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77 Cards in this Set

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Main function of the Vestibular System (VS)
Maintain head and eye movements
What does vs sense
Angular and linear acceleration, along with the static forces of gravity and + compensatory movements to keep the body balanced
What is vestibulo –spinal reflex (VSR)
Keeps the body steady and prevent it from falling due to the forces of the gravity, they do postural adjustments and generate smooth body movements
What is vestibulo- ocular reflex (VOR)
Retinal image stability, keep the retina fixed in the image as the head is moving
What is the rate that the afferent fiber fire and what nerve is referred to as the afferent
They fire at 100spikes/sec and any change in this fire rate is due to the stereocillia on the hair cells being bent, CN8
What is the signal to the CNS when both right and left afferent are firing at the same rate
Head is not moving and therefore no compensatory head or retinal movements are launched
What happens if the right CN8 is firing at 50 spikes/ sec and left is firing at the 150
There is movement of the head and the brain + compensatory body and retinal movements, the eyes always move to the ↓ AP side, i.e. they turn toward the Right side, this is the slow movement of the eye but it can’t stay there it snaps back and that is sccade.
What are the manifestations of injury to CN8
Vertigo and nystagmus
What is vertigo
Its loss of balance due to loss of Cn8, this is illusion of motion, it feels like the whole room is spinning around you, this is NOT dizziness
What is nystagmus
It is oscillatory (jerky) eye movements, it is a reflex consisting of bilateral slow eye movements opposite to a head movement with a non compensatory fast saccadic movement to reset the eye position
Lesion on the left side, what happens to the right side
They slow eye movements is towards the left but it can’t stay there so it is snapped back and this is the fast non-compensatory movement, it is called a saccade and brings the eye back to the right. The nystagmus is named after the direction of the fast movements because it is usually seen, in this case it will be right horizontal movement, THIS IS CONSIDERED PATHOLOGICAL IF IT IS SUSTAINED OR SPONTANEOUS
What happens to the eyes if you turn the head right 2 degrees
They turn left by 2 degrees
CN in telencephalon
1 & 2
CN in midbrain
CN in Medulla
Where is 11
What is a hair cell
It is the functional unit, it is similar to the hair cell in the cochlea, every hair cell is innervated by a single afferent vestibular ganglion cell, it releases + NT like GLU or ASP on the afferent fiber TONICALLY so they have a TONIC resting discharge rate, the activity of these hair cells is under the control of efferent nerve fibers from the brain, it is usually divided in to 2 polar arrangements 1)KINOCELIUM (large ) and STEREOCILLIA (short)
What does this morphological polarity determine
It determines the body’s response to acceleration
What happens if hair cells bend towards the Kinocelia
↑ # of tip link channels open and depolarization happens, ↑ influx of K and Ca at the Apical membrane from outside of the cell to the inside, this cause ↑ release of NT at the basolateral membrane and this causes the ↑ in afferent nerve firing
What is the AP inn hair cells called
Nothing, there is no AP, hair cells never launch an AP
What happens if the stereocillia bend away from the Kinocelia
↓ # of open tip links (i.e. transduction channels), ↓ Ca and K currents, hyperpolarization, ↓ NT release and ↓ afferent nerve firing
What happens if both the stereocillia and Kinocelia are bent perpendicular
No effect
What’re the 2 solutions that bathe the hair cells
Perilymph and endolymph
What is the Perilymph? It’s make up? function?
Similar to CSF, ↓ K and ↑Na, surrounds the membranous labyrinth (which is made up of neuroepthelial cells ) and it contained by the bony labyrinth
What is the Endolymph? It’s make up? function?
It is an ECF which = ICF, ↑k, ↓ Na, contained with in the membranous labyrinth, and does not communicate with any other fluid space
How are Perilymph and endolymph separated
Via tight junctions , it these TJ are gone there would be no separation
Where is the Endolymph secreted from
By the stria vascularis in the scala media
What happen if there’s ↑ production of Endolymph
Meinere’s syndrome→ ↑ fluid pressure with in the membranous labyrinth
Where are the cell bodies for the CN8
Scarpa’s ganglia
Where are the hair cells located
The apical segment of the hair cells are embedded in the endolymph with in the membranous labyrinth, once + they release GLU on to the CN8 afferents whose cell bodies lie in the Scarpa’s ganglia, and they then synapse on the Vestibular nucleus and this then controls the eyes and balance
When the hair cell bends in one direction or the other, does it move with an electrical gradient or the concentration gradient
It move via an electrical gradient
What are the 2 peripheral end organs of vestibular labyrinth system
Maculae and Crista Ampullaries
What are otolith organs
They are referred to stones, they are located in macula (which is the membranous labyrinth), the hair cells in the macula are located underneath the Caco3 stones, there are total of 4 maculae, 2/ear, these CaCo3 crystals mechanically move the hair cells,
What is the function of the maculae
They control linear forces caused by static displacement of hair cells due to gravity and transient displacement due to the linear acceleration or deceleration, linear movement is in three planes 1)x-axis = forward backward, this is rocket sled, flex and extent the head 2)y axis does left right, this is trolly car 3) z axis does up and down, elevator, hypo or hypergravity
What are the optimal stimuli for the otolith organs
It is linear displacement, steady tilt of the head like static signals and it is not effected by the angular acceleration
What are the 2 location where maculae can be found
They are located utricle and Saccule
How is directionality conferred by the hair cells
Based on the hair cell orientation and macule position
What is the striola and how does it effect the orientation of the hair cells
It is a median that divides the hair cells and the hair cells are points towards the striola or they are pointed away form the striola, this orientation ensures that regardless of the movement of the head one side is going to be + and the other side is going to be (-), another thing to note is that the Kinocelia ( which is the tallest hair cell is always the farthest away from the striola)
Macula in Saccule controls
It controls all of the movements along the z-axis, it controls upwards and downwards like riding the elevator, detects changes in the vertical plane
What does the maculae in the utricle control
They controls movements along the X and the Y axis and it detects changes in the horizontal plane, riding a car or a head tilt
What are semicircular canals
They are 6 areas of neuroepithelium in the membranous labyrinth, 3 ampullae/ ear they control the 12 extra ocular muscles
What is the function of the semicircular canals i.e. ampullae
They detect angular acceleration as small as 0.1m/s.s, they do horizontal, vertical, and lateral
Is constant angular velocity a good stimulus for the ampullae
No, mainly became the fluid and the ampullae will eventually start to rotate at the same rate
How is angular movement transduced
The canals lie 90 degrees to each other with in the plane
What type of movement does the each axis control
X-axis→ controls roll, y axis→ controls pitch and the Z axis controls YAW. Remember z is like bar thru the nose and you roll around it, y is bar through the ears, and the Z is like bar through and this = YAW
If we were to tilt the head forward 30° which way are the ampullae oriented
They are oriented in the horizontal position, also if we were to tilt the head 60° backward or tilt the head of a supine patient 30° lateral canals will be vertical
As the head moves clockwise, the endolymph will move
Counter clockwise, it is also left behind in the membranous labyrinth and has a lag.
How does the movement of hair cells control the movement of the head
It is done via utriculopedial movement which pushes the hair cell towards the larges and this causes the depolarization, when we move the hair cells in the opposite direction it is called utriculofugal movements and this is hyperpolarization
How does the sensation of acceleration transduced
The flow of endolymph will distort the cupula as this cupula is distorted, AP are launched, and only cells in the ampullae which is at the right angle to the axis of the rotation will respond to the acceleration or deceleration, that’s when it is maximally stimulated when it is located at the right angles
How are all the cilia oriented in a given ampullary crest? What is the proper direction to launch a depolarization
They are all oriented in the same direction, in the horizontal ampulla, cilia are oriented toward the utricle, but in the other 2 they are oriented away from the utricle. Depolarization is launched when the cilia is bent towards the Kinocelia, and it is the same idea because of the orientation each hair cell is oriented in a way that depending on the stimulus one type of hair cell is going to be stimulated but the other is going to be inhibited
What happens when is moved to the left, i.e. YAW to the left
We + afferent firing form the left side and inhibit the firing from the right side and that happens because they are in the same plane also the endolymph will move towards the right, and this has no effect on the paired anterior and posterior, because they are no in the plane that the orientation is taking place
How are the canals paired
Right and left horizontal are paired, the left posterior is paired with the right anterior, and the left anterior is paired with the right posterior
What is the purpose of the VOR
It allows the eyes to move at a velocity equal to the head movement but in opposite direction of the head and this keeps the image focused on the fovea.
What is the sensitivity of the vestibular system to the constant movements
↓, this was tested and shown that the after 30 seconds of the rotation with subject’s eyes closed or in the dark, the eye movements will stop after 30 seconds and this happens because the endolymph lags behind
Where is the stimulus felt to perform the VOR
It is felt in the maculae and utricles along with the amoullae i.e. where the neuroepthelial cells are located
What is the duration from onset of stimulus and onset of the eye movements
12 milliseconds
What is the velocity of the eye movements
What is the target pursuit velocity
100 °/sec, accurately 30°/sec
What the at happens when the head moves to the right or put warm water in the right
The endolymph lags but eventually begins to move left because it heats up, the Kinocelia on the right is + while one on the left is (X), both eyes run to the left with the same velocity as the movement of the head, it keeps the visual images steady on the fovea
How is a nystagmus describes
It is described based on the movement of the fast saccadic eye which brings the eyes back to their original position
What is the pneumonic that describes the way eyes would go if we were to add cold water or hot water
COWS cold opposite and warm same
What kind of movement do we have with the cold water on a normal patient vs. unconscious
In the normal patient the fast away from the water and slow towards but in the unconscious only slow movements towards the water and this is because there are no fast movements
What do we see with warm water
The fast is towards the side where the water is being poured but the slow is away from the side the water is being poured and in an unconscious patient we only have slow movements. Remember I order for these responses to occur the patient can’t focus on anything, they have to be unconscious
What happen in a unilateral lesion in the vestibular pathway
Nystagmus will be ↓ or absent on the side of the lesion
How long does the caloric nystagmus last
It lasts as long as there is a temperature gradient
What is rotational testing
It is called Barany chair, the patient is situated in a swivel chair and rotated for 30 sec at a rate of! rev every 2-3 sec, for about 45 seconds, the nystagmus which is in the direction of the fast movement is in the direction of the chair movement, the nystagmus lasts only 30 sec because the endolymph will eventually catch up and at this point the head, the semicircular canals and the endolymph are all moving in the same direction
How can we induce a horizontal nystagmus
By putting the head upright because this makes the semicircular canals horizontal or torsional if the person is looking up at the ceiling
When do we see the optokinetic nystagmus and what effect does it have
Optokinetic nystagmus is seen when the lights are on it is seen because the eyes has something to focus on
How do we see a postrotatroy nystagmus
It is seen when the chair is brought to a full stop, this is in the direction opposite to the direction of the chair movement, this happens because when we stop the chair from moving, everything stops but the endolymph take a while to stop and it is still turning in the direction that the chair was turning, this causes ↓ firing in AP on the side chair was turning and thus slow movements on the side the chair was turning and tendency to fall all occur at the side the chair was turning
What CN does sensor to the eye? motor?
Sensory= CN2, motor= 3,6
What are some of the disorders of VS system
Benign positional vertigo, labyrinthine disease, acute peripheral vestibulopathy, ototoxic drugs
What is benign positional vertigo
Most common VS disorder, usually presents as Otoconia where the CaCo3 stone usually gets dislodged from the utricle and gets stuck in the cupula of the posterior canal and this results in brief episodes of vertigo
What is labyrinthine disease
Seasick, space sick, there are subjective syndromes that can present as vertigo, nausea, and oscillopsia (oscillations of objects that are moved) these are symptoms that the patient experiences but there are objective symptoms that the MD must be able to see to treat like nystagmus, falling or postural deviation, sweating, pallor, vomiting, and hypotension
What is acute peripheral vestibulopathy
Spontaneous attack of vertigo, it includes acute labyrinthine and vestibular neuronitis, this is characterized ↑ vomiting, nausea, vertigo, lasts about 2 weeks and we can see some degree of vestibular dysfunction can be seen
How do the ototoxic drugs show their effect
They do so by causing ↓ VOR and the main implicated drug is gentamicin
What is meinere’s disease
↑ endolymph production or it’s outflow is inhibited