Unit 2A (study cards) Cochlear Physiology Flashcards
What is the traveling wave?
TRAVELING WAVE (Basilar Membrane)– Near the base of the basilar membrane, depending on the frequency, there can be a space where the membrane isn’t vibrating at all (and vice versa). This is due to the characteristic frequencies of the basilar membrane.
–>Certain frequencies cause vibration at certain places in the Cochlea, and based on that, the characteristic places on the basilar membrane respond to that vibration.
–>Shapes of the cochlea are indicative of our response to the sound. Our brain has the ability to use that information (shape) to help it recognize the amt. of Hz being input.
Dancing Queens of the Cochlea
Outer hair cells
Electrophysiology
refers to the study of electricity inside the body
Electricity
the flow of charge particles/ions
Potential/Voltage
the ability of that flow
Endocochlear potential
+80 charge ions Endolymph fluid
*HIGH IN POTASSIUM and positive
Take a look at the Endolymph fluid (high + charge) inside of the Scala Media.
–>The potential of the Endolymph fluid in the Scala Media is the endocochlear potential
Hair cells (potential)
-70 in OHC
-40 in IHC
*HIGH IN CHLORINE and negative
Quick Transfer
Depolarization
+80 –> -70/-40
This big difference is what gives us the ability for QUICK TRANSFER of electricity from one place to another place. (electricity is the most important thing when it comes to sending signals from somewhere in our body to somewhere else in our body) –>
DEPOLARIZATION: positive potassium from the endolymph rushes into the hair cell. (electrical charge of the cell is changing - no longer a polar difference between two environments). –>
NEUROTRANSMITTER RELEASE: as neurotransmitters release they rush out of bottom of a hair cell and match with synapases at the bottom.
What is the Cochlear Amplifier?
The outer hair cells in movement are the Cochlear amplifier.
OHC Create the COCHLEAR AMPLIFIER
It gives us a 50-60 dB increase in how loud something sounds to us (allows us the ability to determine a sound at my personal characteristic frequency and a sound that is a little bit off (important for precision within music, per say).
increases the intensity of quiet sounds that come in
improves ability to distinguish btwn. frequencies
Cochlear Synaptopathy
Cochlear synaptopathy is the loss of synapses from the inner hair cells (they had difficulty hearing background noise). The neurotransmitter that is released (glutamate) in response to a loud sound is toxic to cells. So, when we release a lot of glutamate in response to loud noise, it causes the death of many synapses. The death of those synapses resulted in a reduced input from the inner hair cells up to the brain which leads to issues processing speech.
Tonotopic Organization
The auditory system is set up in a way where place corresponds to different tones/responses to different frequencies organized accotding to location along the basilar membrane..
The tonotopic organization of the cochlea results primarily from the fact that the basilar membrane is narrow at the base and wide at the apex.
Hyperpolarization
a reduced ability for a cell to respond to a signal while it is recovering from the last time it responded (it becomes extremely negative) During this time, it would be very hard for a cell to respond to an incoming stimulus (refractory period).
bending of the Stereocilia towards the Modiolus.
Depolarization
Depolarization happens as a result of the quick transfer of electricity from positively charged potassium ions in the endolymph fluid within the scala media to the negatively charged chlorine ions in the outer hair cells in the cochlea. As these positive ions rush into the negative ions in the hair cell, there is a change in electrical charge (no longer a polar difference between the two environments). Then, there is a neurotransmitter release as they rush out of the bottom of the hair cells to match with the synapses. These signals are sent to the brain and results in what we know as hearing sound.
Deflection of the Stereocilia away from the Modiolus.
Shearing Force
when sound waves cause a relative movement between the basilar membrane and the tectorial membrane within the cochlea, that force acting on the Stereocilia that makes them bend is called shearing force.
shearing force assumes that edges of the basilar membrane cannot move. –> this bending then triggers the opening of ion channels, generating an electrical signal that is interpreted as sound by the brain.
Cochlear Microphonic
The cochlea is a transducer and because it resembles the actions of a microphone (converting pressue waves from speakers mouth into electrical current), it is called this.
It is the result of changes in polarization from the back and forth bending of the cilia.
Alternating current receptor potential due to outer hair cells, follows “wiggles” of stimulus.
Loudness Recruitment
the abnormally large increase in loudness as intensity is increased and is suggestive of a lesion in the cochlea.
What happens when Stereocilia are deflected away from the Modiolus?
This is what is known as depolarization.
- Deflection Stretches tip links
- this causes “trap doors” on the stereocilia to be open more of the time.
- Ions diffuse into the hair cells
- the hair cells to release neurotransmitter
- this increases probability of neural firings.
Tuning Curve
How much stimulus is needed to get a particular response from the basilar membrane, a hair cell or a neuron, graphed as function of frequency.
Basilar Membrane tuning curve
how much sound (at
each frequency) is needed to get a fixed amount of
displacement of basilar membrane
Hair Cell tuning Curve
how much sound (at each
frequency) is needed to get a fixed amount of
receptor potential in the cell.
Neural Tuning Curve
how much sound (at each
frequency) is needed to get a particular neural firing
rate- Therefore, it is also called an “iso-rate curve.” V-
shaped, similar to the basilar membrane tuning curve.
Traveling Wave Envelope
the curve that outlines the maximum amplitude of a traveling wave at each point along its path
Davis Battery Model
explains how the deflection of stereocilia regulates ion flow in the hair cells.
