vestibular system - jullet Flashcards
The membranous labyrinth contains ___________, while the bony labyrinth contains ___________.
The membranous labyrinth contains ENDOLYMPH, while the bony labyrinth contains PERILYMPH.
Where are the saccule and utricle located?
within the vestibule (large chamber of inner ear)
Which one is attahced to the semi-circular ducts - the utricle or the saccule?
Utricle
Where is endolymph made and reabsorbed?
made by the stria vascularis and resorbed in the endolymphatic duct and sac.
Where is the communication between the perilymph and the CSF?
cochlear aqueduct
What is the cochlear duct? How is this different from the cochlear aqueduct?
The cochlear duct is a membrane-lined sac that goes out to the cochlea and it contains the organ of corti and stria vascularis. The cochlear aqueduct is where the perilymph and the CSF are in communication with one another.
There is a potential difference of +80mV between the endolymph and perilymph. What creates this ionic difference?
pumps in the stria vascularis.
How is the composition of the fluid between the endolymph different than the perilymph or even CSF?
The endolymph contains almost no Na, but a ton of K. The perilymph and CSF both contains the “normal” extracellular fluid composition of high Cl and low K.
What are the sequence of events that occur when the stereocilia is deflected towards the kinocilum?
bending of the stereocilia towards the kinocilum causes the APICAL K channels to open -> K flow into the cell from the endolymph -> rapid depolarization -> opening of VG Ca2+ channels -> Influx of Ca2+ -> vesicle fusion and release of NT onto vestibular nerve of CN VIII AND opening of K channels at the BASE of the hair cell -> efflux of K into the perilymph -> repolarization.
How is the vestibular hair cell different than the cochlear hair cells at rest?
VESTIBULAR HAIR CELLS: the ion channels at the apex of the vestibular hair cells are constitutively open (bit of tension at baseline), which eventually leads to the depolarization of the cell and subsequent NT release onto the terminal of the vestibular nerve of CN VIII. COCHLEAR HAIR CELLS: ion channels at the apex of the hair cells only open in response to mechanical vibration of the basilar membrane.
Deflection of hair cells toward the kinocilum results in depolariation and transmitter release. What happens if the hair cells bend in the opposite direction?
Bending of the stereocilia away from the kinocilium pulls the Apical K channels close, resulting in decreased vesciular NT release and hyperpolarization
What are tip links?
protein filament that links K channels on the tip of one hair with a transmembrane motor protein of an adjacent hair cell. When the stereocilia bends toward the kinocilium, the K channels open
What mechanism underlies the fact that the vestibular hair cells are constitutively open under resting conditions?
The tip links are linked to transmembrane motor proteins of adjacent kinocilium. Movement of the motor proteins towards the tip of the kinocilium occurs when there is LOW intracellular Ca2+, which restores the tension on the K channel, causing it to open it again, which will in turn open Ca channels.
T/F Under constant vestibular stimulus, the hairs of the vestibular organ can adapt to it to establish a new baseline.
True.
Where are cristae found?
ampulla of semi-circular ducts
How are the hair cells orientated in the cristae?
all oriented in ONE direction - therefore deflection in one direction produces excitation of all hair cells and deflection in the other direction produces inhibition
Where are macula found?
sacculus and utricle (think: MSU - macs sack you)
What is the striola?
a dividing line that runs down the midline of the macula of the sacculus and utricle and hair cells on either side of this line are polarized in OPPOSITE directions. Every hair cell can signal bidrectionally (increase/decrease frequency of firing depending on the direction of deflection).
How are the hair cells orientated in the saccule and utricle?
hair cells on either side of the striola (dividing line) of the macula are polarized in OPPOSITE directions
What are the purpose of the otoliths in the macula of the saccule and utricle?
increases the density of the gel and allows the gelatinous mass to respond to gravity
What type of movement do the macula of the saccule and utricle detect? How does it do this?
linear acceleration or position (gravity). If the head accelerates in the plane of the organ, the crystals tend to lag behind, bending the hair cells and nerve activity, signaling linear acceleration. If the macula is positioned vertically, the otoliths are dragged down by gravity, indicating which direction is down.
What is benign position vertigo?
when the otoliths “fall off” the macula with head injury and roll around in the inner ear, sending confusing messages to the brain about the body’s position.
