Hearing Anatomy Flashcards
How does sound travel from the outer to middle ear?
Sound pressure → vibrates tympanic membrane → moves ossicles → levering motion of ossicles overcomes impedance mismatch between air and fluid → pushes on oval window, causing fluid in scala vestibuli to move → causes a traveling wave within the basilar membrane → moves the hair cells that sit on top of it
What causes the basilar membrane to move, and what does this movement cause?
the movement of fluid causes the basilar membrane to move
this causes movement/shearing of the hair cells which moves the streocilia on top of the hair cells which is what acts on mechanically gated potassium channels
Are inner or outer hair cells more responsible for transducing auditory input into an electrical signal?
Inner hair cells!
Responsible for 95% of transduction of auditory input into an electrical signal
What happens where sterocilia are sheared toward the tallest stereocilia?
the mechanically gated potassium channels open and an there is an influx of potassium into the hair cell which depolarizes it
What happens when stereocilia are sheared toward the shortest stereocilia?
the mechanically gated potassium channels are closed, and there is a reduction of the amount of potassium into the hair cell
What are the top of the hair cells bathed in?
endolymph
What happens when mechanically gated K+ channels open in hair cells?
influx of potassium into the cell
depolarization
opening of voltage gated calcium channels
influx of calcium triggers release of neurotransmitters onto peripheral axons of the auditory nerve
What are the physical properties of the basilar membrane?
Base = narrow, thicker, stiffer
analyzes higher frequencies
Apex = wider, thinner, floppier
analyzes lower frequencies
How does the properties of the basilar membrane affect the motion of it?
different parts of the basilar membrane are going to be displaced more or less depending on the frequency on the sound that is entering the ear
the entire basilar membrane is set in motion, but certain parts of the membrane are being maximally displaced depending on the frequency being analyzed
How does the frequency being analyzed by the BM impact the hair cells on top of the BM?
higher frequency sounds maximally impacts hair cells that are sitting on top of the base of the basilar membrane (maximal shearing)
lower frequency sound maximally impacts hair cells that are sitting on top of the apex of the basilar membrane (maximal shearing)
What is tonotopy in the BM?
The organization of structure being maintained across the BM, the hair cells sitting on top of it, and the auditory nerve cells that are underneath the hair cells
*spatial map of sound frequency information
*means to be organized by sound frequency
How do frequency levels and action potentials relate?
for low frequencies received in the basilar membrane, a small amount of action potentials are fired at a particular region designated for low frequencies and vice versa for high frequencies
because there are designated positions for low and high frequencies, the nerve position will not fire any action potentials for the contrasting frequency signal
What is Phase Locking?
when auditory nerve fibers respond in time with a particular location of the sound phase
at lower sound frequencies we have less cycles per second, and the auditory nerve fiber is able to send an action potential to correlate to a particular point
At mid range sound frequencies, there are slightly more cycles per second, so the auditory nerve fiber is only able to send an action potential for every other peak of the pure tone or every second cycle due to the limit placed on how fast a single neuron can fire an action potential
Why can’t phase locking occur for high frequency sounds?
Because of limitations in the nerve fibers physiology
relies on tonotopy for high frequency sounds instead
How does the PNS maintain information about sound intensity (loudness)?
high intensity sound is a much stronger input than a quiet low intensity sound and will cause much more displacement (more mechanical movement of the system)
