away from that ear? Fast?
Warm side will fire more, causing slow phase away from the ear, and fast phase toward the ear
If a pt is comatose, which part of nystagmus will they have: slow or fast?
The COWS mnemonic gives the direction of which phase of nystagmus: fast or slow?
Fast, thus slow will be opposite
What specific damage to the brainstem will cause the VOR to be absent?
damage to CN VIII
What is the Doll's eye maneuver?
Movement of the neck of a comatose pt should elicit VOR so they stay looking at you
Never try the Doll's maneuver until you are sure of what?
No c-spine injury
What is the cause of BPPV?
Loose otoliths causing aberrant stimulation. Thus pts will feel fine with a certain position of their head
Does BPPV cause heading loss?
What is cause (maybe) of Meniere's syndrome?
Imbalance between production and reabsorption of endolymph,
What are the symptoms of Meniere's syndrome?
Vertigo with fullness in ears and hearing loss
How can Meniere's syndrome cause permanent damage?
Damage to hair cells
Some vestibular afferents go right from the vestibular apparatus to what lobe of the cerebellum?
The cerebellum receives direct connections from the vestibular apparatus and sends them where?
To the vestibular nuclei
What are the vestibular nuclei? (how many, where in the brainstem are they, and what do they do)?
Four pairs of nuclei in the rostral medulla/caudal pons
Project fibers to the MLF
What is the tract that projects from the vestibular nuclei to the motor nuclei of the oculomotor nuclei? What is the function of this connection?
Medial longitudinal fasciculus
Allows for vestibulo-ocular reflexes
What is the function of the lateral vestibulospinal tract? Where does this tract begin?
This tract participates in control of motor neurons of limb and trunk for maintenance of balance and posture.
Begins in the vestibular nuclei, which receive signals from the vestibular apparatus
What is the function of the medial vestibular tract?
This tract helps control neck muscles and thus head position.