Chapter 9.3 Sound Transmission

Question 1

What happens to the tympanic membrane and oval window when the amplitude of a sound wave is increased?

Answer 1

The tympanic membrane and oval window move farther in and out with each pressure fluctuation, resulting in a larger bulge in the vestibular canal.

Question 2

How does the movement of the tympanic membrane and oval window affect the cochlear partition?

Answer 2

The increased movement of the tympanic membrane and oval window causes the cochlear partition to move farther up and down, resulting in more forceful shearing of the tectorial membrane across the organ of Corti

Question 3

How does the amplitude of a sound wave affect the process of hearing?

Answer 3

An increase in the amplitude of a sound wave leads to greater movement of the tympanic membrane and oval window, resulting in increased movement of the cochlear partition, hair cell stimulation, neurotransmitter release, and auditory nerve activity, ultimately contributing to the perception of a louder sound.

Question 4

How does the Cochlear Partition respond to high frequencies?

Answer 4

High frequencies cause the largest displacement of the cochlear partition closer to the oval window, near the base of the cochlea.

Question 5

How does the Cochlear Partition respond to lower frequencies?

Answer 5

Lower frequencies cause displacement of the cochlear partition farther away and nearer the apex of the cochlea.

Question 6

What is the Place Code for sound frequency?

Answer 6

The Place Code refers to the way in which different frequencies (or pitches) of sound are processed in different locations along the cochlea.

Question 7

What is cochlear tuning to frequency caused by?

Answer 7

Differences in the structures of the basilar membrane along the length of the cochlea

Question 8

How does the thickness and flexibility of the basilar membrane vary along its length?

Answer 8

The basilar membrane gets thinner and wider along its length, with thicker and stiffer regions near the base and thinner and more flexible regions near the apex.

Question 9

How does the basilar membrane separate frequencies of sound?

Answer 9

The basilar membrane, with higher frequencies (faster) affecting the narrower and stiffer regions near the base more, and lower (slower) frequencies causing greater displacements in the wider and more flexible regions near the apex of the cochlea.

Question 10

How does the timing of stimulation differ for high frequency and low-frequency regions along the basilar membrane?

Answer 10

High-frequency regions (near the base) are stimulated earlier than low-frequency regions (towards the apex) because the travelling wave takes time to travel down the basilar membrane, with faster displacement near the base where the basilar membrane is narrower.

Question 11

What are Afferent Fibers?

Answer 11

Neurons that carry sensory information from the inner ear to the central nervous system (CNS).

Question 12

What are Efferent Fibers?

Answer 12

Neurons that carry information from the CNS to the periphery, including the outer hair cells in the inner ear.

Question 13

What is the function of Efferent Fibers in the auditory system?

Answer 13

Efferent fibers play a special role in determining what kind of information is sent to the brain by afferent fibers, helping to regulate and modulate auditory signals.

Question 14

What provides most of the info into the brain via AN fibres?

Answer 14

Inner hair cells

Question 15

What is the relationship between AN fibers and frequency selectivity?

Answer 15

Responses of individual AN fibers to different frequencies are related to their place along the cochlea, showing frequency selectivity.

Question 16

When is frequency selectivity clearest in AN fibers?

Answer 16

Frequency selectivity is clearest when sounds are very faint, at very low intensity levels.

Question 17

What is a Threshold Tuning Curve?

Answer 17

Graphical representation that shows the minimum stimulus intensity required for a neuron to respond

Question 18

What is Neuron’s Characteristic Frequency?

Answer 18

Neuron’s characteristic frequency refers to the frequency to which a particular auditory fiber is most sensitive, increasing the neuron’s firing rate at the lowest intensity

Question 19

How do Outer Hair Cells influence the sharp tuning of Inner Hair Cells?

Answer 19

Outer hair cells lengthen and contract in response to electrical potential changes, causing specific stiffening of parts of the cochlear partition and making inner hair cells more sensitive to stimuli at specific frequencies, thus influencing their sharp tuning.

Question 20

What sounds do Outer Hair Cells create that audiologists use to diagnose hearing?

Answer 20

Outer hair cells create otoacoustic emissions, which are used by audiologists as a diagnostic tool for hearing assessment.

Question 21

How do Outer Hair Cells improve sensitivity and frequency selectivity?

Answer 21

Outer hair cells in the inner ear improve sensitivity and frequency selectivity through their ability to change their length in response to sound stimuli, amplifying soft sounds and enhancing the fine tuning of the cochlea’s frequency response.

Question 22

What happens to nerve fibers in response to a low intensity sine wave tone of a certain frequency?

Answer 22

Some nerve fibers increase their firing rates while others continue to fire at their spontaneous rates.

Question 23

How does the brain interpret the pattern of firing rates across nerve fiber?

Answer 23

The brain uses the knowledge of which nerve fibers have characteristic frequencies to determine the frequency of any tone within the range detected by the human cochlea.

Question 24

How does the rate of neural firing in an AN Fiber change when energy is introduced from nearby frequencies?

Answer 24

The rate of neural firing for the first tone decreases, which is known as two-tone suppression, when a second tone of slightly different frequency is added.

Question 25

How does the selectivity of AN fibers change at higher intensities?

Answer 25

[Answer] At higher intensities, AN fibers become much less selective about the frequencies to which they respond.

Question 26

Isointensity curves

Answer 26

Map of plotting the firing rate of an audtiory nerve fiber against varying frequneies at varying intensities

Question 27

What happens to the neuron’s response as the intensity of the sound increases?

Answer 27

Frequencies that had little response at low intensities (20 decibels) now evoke substantial responses as the intensity increases (80 decibels).