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)
What is the purpose of the vestibular system?
To help our body be aware of our body’s position in 3D space
balance
maintaining visual focus while body is in motion
What are the two subsets of the vestibular system
linear acceleration
angular acceleration
How are the saccule and utricle positioned in relation to each other and why is this significant?
Saccule and utricle are positioned at 90 degrees to one another in different planes so they can communicate with each other about side to side and front to back movement
What is the Utricle? What causes shearing of the hair cells on it? What is it important for?
a supporting cell that has hair cells pointing up at the sky
shearing of the hair cells is caused by forward and backward movement
important for transducing real world information in the forward and backward plane for linear acceleration
What is the saccule? What causes shearing of the hair cells on it? What is it important for?
Saccule is a supporting cell that has hair cells pointing in a 90 degree angle, so they are pointing out to the side
shearing of the hair cells is caused by up and down movement
allows them to transduce up and down movement for linear acceleration
What does the dividing line down the center of the utricle and saccule do?
It separates the short stereo cilia and tall stereo cilia which allows for bending in either direction
What is the gelatinous matrix
What the stereocilia are embedded in
What is the macula
what the hair cells are imbedded in and the vestibular nerve axons
What is the otoconia
if we are getting front to back movement, it responds to this movement at a different speed than the cells below them which makes extra weight for gravity to act on
What are semicircular canals designed to detect
designed to detect and transduce head rotation and angular acceleration
What are the otolith organs designed to detect?
designed to detect linear acceleration in vertical and horizontal planes
What semicircular canals are activated by rolling the head?
anterior semicircular canal activation
What semicircular canals are activated by pitching the head?
posterior semicircular canal activation
What semicircular canals are activated by yawing the head?
lateral semicircular canal activation
What is the structure of semicircular canals?
Bony semicircular canal is filled with endolymph
The bulge = the ampulla
Within the ampulla we have the hair cells which are being supported by the cristae (supporting cells)
Hair cells have tiny little stereocilia that are sticking into the cupula
Cupula is analogous to the gelatinous matrix in the satricle and utricle
It’s jello like and bendy (not solid like the bones of the semicircular canal)
Below each hair cell is a nerve fiber that can receive neurotransmitters from the vestibular nerve
How does inertia play a role in the rotation of Semicircular canals
Sudden rotational (angular) movement causes the fluid (endolymph) in the semicircular canal to lag behind the movement of the semicircular canal because of inertia
In contrast, the cupula, which is adhered to the bottom of the ampulla, moves right away with no lag
Cupula gets jammed into endolymph that is not set in motion yet
This causes bending of the cupula which causes shearing on the stereocilia that are embedded in it
The shearing results in opening of mechanically gated potassium channels, there will be an influx of potassium ions (since there is a high concentration in the endolymph that coats the structure), triggering an opening of calcium gated channels, which causes the release of neurotransmitter from the vestibular nerve
When the rotation stops, endolymph keeps moving due to inertia, bending the cupula the other direction affecting the other side of the stereocilia hair cells, and sends an action potential from the other side.
Acts as a code for angular rotation in both directions (depending on the way the cupula bends)
*movement towards the highest stereocilia causes depolarization,
movement towards the shorter stereocilia causes hyperpolarization
