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SLHS 380 Exam 1 Review
Terms in this set (62)
How does the pinna modify sounds upon reaching the ear drum?
High frequency tones have different directional spectral patterns
What do inner hair cells do in response to a 2000 Hz tone?
Depolarize at a rate of 2000 times per second
Base of cochlea responds to:
HIGH FREQUENCIES (stiffer)
Apex of cochlea responds to:
LOW FREQUENCIES (floppier)
MANY type 1 afferent nerves connect to:
ONE inner hair cell
ONE type 2 afferent nerve fiber connects to:
MANY outer hair cells
Perilymph is found where?
Scala Vestibuli, Scala Tympani
Endolymph is found where?
Produces endolymph, maintains endocochlear potential. Also called the battery
Resting potential of Scala Media
Resting potential of inner hair cells
Major functions of outer hair cells:
Amplify soft sounds, sharpen frequencies
Major functions of inner hair cells:
Sending auditory signals to the brain
Stapes footplate connects to the ______ window
How does the buckling motion work?
Curvature of the ear drum causes the malleus to move with 2x the force
What structure does the organ of corti sit on?
Loudness is encoded by the auditory nerve by:
number of spikes
What information is provided by a tuning curve?
Characteristic frequency, bandwidth, threshold of characteristic frequency. DOES NOT INCLUDE: spontaneous rate fibers
High spontaneous rate fibers have ____ thresholds
Low spontaneous rate fibers have ____ thresholds
Boost of concha resonance:
10 dB at 5,000 Hz
Dynamic range for a single auditory nerve fiber is:
Dynamic range of hearing
range of hearing between threshold and loudness discomfort level; range of usable hearing. 0-120 dB
Potential differential across top of hair cells vs. inside of hair cells?
The traveling wave on the BM always goes in what direction?
base to apex (stiff to loose)
Boost from ear canal resonance:
~13 dB @ 2500Hz
Primary function of middle ear
overcoming impedance mismatch
Mechanisms used to overcome impedance mismatch
lever action, buckling motion, area-ratio difference
+25 dB - amplification is provided because of the difference in the area of eardrum in comparison to area of stapes footplate
+2 dB - difference in length between the malleus and the incus.
Buckling motion (catenary area effect)
+6 dB - the TM is curved, which allows for the energy to be focused on a smaller point
What is the maximum peak shown from a middle-ear transfer function?
33 dB at 1000-2000 Hz
Why is it important that the oval window alone be stimulated by the sound via stapes, but not that both the oval window and the round window be stimulated at the same time?
No energy would pass through to the inner ear, as there would be no vibration and the fluid would not move
What is the role of middle-ear muscles?
Tense/contract to protect the ear from loud sounds by shifting the frequency lower. More effective for low frequencies (<2000 Hz) and longer sounds
What is the role of middle-ear ligaments?
Hold the ossicles in place for support and stabilization.
What's the primary function of the Auditory (Eustachian) Tube? What are the major consequences of blocking the tube?
The eustachian tube equalizes pressure on both sides of the eardrum. Blocking the tube will cause some hearing loss and discomfort.
What's the typical length in cm of a human cochlea (uncoiled)?
How many turns of the cochlea
Which scala inside the cochlea houses the celias of the hair cells?
Contains endolymph and organ of corti. Has a high concentration of K+ ions. Resting potential of +80 mV
Scala Vestibuli and Scala Tympani
contain perilymph, have a charge of 0 mV, have a high concentration of Na+ ions
How is sound organized on the basilar membrane?
Tonotopically. Higher frequencies are mapped at the base and lower frequencies at the apex
Which two membranes sandwich the hair cells?
Tectorial and Basilar Membranes. Tectorial attached to the cochlear hair cells on top, and the basilar on the bottom.
What's the resting potential inside hair cells?
During sound stimulation, what sort of relative motion of the two membranes leads the stereocilia to bend?
Basilar membrane moves / slides and the tectorial membrane stays in place causing the stereocilia (on top of hair cells) which is connected to, to bend.
What is the primary function of the stria vascularis?
Acts as a battery, maintains endolymphatic potential. Source of endocochlear potential
The relative motion between the tectorial membrane and the basilar membrane makes hair cell cellias to bend, which further leads to these actions with OHC, and these actions with IHC
Shearing/movement. Influx of endolymph depolarizes hair cells, OHC will contract
and expand, IHC will send signals to AN.
Which of the cochlear potentials is present in the absence of acoustic stimulation
+80 mV--potential of Scala Media
What values are the three resting electrical potentials in mV inside the hair cells (-60 or -40 mV), in scala media (+80 mV), and in scala Vestibule and scala Tympani (0 mV)?
The vast majority of the auditory afferent nerves are:
Type 1 fibers connect to:
INNER hair cells
What information can be obtained from a rate-level function
dynamic range, threshold, saturation level
How are the primary AN fibers classified according to their spontaneous response rate?
Low spontaneous rate (LSR): <0.5 spikes/sec ⇒ high threshold
Med spontaneous rate: 0.5< SR< 18 spikes/sec ⇒ med threshold
High spontaneous rate: >18 spikes/sec ⇒ low threshold
How does the neural-response threshold depend on the spontaneous response rate?
Because spontaneous rate has activity in the absence of sound, the neural fibers are active. They are not silent. So based on spontaneous rate, we define the threshold.
Threshold is the lowest level (in dB) at which the neural discharge rate increases by 5 spikes/sec above the spontaneous threshold.
What does a tuning curve show? (or, what are the x and y axes of the plot showing a TC?) How are TCs measured? What information can we gather from a TC?
- Tuning curve shows the basilar membrane resonance. The x-axis is best frequency and the y-axis is spikes/sec. To measure, electrodes are fixed to a particular fiber and the fiber resonates a particular frequency. At this frequency the fiber is most responsive and stimulates the fiber to a particular rate.
- On the tuning curve we can determine best frequency, threshold and 3-db bandwidth.
What is the 'dynamic-range problem' in hearing?
Auditory nerve fibers have a dynamic range of 30dB while we can hear a dynamic range of 120dB. This mismatch is called the dynamic range problem since it needs 2 mechanisms in order to correct this problem.
How does the auditory system overcome (or compensate for) the dynamic-range problem?
1. Individual neurons with different spontaneous rates have different threshold (high SR= Low TH ; Low SR= High TH) working together they cover a wider range of sound level
--AN fibers with different thresholds work together to cover large range of stimulus level (extend the dynamic range
2. Individual neurons with different best frequencies can work together to cover a wide range of sound level
--AN fibers with different best frequencies work together to extend the dynamic range
What is the basis for the temporal coding of stimulus frequency (temporal theory)?
Low frequency tones excite neurons and they fire at regular intervals as multiples of the tones period. The ability to phase locking is the basis of temporal coding. Peaks are locked to a particular phase, period and frequency can be determined from the time intervals.
In a two-tone suppression, describe what happens to the neural response to a probe tone when a second tone (suppressor) is introduced at an adjacent frequency
One tone reduces or cancels the other when it falls into the shaded region of
frequency and intensity.
What is the significance in auditory function of two-tone suppression?
Secondary mechanism for auditory masking.
Which type of histograms of AN discharge shows that the neural activity can follow roughly the temporal variation of the stimulus amplitude?
Post stimulus time histogram.
List six pieces of information that can be observed in a PST histogram in response to a steady tone.
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