Auditory System II (Signal Transduction in Hair Cells) Flashcards
What are the protein fibres called that connect potassium channels in steriocilia?
Tip links
At rest, what state are the potassium channels in on stereocilia? Is the membrane hyperpolarized or depolarized in this state?
At rest, some potassium channels are open leaving the membrane partially depolarized
What occurs when the stereocilia on hair cells bend towards the longest stereocilia?
Upward displacement
This pulls on tip links which opens potassium channels - leads to depolarization
What occurs when the stereocilia on hair cells bend away from the longest stereocilia?
Downward displacement
This slackens tip links, which closes potassium channels - leads to hyperpolarization
Overall vibration of the basilar membrane causes what?
Back and forth bending of stereocilia, leading to bursts of NT release
What NT is released onto the afferents of the cochlear nerve?
Glutamate
What occurs to allow glutamate release?
Depolarization of the membrane causes voltage-gated calcium channels to open, causing an influx of calcium
This triggers glutamate release from the hair cell onto the afferent ending of the nerve
Why does potassium flow into the hair cell?
The endolymph outside the hair cell has a high concentration of potassium, therefore when potassium channels are opened (upward displacement), potassium flows into the cell, leading to depolarization
How is pitch coded for?
Specific afferents in the cochlear nerve are activated (tonotopic map)
How is volume coded for?
Frequency of action potentials in the afferents
How are loud sounds detected?
More deflection of basilar membrane –> bend stereocilia more –> more potassium channels open –> greater depolarization of hair cells –> more glutamate is released –> more depolarization and higher frequency of action potentials in afferents
Why are very loud sounds damaging to hearing?
They can break stereocilia
What is nerve deafness and what are its possible causes? What can be done to fix this problem?
Hearing loss due to damage to hair cells
Possible causes: Drugs (aminoglycosides, antibiotics, antimitotics), inner ear infections, loud noises, diseases (e.g., Meniere’s)
Cochlear implants can be inserted to bypass normal routes of conduction and transduction - causes direct stimulation of cochlear nerve afferents
Describe the auditory pathway (starting at cochlear nerve and ending at primary auditory cortex)
Signal travels via cochlear nerve (cranial nerve VIII) to ipsilateral (same side) cochlear nuclei in brainstem –> bilaterally to the other cochlear nuclei (in brainstem) which allows for localization of sound based on difference in timing and intensity between ears –> then travels to primary auditory cortex via the medial geniculate nucleus of the thalamus (tonotopic map is maintained in the primary auditory cortex)
