Unit 2 part 2 (Auditory system) Flashcards Preview

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Flashcards in Unit 2 part 2 (Auditory system) Deck (18):

Sound perception

pressure wave --> sound;
- wavelength (frequency/pitch)
- power/energy of waves (intensity/loudness)


Intensity - quantification

intensity sensitivity range for humans: 12 orders of magnitude
--> Intensity (I) = measured pressure/SPLo (a ratio)
measured in decibels (dB)
-- range is 0 - 120, change in 20 = x10 increase
* intensity varies depending on frequency of sound


3 mechanisms of frequency selection in hair cells

1. frequency separation by basilar membrane
2. morphological specializations of individual hair cells
(stereocilia near apex = longer than those near base)
3. Cochlear Amplifier: adjusts sensitivity of inner hair cell
*uses somatic motor (by outer hair cells)


Somatic motor (for cochlear amplifier)

cell bodies of outer hair cells change size in response to membrane potential changes;


frequency encoding

1. place-coding:
specific axon only carries info from one location on BM --> will carry only signals re: that frequency
2. phase-locking:
axon signals in synchrony with cycles that are multiples of the sound



the sensation of frequency of sound waves.
human range: 20-20,000 Hertz


External Ear parts

cavity open to air environment; Collects sound from environment.
1. pinna
2. External auditory meatus
3. Tympanic membrane (border to middle ear)


Middle Ear

Semi-closed cavity (open when Eustachian tube = open);
transfers sound energy from air to liquid.
1. Ossicles (malleus, incus and stapes)
2. round and oval windows
3. Tensor tympani and stapedius muscles
4. Eustachian tube


Inner Ear

completely closed cavity;
* where sound energy is converted to neural signal.
1. membranous labyrinth (sacs filled w/ fluid)
2. cochlea (for hearing and vestibular f(x))


Cochlea structure and function

3 scalae coiled 2.5 times; IN temporal bone, only partially rigid.
1, 2. Scala vestibuli and tympani
3. Scala media;
selectively responds to sound by frequency (in continuum along length)


organization of the 3 scala

(in cochlea)
- scala vestibuli and tympani both filled with perilymph; communicate w/ each other at apical end.
- scala media in middle, filled w/ endolymph,
*contains organ of corti
(vestibuli//Reissner's membr//media//basilar membrane//tympani)


organ of corti

sits on basilar membrane in scala media, runs length of cochlea;
w/ outer and inner hair cells --> stereocilia flush against tectorial membrane;
* stria vascularis = endothelium
O of C= where nerves for auditory sensation get signals from


stria vascularis

the highly vascular epithelial layer on lateral side of organ of corti;
- secretes endolymph
- regulates [K+]


innervation pattern of hair cells

Afferent: Outer: ~10 hair cells per axon
Inner: 1 hair cell per 10 axons
Efferent: signals from superior olivary nucleus to aud. hair cells


Efficiency of sound transfer in middle ear comes from:

total increase in amplitude in middle ear = 60-70%
- ossicles as levers: increase 3-5 dB
- TM much larger than oval window size (25:1) --> increase 30 dB


Basilar membrane

moves in response to pressure wave along cochlea,
* mechanically specialized so that BM responds to different (specific) frequencies in gradient along length
--> stiff at base: high frequencies
--> wide and flexible at apex: low frequencies


hair cell function

- base of hair cells gives/receives aff/eff neural signals
- stereocilia cause...
a) depolarization if displaced toward longest cilia
b) hyperpolarization if displaced toward shortest cilia
* degree of displacement matches size of signal


Mechanical Electrical Transduction (MET) Channels

process of de/re-polarizing Hair Cells for auditory sensation.
* endolymph = rich in K+; stereocilia cytoplasm = low in K+; perilymph = lowest in K+
1. tension from tip links opens K+ channels in stereocilia
--> HC depolarizes, AP sent down axon
2. -> open volt-dep./Ca-dep. K+ channels in hair cell
--> K+ leaves HC into perilymph => REpolarize cell (QUICK!)