Chapter 13: Audition

How does a wave travel through the inner ear?

A standing wave starts at the cochlear base. As it moves to the cochlear apex, the surface of the basilar membrane fluctuates, it pushes the hair cells up towards the tectorial membrane.

How can we locate sound in space?

By calculating the difference in the two waves.

Where does hearing begin?

Hearing begins in the inner ear

How does the MSO compute the location of sound?

It does this by computing the time difference between the two waves. For example, when a speaker is being played, it will reach both the left and right ears. Say it enters the left ear first. The AP will travel towards the MSO, and will reach the left ear leading neuron. This is a longer path to neuron E. The sound reaches the right ear a little later, and the AP begins to travel toward the MSO. This is a shorter pathway to neuron E. The AP converge on a MSO neuron that responds most strongly if their arrival is coincident.

How does hyperpolarization and depolarization of the stereocilia happens?

It happens with the pushing up of stereocilia against the tectorial membrane. Hyperpolarization closes the calcium channels, and no AP is caused. Depolarization opens Ca+ and K+ channels, having a depolarization of the cell, releasing NTs.

How do we hear?

Sound waves hit the tympanic membrane and travel down the malleus, the incus, and the stapes, and then enter the inner ear at the base of stapes in the oval window. It's hard to take air waves and translate them to liquid waves. To do that, you focus the force in a small area.

What makes a sound wave loud?

The amplitude.

What is the audible spectrum? What is the optimal hearing?

The audible spectrum is anywhere from 20Hz to 20kHz. Our optimal hearing is at about 3kHz.

What is the auditory pathway?

The auditory nerve enters the rostral medulla and ascends to the mid-pons. It stops at the superior olive, where it branches bilaterally. It ascends the nucleus of lateral lemniscus and stops in the inferior colliculus at the caudal midbrain.

What is phase lock? q

The auditory nerve will tend to fire at a particular phase of a stimulating low-frequency tone.

How does the frequency tuning of basilar membrane work?

The basilar membrane is tuned to different frequencies. This is called the frequency-encoding by labeled line. Relative dB of sound is required to elicit a response from the background to the auditory fibers.

What is the physical properties of the cochlea?

The cochlear base is narrow and stiff and is tuned for high frequencies. The cochlear apex is wide and flexible and is tuned for low frequencies.

What is the external ear?

The external ear is the outer part of the ear. It is designed to collect sound waves and focus them on the ear drum. It filters sounds of different pitches to provide cues about the elevation of sound source.

What makes a sound pitch high?

The frequency.

What is the kinocilium?

The kinocilium is the tallest stereocilia.

What is the middle ear?

The middle ear is designed to overcome the impedance of the inner ear so that the airborn soundwaves get transferred into the middle ear. Impedance is P/DV, in which P is the pressure and DV is the displacement in volume. In order to make up for less impedance in air than there is in water, then there must be a larger pressure on the ear drum over a smaller area.

What parts of the ear is there?

There is the external ear, the middle ear, and the inner ear.

How are stereocilia arranged?

They are tiered and bundled by tip links. The tip links function as the gating mechanism that opens the K+ channels. When the channels open, you have an influx of K+ into the stereocilia that leads to the depolarization of the cell.

What is tonotopy?

Tonotopy is the frequency mapping of the primary auditory cortex that have different areas that correspond to the different areas in the cochlea.

Why is there a rush of K+ into the stereocilia? Doesn't K+ usually leave?

Unlike most fluid, the fluid that fills the media has a high concentration of K+. Because so, the K+ equilibrium potential is a little higher than we're used to, which causes the influx of K+ ions.

Above 1000Hz, pitch is no longer encoded in the oscillations in Vm of the hair cell. How do we hear and distinguish frequencies greater than 1000Hz?

We have special systems, called the frequency tuning of basilar membrane and the frequency tuning of auditory nerve.

How can you differentiate the hyperpolarization and depolarization of the stereocilia?

You can tell whether the displacement of the hair cells is either towards or away from the kinocilium. Towards kinocilium: Depolarization Away kinocilium: Hyperpolarization. This has to do with the fact that displacing towards the tall end opens them, but when you are towards the small end it closes the channels, but not enough to make a significant difference.

Which of the following statements about lemniscal and collicular sound processing is false? a. The different acoustical cell types seen in the inferior colliculus were present in the earlier cochlear nuclei, but had not been formed into a topographic map. b. Unlike the physical mapping of the visual world onto the retina, the auditory "space map" in the inferior colliculus is purely a construct of the brainstem's processing of auditory information. c. Certain collicular neurons respond preferentially to frequency-modulated sounds. d. Certain collicular neurons respond preferentially to sounds of a fixed duration. e. The monaural pathway connects the cochlear nucleus to the midbrain via the nuclei of the lateral lemniscus.

a. The different acoustical cell types seen in the inferior colliculus were present in the earlier cochlear nuclei, but had not been formed into a topographic map.

Which of the following statements about the functioning of cochlear implants (CIs) is false? a. They are designed to induce electromechanical pressure waves within the cochlear fluid. b. They require an electrical connection from an implanted stimulator to a cochlear electrode array. c. They provide tonotopic delivery of electrical signals along the length of the cochlea. d. They require an auditory signal processing device that decomposes sounds into component frequencies. e. They electrically stimulate residual hair cells and/or primary auditory afferents.

a. They are designed to induce electromechanical pressure waves within the cochlear fluid.

Which of the following most depends upon the utilization of bilateral auditory information? a. Frequency discrimination b. Sound localization c. Distinguishing pitch from timbre d. Encoding of speech sounds e. Detection of very faint sounds

b. Sound localization

_______ gives rise to tonotopy along the cochlea. a. The changing width and stiffness of the tectorial membrane b. The changing width and stiffness of the basilar membrane c. The speed at which sound waves propagate along the length of the cochlea d. The changing mechanical properties of the cochlear wall along the length of the cochlea e. The increasing density of the cochlear fluid along the length of the cochlea

b. The changing width and stiffness of the basilar membrane

Which of the following statements about sensory transduction by hair cells is false? a. Bending of the cilia toward the longest cilium produces depolarization. b. The electrical activity initiated by the tip links is transmitted to the vesicular release sites along microtubules that undergo voltage-dependent rearrangements. c. The dynamic range of the hair cell for reporting mechanical events is determined by the degree to which mechanical deflection can result in changes in membrane potential. d. Hair cells are presynaptic to second-order sensory neurons. e. The firing of action potentials in second-order sensory neurons can be either up- or down-regulated, depending on the direction in which the bundle of cilia (of the afferent hair cell) is bent.

b. The electrical activity initiated by the tip links is transmitted to the vesicular release sites along microtubules that undergo voltage-dependent rearrangements.

Otoacoustic emissions a. were predicted by Von Békésy's model of cochlear mechanics b. are a means of assessing hearing in newborn babies c. originate exclusively from inner hair cells d. are missing from the ears of rock musicians suffering from tinnitus e. All of the above

b. are a means of assessing hearing in newborn babies

The auditory hair-cell bodies are embedded in the a. tectorial membrane. b. basilar membrane. c. tunnel of Corti. d. spiral ganglion. e. oval window.

b. basilar membrane.

Which of the following is the primary function of the three bones in the middle ear? a. Selective transmission of high-frequency sounds b. Selective transmission of low-frequency sounds c. Amplification of sound pressure waves to increase auditory sensitivity d. Dampening sound pressure waves to prevent damage to the ear e. Facilitation of fluid drainage from the Eustachian tube

c. Amplification of sound pressure waves to increase auditory sensitivity

Which of the following is not a function or operating feature of the outer ear? a. Boosting sound pressure level as it enters the ear b. Filtering sound in an adaptive manner based on source elevation c. Directing different frequencies of sound to specific cochlear locations d. Optimally transmitting sounds in our range of vocalizations e. Boosting frequencies by means of passive resonances

c. Directing different frequencies of sound to specific cochlear locations

Which of the following is not representative of the computations performed in auditory cortex? a. Specializations for communications between conspecifics. b. Use of orthogonal frequency-auditory dominance maps. c. Processing in distinct "auditory object" (ventral) and "auditory location" (dorsal) information streams. d. Specializations for detecting temporal sequences of sounds. e. Lateralization of processing for speech, music and environmental sounds.

c. Processing in distinct "auditory object" (ventral) and "auditory location" (dorsal) information streams.

In order to increase the decibel measurement of a sound, one would have to alter its wave a. form. b. phase. c. amplitude. d. frequency. e. length.

c. amplitude.

Which of the following is a valid distinction between hair cells that operate at 500 Hz and those that operate at 5000 Hz? a. The 500 Hz cells make use of different ions in the transduction processes. b. The 500 Hz cells make use of different tip link proteins to confer frequency specificity. c. The 500 Hz cells provide a phase-locked auditory signal, whereas the 5000 Hz cells do not. d. The 500 Hz cells fatigue far more readily than the 5000 Hz cells do. e. All of the above

d. The 500 Hz cells fatigue far more readily than the 5000 Hz cells do.

Cells with pronounced selectivity for specific combinations of sound frequencies are first found in the a. ventral cochlear nucleus. b. nuclei of the lateral lemniscus. c. inferior colliculus. d. medial geniculate complex. e. lateral and medial superior olives.

d. medial geniculate complex.

In which of the following ways is the mechanism of hair-cell transduction distinct from sensory transduction mechanisms that occur outside the ear? a. Potassium influx from the endolymph depolarizes the hair cell. b. Potassium efflux into the perilymph repolarizes the hair cell. c. Calcium and calcium-activated potassium channels contribute to electromechanical resonance. d. The two domains of the hair cell operate, in effect, as two distinct Nernstian compartments. e. All of the above

e. All of the above

Research into the biology of those stem cells that generate cochlear hair cells during development could be valuable because a. hair cells are quite sensitive to damage. b. humans begin life with a relatively small number (~15,000 per cochlea) of hair cells. c. mammalian hair cells do not regenerate themselves. d. understanding the basic mechanisms of hair-cell development may suggest therapeutic approaches. e. All of the above

e. All of the above

Which of the following is not a cause of hearing loss? a. Acoustic trauma b. Infection c. Ototoxic drugs d. Aging e. All of the above are causes of hearing loss.

e. All of the above are causes of hearing loss.

In which of the following brain regions are the intensities (not the phases) of impinging sound waves compared in order to determine the location of sound sources? a. Cochlear nucleus b. Inferior colliculus c. Medial geniculate complex d. Medial superior olive e. Lateral superior olive

e. Lateral superior olive

Which of the following statements about auditory nerve fibers is false? a. Afferent fibers receive input from inner hair cells. b. Efferent fibers innervate the three rows of outer hair cells. c. The characteristic frequency of the hair cells varies systematically along the cochlear axis. d. The higher frequency fibers can respond well to stimuli at frequencies in the 10 to 20 KHz range. e. The lower frequency fibers have a sharp tuning peak plus a separate extended hump.

e. The lower frequency fibers have a sharp tuning peak plus a separate extended hump.

Tones that are an octave apart are perceived to be similar or sound "the same" because a. it is easier for the brain to process sounds and tones if groups of them sound similar. b. of periodic resonant frequencies within the cochlea. c. such octaval relationships commonly occur in the realm of environmental noise. d. the octave is the most compact representation of auditory stimuli. e. of reasons that we seem far from understanding.

e. of reasons that we seem far from understanding.