Audition II
Terms
undefined, object
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- An increase of 1 dB is equivalent to what kind of increase in sound pressure?
- Each dB increase means a ten-fold increase in sound pressure.
- What determines the pitch of sound?
- Its frequency.
- What frequencies of sound are audible to humans?
- 20-20,000 Hz
- At what frequency do vowels occur? Consonants? How does this explain a loss of the ability to differentiate consonants as seen in presbyacusis?
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*vowels - low frequency
*consonants - high frequency
*high frequency discrimination is one of the first things to go in presbyacusis - What is a spectrograph? How can the fundamental frequency of a sound be recognized on one?
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*a visual representation of a sound at which the energy at each frequency is depicted
*the fundamental frequency will be that one with the greatest energy - What is one of the unique functions of the pinna?
- It helps to determine vertical elevation of sound, one of the few structures to do so.
- What is the essential function of the middle ear?
- It transduces sound energy from air to liquid, while at the same time increasing the force of the vibrations to account for the greater density of fluid.
- What are the two middle ear muscles and where do they insert? What is their function?
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*stapedius - stapes
*tensor tympani - malleus
*dampen vibrations to prevent damage - What is otosclerosis?
- A proliferation of bone at the foot of the stapes which interferes with its ability to vibrate on the oval window. This causes a conductive deafness.
- Hearing aids are an effective form of treatment for what kind of deafness?
- Conductive deafness.
- Where do CN VIII fibers leave the cochlea? Where are their cell bodies?
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*at the basal turn
*in the spiral ganglia - What fluids are contained in the scali vestibuli, tympani and media?
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*scali tympani and vestibuli: perilymph
*scali media: endolymph - What separates the scali media from the scali tympani? What is located on this structure?
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*the basilar membrane
*the organ of Corti - Describe the arrangement of hair cells on the organ of Corti.
- A single row of 4,000 inner hair cells and three rows of 12,000 outer hair cells, all of which extend the length of the cochlea.
- What separates the end of the scali vestibuli with the beginning of the scali tympani?
- Helicotrema
- After a wave of pressure hits the scali tympani, how is it then detected?
- As the wave passes through the scali tympani it causes the basilar membrane to vibrate. The differential movement of the basilar membrane and the tectorial membrane causes a shearing motion on the hair cells which causes depolarization.
- What is the shape of the basilar membrane unrolled? Describe the tonotropic organization of the membrane.
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*trapezoidal, narrowest at the base and widest at the apex
*each portion is most responsive to vibration at a certain frequency - the apex to low frequency and the base to high frequency - Describe the synapses formed by the inner hair cells and those formed by outer hair cells.
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*each inner hair cell synapses with ~10 afferent nerve fibers; this is a divergent arrangement
*each outer hair cell is one of ten such cells to synapse with a single efferent fiber; this is a convergent arrangement - How does the tonotropic organization of the basilar membrane affect the sensitivity of the inner hair cells?
- Because of the tonotropic organization of the basilar membrane, each hair cell is maximally responsive to vibrations at a certain frequency (as determined by its position).
- What are otoacoustic emmissions? What is thought to be their purpose?
- They are sounds that are generated by efferent stimulation of the outer hair cells. They are thought to add 30dB to the threshold of hearing and thus sharpen frequency discrimination.
- How are different sounds coded for? What does "critical frequency" mean in this context?
- With a labeled line system: because each afferent fiber is associated with a single hair cell, activity on this nerve signals sound at the frequency of that hair cell. This is the "critical frequency" of that nerve fiber.
- Why are afferent fibers unable to fire with each vibration of a high frequency sound?
- The refractory period of the nerve prevents firing above a certain pace.
- Cochlear implants are an effective treatment for what kind of deafness? Why is this possible?
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*sensorineural deafness
*typically the hair cells are defective but the nerve fibers are fully functional; also the tonotropic organization of the nerve makes it possible - Describe briefly how cochlear implants work.
- An external device receives soound and converts it to an electrical signal. This signal is passed through a multi-array electrode that directly stimulates the cochlear fibers of CN VIII. The tonotropic organization of the fibers makes this possible.