BS545 - Vestibular

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What are the names of the chambers within the vestibular apparatus?: Saccule and Utricle.
What is the location of hair cells in the Utricle and Saccule? What gelatinous material is associated with these? What stimulus is transduced?: The macula.

Otolithic membrane.

Linear acceleration including gravity.
Which macula measures linear acceleration in the vertical plane? Includes gravity. Which macula measure linear acceleration in the horizontal plane?: Macula sacculi - lies nearly vertically on the wall of the saccule.

Macula utriculi - lies nearly horizontally on the floor of the utricle.
What are the names of the hair cells within the macula? Which is the biggest? How many (special) big ones?: Stereocillia.
Kinocillium (largest, one of these).
What movement is required to generate Action Potentials within the vestibular apparatus? Name what is moved and what direction results in increased APs.: Kinocillium and stereocilla are moved - they pivot at their base rather than bending. For increased APs, they move toward the utricle.
What is the name of the membrane in which the hair cells of the utricle and saccule are embedded?: Otolithic membrane.
What are otoliths? What is their function?: Calcium carbonate crystals within the otolithic membrane. They make the membrane denser than endolymph so the membrane "flops" around and stays "flopped" when the position of the head changes.
What is the arrangement of the hair cells in a given macula, i.e. the direction in which they face?: They are arranged with their kinocila facing in multiple directions so any tilt stimulates some cells more than others. These patterns are maintained in the branches of the eighth nerve.
What is the name of the dilation at one end of each semicircular duct?: ampulla.
What structure is contained within each ampulla? What is its composition?: A crista - transversely oriented ridge of tissue covered by suppoting cells and sensory hair cells.
How are the kinocilla aligned within the cupula?: The kinocilla are closest to the utricle.
What direction will the cupula move for increasing Action Potentials? What happens if it moves away from this structure?: Movement toward the utricle will increase the number of APs. Movement of the cupula away from the utricle will decrease the number of APs.
Name the five destinations of the vestibular output. For what purpose is vestibular information used at each of these CNS sites?: 1) -> Cerebral cortex via thalamus: conscious awareness.
2) -> CN III, IV, VI via MLF: keep eyes on target while head is moving.
3) -> Vestibulospinal tract: reflex control of ipsilateral postural muscles.
4) -> RF: Vomiting
5) -> Flocculonodular lobe: inputs for feedback control of movement.
Describe what happens in the vestibulocular reflex. No circuitry in this question.: As the head circles, the eyes will move in the opposite direction to keep the gaze fixed on a given object. When the object goes out of view, the cortex will cause the eyes to rapidly move toward center and acquire a new target.
Suppose the head is rotating counter-clockwise. Describe what is physically and electrically happening for the VOR.: 1) Initially fluid in the horizontal semicircular duct will move clockwise.
2) Cupula on left side of body will flow clockwise and will be bent toward the utriculi.
3) AP activity increased on left side.
4) Increased tone to muscles that will move the eyes to the right.
5) On the right side, the cupula will move away from the utricula, APs will decrease, tone to muscles will decrease that would move the eyes to the left. Net effect eyes move to the right as head moves to the "left".
What is the afferent limb for the VOR? What is the motor limb for the VOR?: CN VIII

CN III, IV, VI connected by the MLF.
What part of the brain drives the fast phase of nystagmus?: RF
If a leison is on the right side, what three signs will be observable?: 1) Nystagmus with left-beat
2) Lean toward the right
3) Head tilt toward the right
What is the purpose of the vestibulocollic reflex?: Keeping the head level as it rotates.
What motor limb is associated with the vestibulocollic reflex?: Fibers of the Medial Vestibulospinal Tract which projects along the MLF (medial longitudinal fasciculus).
What is the purpose of the vestibulospinal reflex?: Facilitates postural stability.
What motor limb is associated with the vestibulospinal reflex?: LVST (lateral vestibulospinal tract)
What is the significance of the tonic activity of the vestibular nucleus?: Like having foot always depressed on the gas pedal. Activity can easily be increased or decreased.
What are the small bones in the middle ear? Generic name and individual names. Give how they are interconnected to each other.: Osscles: malleus -> incus -> stapes
What muscle is attached to the malleus?: tensor tympani
What muscle is attached to the stapes?: stapedius
How is the intensity of sound sensed?: Rate of firing APs and number of nerve fibers firing.
What secondary effect can be measured as the result of OHCs firing? What is a use of this property?: A backwards wave can be formed which will move the tympanic membrane and can be heard with a special instrument.

This is a way to check the hearing pathway in a baby.
Sketch out the circuit for the VOR.: See the picture

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