THE AUDITORY SYSTEM AND HEARING

The perceptual dimension that corresponds to the physical dimension of sound intensity (or amplitude) is ________

loudness

higher sound intensity produces ______ axons firing simultaneously in the auditory nerve

more

Sitting on the basilar membrane is a structure called the ___________ that contains the auditory receptor cells.

organ of Corti

conduction deafness

ossicles can be damaged by a severe middle ear infection

The _______ hair cells are analogous to the _____ of the visual system; they show high convergence and are important for hearing low intensity sounds.

outer; rods

while the stapes presses against a membrane-covered opening in the bony wall of the cochlea called the__________

oval window

The scala vestibuli and the scala tympani are joined at the ______,

apex

The ___________ shows the auditory threshold as a function of frequency.

audibility curve

Hair cells are unlike typical neurons. Like rods and cones, they lack ________, so they only transmit graded potentials.

axons

The ________ or outer ear focuses the sound waves into the auditory canal, which carries them to the extremely thin membrane called the _________ or tympanic membrane

pinna; eardrum

The perceptual dimension of sound that corresponds to the physical dimension of frequency is ________.

pitch

There is a very good reason to use frequency instead of wavelength to describe the wave aspect of sound: It is because:

pitch perception depends on frequency, not wavelength.

The general rule is that the denser the medium, the _______ the speed of sound.

faster

Like light, sound has a wave aspect; but for sound, unlike light, the wave aspect is usually described in terms of __________ rather than wavelength.

frequency

Thus it makes sense to describe sounds in terms of _________ rather than wavelength, because ___________ is what the auditory system encodes.

frequency; frequency

The higher the intensity of sound, the larger the vibrations of the eardrum and ossicles, which results in larger travelling waves on the basilar membrane inside the cochlea.

Coding of intensity

The receptors are called __________ because they have tiny extensions called cilia that look like hairs under a microscope.

hair cells

The _________ the frequency, the sharper the sonar image

higher

the problem of a lot more energy is needed to move a dense medium such as a fluid than to move a rarefied medium such as air. this problem is called:

impedance matching

Some animals can hear ____________: sounds with frequencies of less than 20 Hz

infrasounds

The ________ hair cells show no convergence and in fact show divergence of output to the ganglion cells.

inner

The bending of hairs opens __________ channels in the cell membrane of the hair cells, which depolarizes (excites) the hair cells due to the influx of positively charged potassium ions.

potassium

The physical stimulus in hearing is sound, which consists of ________________ that travel through some physical medium such as air, water, or even solid rock

pressure waves

Like the relationship between intensity and loudness, the relationship between frequency and pitch shows:

response compression

Thus the auditory system, like the visual system, shows ______________ which enables us to perceive and discriminate a huge range of sound intensities.

response compression

The inward motion of the stapes pushes the fluid through the cochlea until it presses against another membrane-covered opening called the _________ and causes that membrane to bulge outward; this is the compression phase of the sound wave.

round window

So like vision there is a dual system for hearing: one specialized for _______, the other specialized for _____________ of the auditory stimulus.

sensitivity; analysis of details

hearing loss due to damage to the auditory receptors or other neural components

sensorineural deafness

These cilia touch or almost touch another stiff membrane called the _______________ that protrudes into the scala media.

tectorial membrane

- below 500 Hz, only the ________ mechanism (timing code) works - above 4000 Hz, only _____ coding works - from 500 to 4000 Hz, ____ mechanisms are working

telephone; place; both

There are two small muscles in the middle ear: the __________ attached to the malleus, and the __________ attached to the stapes.

tensor tympani; stapedius muscle

Because the range of sound intensities that we experience in our everyday perceptual world is so vast, a logarithmic scale is used to describe sounds in terms of their intensity:

the Decibel (dB) scale.

the three ossicles:

the malleus (hammer), incus (anvil) and stapes (stirrup)

Frequency is simply:

the number of waves (or cycles) per unit time

impedance matching is solved by the:

the ossicles or middle ear bones

The fluid motion causes the flexible basilar membrane to move up and down in a _________, which travels down the basilar membrane from the oval window to the apex - like the way a kink travels down a rope when snapped.

travelling wave

Certain animals such as dogs, cats, bats, and dolphins can hear _________: sounds with frequencies higher than 20,000 Hz

ultrasounds

the speed of sound can _______ substantially from one medium to another

vary

The tensor tympani and the stapedius muscles contracts in response to _____________, which limits the range of movement of the ossicles and thereby reduces the amount of vibration transmitted to the cochlea.

very loud sounds

This variation in speed of sound alters the __________ but does not alter the frequency, nor the pitch.

wavelength

the overall firing pattern in the auditory nerve matches the frequency of the sound up to a frequency of about

4000 Hz

Studies have shown that the place coding mechanism works best for frequencies of around _________

500-20,000 Hz

sensorineural deafness

A more serious cause of deafness is loss of hair cells due to exposure to very intense sounds or to a severe inner ear infection.

The basic unit of frequency is:

Hertz (Hz) (cycles per second).

the Decibel (dB) scale range

0 (absolute threshold) to 140 dB (pain threshold for a brief sound).

In the case of sound waves in air (what we most often hear), at the absolute auditory threshold (the minimum sound intensity that can be perceived), there is a change in air pressure of only ___________

0.00002 dynes per cm2

There are two theories of pitch perception

1. Place theory 2. Telephone theory

The upper limit of this range varies according to 2 factors:

1. age 2. exposure to loud sounds

The ossicles amplify the sound vibrations by two mechanisms:

1. lever principle 2. concentration of force

Cochlea is divided in to three fluid filled chambers:

1. scala vestibuli 2. scala tympani 3. scala media

here is a ____________ of sound intensities going from the absolute auditory threshold to the pain threshold or maximum tolerable intensity.

10-millionfold range

One problem for this theory is that axons cannot in principle fire at rates higher than _______, and in reality almost never fire faster than 500 Hz.

1000 Hz

It shows that we are most sensitive to sounds in the frequency range of:

1000-4000 Hz - the frequencies of human speech.

There are about _________ outer hair cells and ______ inner hair cells.

12,000; 3000

Each cochlea contains at least ______ hair cells, which are distributed along the entire length of the basilar membrane

15,000

So together these 2 factors - lever action and concentration of force onto a small area - serve to amplify the energy of vibration by a factor of about:

2 x 15 = 30 times

The average range of frequencies that humans can perceive is approximately:

20 to 20,000 Hz.

the telephone mechanism works best at

20-400 Hz

By contrast, the loudest sounds that we can hear without pain involves changes in air pressure of about ______________

200 dynes per cm2

he scala media is separated from the other chambers by two membranes: the ___________, which is stiff and inflexible, and the ______________ which is flexible

Reissner's membrane; basilar membrane

This theory basically says that the inner ear works like a telephone. Since the basilar membrane vibrates in synchrony with the sound wave, the firing rates of axons in the auditory nerve therefore match the frequency of the sound - like a telephone, in which the frequencies of electrical signals match the frequencies of a person's voice.

Telephone theory

the perceived pitch of a sound depends on the particular place along the basilar membrane that is most stimulated by the sound.

The place thoery

If groups of axons only fire at the peaks of the sound wave, but different axons fire at different peaks, then the firing rate of the auditory nerve as a whole can exceed 500 Hz even if the firing rate of every individual axon never does.

Volley princible

The vibration pattern of the ____________ also explains why our high frequency hearing is the first to go as a result of aging or exposure to loud sounds.

basilar membrane

In order to stimulate the auditory receptor cells, which are located inside the inner ear or ________, the vibrations of air molecules must be translated into motion of the fluid that fills the cochlea and bathes the receptors.

cochlea

The _________ or inner ear is a bony tube filled with fluid. It is coiled into three turns like a snail's shell.

cochlea

By pushing against the oval window, the stapes transmits sound vibrations to the ___________

cochlear fluid

very high-tech hearing aid for sensorineural deafnes

cochlear implant or "bionic ear"

In the ___________ phase, the density or pressure increases above the resting value; in the ____________ phase, the density or pressure decreases below the resting value.

compression; rarefication

Sound waves consist of cycles of ____________ and ___________ of a substance that travel through that substance

compression; rarefication

They are important for pitch discrimination and can be considered analogous to the_______ of the visual system, which are specialized for discriminating fine details.

cones

The formula for calculating the dB level for a sound of a given intensity is:

dB = 20 log (P/P0)

The malleus picks up sound vibrations from the ________

eardrum

They use these very high frequency ultrasounds for __________________ : they are able to perceive objects in their environment by giving off ultrasonic squeaks and then analyzing the pattern of echoes that result when the sound bounces off nearby objects.

echolocation (sonar)

Whales and elephants use infrasounds to communicate over long distances, since low frequency sounds decay much more with distance than high frequency sounds.

slowly

The middle ear muscles also contract whenever we are ___________.

speaking

The depolarization causes hair cells to release excitatory neurotransmitter at the synapses between the hair cells and the ___________, whose axons make up the auditory part of the auditory nerve carrying auditory signals to the brain

spiral ganglion cells