Section 1 Flashcards
What is the angle that the pinnae project outwards at?
15-35 degrees
How big is the ear canal?
25-35mm long
5-7mm in diameter
What is the function of the OHC?
To increase fluid disturbance and add energy into the cochlea. The IHC can respond to soft sounds if the OHC disturb the fluid enough
What are OHC responsible for?
OHC are tuned for low sound thresholds (<40dB) and responsible for sharp tuning/fine frequency discrimination
What is the effect of Prestin Motility?
It increases the fluid disturbance inside scala media and increases the displacement of the BM to create a shearing force for inner hair cells
What is Prestin Motility?
When the OHC is depolarized, it activates the prestin in the cell walls and causes the cell to expand and contract, stretching at the rate the stereocilia are moving
What is Place Theory?
The way that the auditory system codes frequency corresponds to the place on the BM where it is moving/resonating the most
What is the Pars Tensa?
-The “effective area” of the tympanic membrane
-It vibrates more when sound hits it and is a better transmitter of sound
-Radial and spiral fibers create its stiffness
-Middle layer of the TM exists in Pars Tensa, but Pars Tensa exists outside of it
What is the area of the Pars Tensa?
55mm^2
What 3 things do the middle ear structures do to amplify sound?
1.) Area difference between the TM and the stapes footplate17:1 ratio of pressure (High Heel Shoe Effect) (25dB)
2.) The level action of the ossicles (2dB)
3.) The buckling action of the TM (6dB)
What are the 5 structures of the Head Related Transfer Function (HRTF)?
1.) Head
2.) Neck/Torso
3.) Pinnae
4.) Concha
5.) External Auditory Canal
What are 3 important structural/mechanical characteristics of the basilar membrane?
1.) Narrower at the base and wider at the apex
2.) Stiffer at the base and less stiff at the apex
3.) Attached differently at the base (spiral ligament) compared to the apex (osseous lamina)
What does the tensor tympani do?
-Negligible role in activating with loud sounds
-The muscle contracts and impacts the ability of the malleus to make movements to the incus and stapes
What is the acoustic reflex?
-Triggered after 100ms
-At 80dB, the stapedius muscle contracts and pulls the stapes footplate away from the oval window to create a less intense fluid disturbance
-At 140-150dB, the footplate starts to rock rather than have a piston-like movement to create uneven/less pressured fluid disturbance
What are the 3 layers of the tympanic membrane and what are they made of?
1.) Outer layer»_space; skin
2.) Middle layer»_space; connective tissue
3.) Inner layer»_space;mucus membrane
How are stereocilia shaped or grouped together on OHC?
~150 on OHC
V-shaped
3 rows (short, medium, tall)
Tip links and cross links
How are stereocilia shaped or grouped together on IHC?
~50 on IHC
Bowl shaped
1-2 rows
Where does Prestin Motility take place?
OHC
How are afferent and efferent fibers synapsed?
-Both afferent and efferent synapse directly to OHC
-Afferent fibers synapse directly to IHC
-Efferent fibers synapse to the afferent fibers in IHC
What were the 2 problems with von Bekesy’s experiments with hair cells?
1.) Limited microscopy and he had to put 90dB in to see any movement of the IHC
2.) He used cadavers and would only be able to see the cochlea without OHC.
What is a tuning curve?
-The least amount of energy to give to a cell to make it start firing
-The level of sound against the frequency of the sound to find the cell’s favorite frequency
How is an OHC shaped?
~25 microns
Cylindrical Shape
Nucleus displaced more toward the bottom
Mitochondria on cell walls and at the bottom of the cell
~150 stereocilia
How is an IHC shaped?
~35 microns
Flask/Beaker shape
Nucleus in the middle
Mitochondria spread throughout
~50 stereocilia
What is the role of the Stria Vascularis?
-The blood and metabolic supply for the cochlea
-Provides K+ and Ca2+ ions that makes the endolymph super highly charged (+80mV)
