Vestibular Function Flashcards
Describe both vestibular and auditory hair cell structure
The apical membrane of vestibular hair cells contains one tall kinocilium and several shorter stereocilia arranged from shortest to tallest.
Auditory hair cells lack a kinocilium
Basolateral membrane synapses with one or more afferent fibers that project through CN VIII
What happens when cilia are bent towards the tallest cillium?
Additional mechanically gated cation channels are opened, further depolarizing the cell
Describe the hair cell at rest.
Some mechanically gate cation channels are open, making the cell somewhat depolarized
What happens when cilia are bent away from the tallest cillium?
Mechanically gated cation channels are closed, hyperpolarizing the cell
Describe the ion composition of the endolymph (fluid bathing the apical surface of the hair cell) and perilymph (fluid bathing the basolateral membrane).
Endolymph: High in K, Low in Na
Perilymph: Low in K, High in Na
What type of current occurs when the mechanically-gated cation channels are opened due to cilia bending?
Inward current carried by K and Ca
What occurs when the basolateral membrane is depolarized?
Opening of voltage-gated calcium channels, triggering influx of calcium and subsequent exocytosis of synaptic vesicles containing glutamate
How is the rate of afferent fiber firing determined?
By the amount of glutamate released by the hair cells.
There is a tonic level of firing in the unstimulated state, and this firing increases or decreases in response to the degree of bending of the cilia in the hair cells
What organs are sensitive to linear acceleration?
Urticle and Saccule
What organs are sensitive to rotational acceleration?
Semicircular canals
What are otoliths or otoconia?
Calcium carbonate crystals located on the endolymph that generate shearing forces during linear movements of the head
What is the macula?
Sensory epithelium within the utricle and saccule
Composed of vestibular hair cells and surrounding support cells
What is the striola?
A dividing line on tha maculae where hair cell polarity (orientation of the cilia) abruptly changes
What is the significance of the transition of hair cell polarity and the curved surface of the maculae?
Ensures that all possible directions of linear acceleration are represented
What direction is the utricle more sensitive to?
Horizontal plane
Front-back, Left-Right
What direction is the saccula most sensitive to?
Vertical plane
Up-down, Front-Back
What are the ampulla, crista, and cupula of the semicircular canals?
Ampulla: Swelling of the base of the semicircular canal
Crista: Sensory epithelium within the ampulla
Cupula: Gelatinous mass over the crista where hair cell cilia extend into
What occurs during the rotation of the head in paired canals?
The cupulas are deformed in opposite directions in paired canals, producing opposite changes in hair cell membrane potential
The hair cells in the canal towards which the head is rotating are depolarized
What are the pairs of semicircular canals?
Left horizontal vs right horizontal
Left anterior vs. right posterior
Right anterior vs. left posterior
What is vestibular adaptation?
Semicircular canals respond to angular acceleration and therefore, their output adapts during constant velocity rotation
