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Definition
the least amount of energy required for an average human to detect sound.
Threshold flattens out near zero. Measurement of sound pressure 0.0002 dynes/cm2 is a reference point to get threshold for a 1000Hz tone.
Threshold changes with frequency. Lower frequencies take a lot more energy to reach threshold. High frequencies also require more energy (above 5-7000Hz). |
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Definition
The decibel is a ratio measurement (log scale) for sound pressure level
Decibel= 20•log(P/PR)
Most speach is delivered between 250-500Hz or 40-50dB |
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Definition
| The outer ear is cup shaped and funnels sound waves into the ear. The cannal functions as a resonance chamber and has a resonance frequency of 3500Hz. This contributes to the fact that the lowest human threshold is around 3500Hz. The outer ear also helps to localize sound. |
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Definition
-This is where infections occur due to blocked eustachian tubes.
-3 oscicles(small bones): maleus, incus, and stapes transfer sound from tempanic membrance to the cochlea. Also, increased force by acting as a lever |
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| Discuss the transfer of energy from the tempanic membrane to the oval window of the cochlea |
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Definition
The cochlea is filled with fluid, so it takes more energy to push against it. The oscicles act as levers to increase the force applied to the oval window. Also, remember that P=F/A. The area decreases 17 times and the oscicles increase the force 1.3 times. Displacement decreases .75 times.
This helps to overcome impedence (resistance that varies with frequency). |
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Term
| Describe the anatomy of the cochlea |
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Definition
| The cochlea is a snail-like structure which contains three fluid filled chambers. These are the scala vestibuli, scala media, and the scala tympani. The basilar membrane is between the scala media and scala tympani. It contains hair cells on top of it. Reissner's membrane is between the scala vestibuli and scala media. Fluid passes through the helicatrema and connects the scala vestibuli and scala tympani which contain perilymph. The fluid in the scala media is endolymph and is more like ICF (high K). |
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| Describe what happens when the stapes hits the oval window (fluid motion) |
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Definition
| It creates a pressure wave in the scala vestibuli which pushes on the reissners membrane. The reissners membrane creates a pressure on the scale media which puts pressure on the basilar membrane. This creates pressure in the scala tympani which causes the round window to bulge. The round window goes back in to decrease pressure causing the basilar membrane to go up. Ultimately, the basilar membrane winds up moving up and down rapidly (depending on the frequency). |
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| Discuss what happens to the hair on the basilar membrane when it moves |
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Definition
| The hair cells move with the basilar membrane, but the tectorial membrane above the hair cells does not move as quickly. This causes the hair cells to bend. This causes a depolarization in the membrane potential, so they release neurotransmitter and activate the sensory neurons or the auditory nerves. |
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| Discuss the differences in the physical properties of the cochlea from the base to the apex and the effects these differences have on sound detection |
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Definition
At the base (near the stapes), the chochlea is narrow, stiff, thick, and not very compliant. This causes it to respond well to high frequency sounds.
At the apex (near the helicotrema), the cochlea is wide, thin, and very compliant. This causes it to respond well to low frequency sounds.
So, properties of the membrane determine where the hair cells will fire and those cells will encode those frequencies (high vs low). |
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Term
| Define characteristic frequency and discuss the tuning curve |
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Definition
Characteristic frequency: due to position along the cell membrane- the frequency at which the cell will fire BEST
The energy required for higher frequencies increases steeply on the tuning curve (to the R).
The energy required for lower frequences also increases, but the increase is more gradual on the tuning curve (to the L).
There is a lot of overlap, but the auditory system uses lateral inhibition to sharpen the stimulus. So, the higher you go in ther nervous system the sharper the tuning curve appears. |
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| Discuss the auditory pathway and tonotopic mapping |
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Definition
The auditory nerve is the 8th cranial nerve. Information goes to the cochlear nucleus and then travels ipsilaterally and contralaterally to the thalamus and then to the auditory cortex. (This is why a one-sided injury does not usually result in deafness)
Tonotopis organization refers to the spacial mapping of different frequencies through out the auditory system. In the brain, low frequencies are superficial and high frequencies are deep in the cortex. |
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