Physiology of auditory & vestibular Flashcards
(33 cards)
What is the structure of the basilar membrane?
Narrow and stiff near oval/round windows
Wider and more flexible near helicotrema
Where do high vs low frequency sounds cause deflection of the basilar membrane?
High frequency - where membrane is narrow and stiff (base)
Low frequency - where membrane is loose and flexible (apex)
How is the frequency of sound (pitch) coded?
Depends on where along the basilar membrane there is the greatest deflection
What is amplitude?
Sound pressure/intensity measured in decibels (dB)
What is frequency?
Number of oscillations of air pressure per second (Hz)
How are the outer hair cells activated?
They are displaced when the pressure differential results in a shearing force against the tectorial membrane
How are the inner hair cells activated?
By fluid movement in the cochlear duct
What type of receptor is the TRPA1 channel?
A mechanotransduction ion channel
What is the advantage to a mechanotransduction channel?
They respond to stimuli much faster than a chemical signal transduction process. They are also more sensitive to stimuli
Where is endolymph found and what makes it up?
Fills the scala media and bathes the apical end of the hair cells. Similar to ICF, high in K+ and low in Na+
Where is perilymph found and what makes it up?
Foundin scala vestibuli and scala tympani, bathes the basal end of cochlear hair cells. Similar to ECF, high Na+ and low K+
How are hair cells depolarized?
Cation channels at the apical ends open when the tip links connecting hair cells are stretched. Influx of K+ (from endolymph) depolarizes the cell
How does depolarization of hair cells cause sound waves to be converted to action potentials?
After K+ depolarizes the hair cell, Ca2+ channels at the base of the hair cell open. This causes NT-filled vesicles to release glutamate onto the afferent cochlear nerve fibers
How are hair cells situated in the cochlea?
The stereocilia at the tips are embedded in the tectorial membrane and the bodies rest on the basilar membrane
What does an upward displacement of the basilar membrane do?
Causes shearing force to laterally displace stereocilia which depolarizes the hair cell
What do inner hair cells do vs outer hair cells?
Inner hair cells- responsible for hearing, contain 90% of cochlear nerve fibers
Outer hair cells- specialized type of epithelial cells that amplify sound waves via their contractile properties
What does the stria vascularis do?
Produces endolymph and maintains its electrochemical properties
What is the blood-labyrinth barrier?
The high endocochlear potential that serves to drive positively charged ions into the hair cells down their concentration gradient. It is one of the main sites of drug entry to inner hair cells
What are otoacoustic emissions?
Retrograde movement of the basilar membrane toward the oval window and through the middle ear via the ossicles causing displacement of the tympanic membrane and therefore producing sound
How do olivocochlear efferents help protect the cochlea during intense sound?
Reduce electromotility of outer hair cells and reduce responses of inner hair cells
-also decreass basilar membrane motion
How do medial ear efferents help protect the cochlea during intense sound?
Tensor tympani m and stapedius m attenuate sounds. Bilateral response decreases transmission of sound
How do autonomic efferents help protect the cochlea during intense sound?
Regulate vascular tone in blood supply to the cochlea, arise from CN VIII (sympathetic adrenergic fibers)
What do the dorsal cochlear nuclei do vs the ventral cochlear nuclei?
DCN - integrates acoustic info with somatosensory info
VCN - begins processing temporal and spectral features of sound
What does the medial superior olivary complex vs the lateral superior olivary complex do?
MSO - generates map of interaural time differences to localize sound
LSO - generates map of interaural intensity differences to localize source of sound
Both receive excitatory (glutamatergic) input and then converge into the Inferior Colliculus
