Exam 2 Hearing 2 Flashcards
_________ hair cells respond to sound with both a receptor potential and a change in length.
•Motion of the cell body in response to changes in cell membrane potential may augment basilar-membrane motion, and create a cochlear amplifier.
-depolarization casues motor proteins to contact
Outer
____ hair cells produce their greatest response at a characteristic sound frequency
Inner
_____ hair cells are for protection and amplification of sound
________ hair cells are for transduction and do NOT contract
Inner
How is a hair cell depolarized?
Entry of K+ into the hair cell causes depolarization not hyperpolarization because endolymph is high in K+.
- Depolarization activates voltage-gated Ca2+ channels.
- Entry of Ca2+ triggers the release of neurotransmitter.
–Neurotransmitter activates spiral ganglion fibers.
Explain the auditory pathway
- Afferents from the spiral ganglion enter the brainstem in the auditory nerve.
- At the level of the medulla, the axons innervate the dorsal and ventral cochlear nuclei ipsilateral to the cochlea where the axons originated.
–Sound processing begins in the cochlear nuclei.
- There are multiple pathways from here on.
- All ascending auditory pathways converge onto the inferior colliculus.
- The MGN is in the thalamus.
- There is extensive feedback in the auditory pathways.
- Other than the cochlear nuclei, auditory nuclei in the brain stem receive input from both ears.
What is the systematic organization within an auditory structure based on characteristic frequency?
-_______maps are found on the basilar membrane, auditory nerve, and cochlear nucleus.
•________ maps also are found within each of the auditory nerve relay nuclei, the medial geniculate nucleus (MGN) and the auditory cortex.
Tonotopy
Explain the basic mechanisms for coding pitch
- Pitch gets encoded in the cochlea by hair cells, each of which has a best frequency.
- Each of these hair cells measures the energy in a narrow band of frequencies and encodes this measure in the nerve discharge.
- The array of hair cells provides the central nervous system (CNS) with moment-by-moment information about the frequency content of incoming sound.
- The vibration pattern of the basilar membrane along with a tonotopic arrangement of hair cells along the membrane helps to sharpen the response of the hair cells.
- Overall, this arrangement provides the CNS with the frequency spectrum of the sound signaled via approximately 30,000 nerve fibers per cochlea.
WHat are the two interrelated ways that sound intensity is coded?
Rate
Recruitment
How does rate code for sound intensity?
As sound intensity increases, the discharge rate of individual hair cells increases.
How does recruitment code for sound intensity?
•As sound intensity increases, additional receptors get recruited. Not all receptors have the same threshold.
–An auditory neuron is most responsive to sound at one frequency, called its ________ frequency, and it is less responsive at neighboring frequencies.
-it will only fire when it gets this frequency
characteristic
The louder the sound, the _____ an auditory nerve fiber fires action potentials.
Faster
Louder sounds produce movements of the basilar membrane over a greater distance. Thus, ____ neurons are activated as sound intensity increases.
More
•The main source of information about sound frequency that complements information derived from tonotopic maps is the timing of neural firing, which is called?
Phase locking
•How different sound frequencies are represented.
–At very ______ frequencies, phase locking is used
–At ________ frequencies, phase locking and tonotopy are used.
–At _____ frequencies, tonotopy is used.
1) Low
2) intermediate
3) high
Localization of sound in the horizontal plane occurs because of the ______
duplex theory of sound localization
____________ is the time difference between the sound arriving at one ear and then the other ear.
-This provides a cue to the location of sound.
Interaural time delay
(a) Sound waves coming from the right side will reach the right ear first, and there will be a large interaural delay before the sound propagates to the left ear.
(b) If the sound comes from straight ahead, there is no interaural delay. Delays for three different sound directions are shown.
_________does NOT help to localize sound when a continuous sound is emitted.
The sound is always present in both ears and there is no delay.
This sound is located by interaural intensity difference.
–The peak of the sound wave reaches one ear before the other.
–The head casts a sound shadow causing a more intense sound in one ear than the other.
•Interaural time delay
________ are sensitive to sound localization.
•Binaural neurons
Explain this image
•Binaural neurons are sensitive to sound localization.
–The figure shows delay lines and neuronal sensitivity to interaural delay.
•Localization of sound in the vertical plane is based on reflection from the _______.
pinna
