Quiz 3

1.67 kHz.

Time base of the auditory system = 1.67 kHz.

absolute refractory period (ARP).

Time period for neural transmitter release is governed by the

1.7 - 4.3 kHz.

Volley of sensory cells allows a upper limit of ~

3ms

We are always listening _ behind

The springy basilar membrane is pushed down, the oval window is pushed out, and constant volume is maintained without motion of fluid through the helicotrema. the deflection of the basilar membrane is a wave that travels from the oval window toward the helicotrema

What happens if we push the oval window in quickly?

A nerve cell goes into a refractory state. It cannot fire again until its charge has been built up by a chemical readjustment inside the cell body

What happens to a nerve cell immediately after firing?

Some impulses make the cell fire while some inhibit or block the firing

What happens when a nerve cell receives impulses from many other nerve cells via its dendrites?

Noise Induced hearing loss - 85dB

What is NIHL

the basilar membrane acts as a filter in which the maximum response to a sinusoidal sound wave moves further to the right as the frequency of the wave is decreased.

What is the underlying mechanism that allows the basilar membrane to excite different hair cells for sufficiently differing frequencies?

Motor Cells

What type of cell are the outer hair cells?

Depends on the extent to which the basilar membrane displacements, due to each of the two components

Whether or not two components that are of similar amplitude and close together in frequency can be discriminated depends on what physical mechanism?

1/ARB (1000) RATE THEORY

fmax =

Basilar Membrane

Creates a lopsided Filter

ERB = (24.7 x (4.37 x (fc/1000) + 1

Equation for Critical Bandwidth and Equivalent Rectangular Bandwidth

Volley Theory

Flipping between neurons firing

The frequency difference between the pure tones at the point at which a listener's perception changes from rough and separate to smooth and separate. ERB = (24.7 x (4.37 x (fc/1000) + 1

How can we measure, or describe the perception of, the "critical bandwidth" of a given tone?

Behaves as if it contains a bank of bandpass filters with continually overlapping center frequencies

How did Harvey Fletcher describe how the auditory system behaves?

Through axons. From the movement of electrically charged ions across the nerve cell membrane They travel along the auditory nerve which comes from the cochlea

How do nerve impulses move through the body?

Determined by the location along the cochlear partition, of the hair cells it innervates. There is a map of frequency along the basilar membrane on account of its graded stiffness properties

How do we measure the Frequency Threshold Curve (FTC) of cochlear nerve fier?

Frequency bandwidth created by the cochlea With an ideal rectangle frequency response curve that passes the same power as the auditory filter.

How do we, in a general sense, define the auditory filter function?

Bigger the diameter the faster it goes. Can be very long to go throughout the body for toes and fingers.

How does the size of the axon affect the nerve impulse?

As Frequency goes up width goes up

How does the width of an auditory filter change with the characteristic frequency of the filter?

D of 2 microns - 10 mps D of 20 microns - 120 mps

How fast do nerve impulses move through the body?

.5 Milliseconds to 1 Millisecond

How long is the typical refractory state?

They are continuous with a complete filter for every audible frequency

How many filters are in the auditory system?

3 connected in 1

Inner hair cells

Higher frequencies are mapped to the base of the basilar membrane and low frequencies are mapped low to the apex of the cochlear coils

Is there a change or difference in the Frequency Threshold Curve (FTC) between lower and higher nerve fibers?

True

Low sounds mask Higher sounds

Synapse

Neuron connections

30 60 120 240 480 960 - center frequency - with 9dB slope

Octave filters

1/ARP * (1000) = Fmax =

Rate Theory Equation

ARP (.6ms)

Sets the time base for the auditory system

As the wave on the basilar membrane travels from left to right, it slowly increases in amplitude, peaks, and then rapidly decreases in amplitude. the wave of this particular frequency can't travel beyond a certain "cutoff point" on the cochlea. As it approaches this place, the wave slows, the amplitude increases, and the power of the wave is absorbed.

Suppose we excite the oval window with a steady sine wave; what happens?

Bandpass filter

The Auditory Spectrum acts as a

Characteristic Frequency

The frequency which neural fibers are most sensitive

decreasing accuracy

The louder it gets the less accurate it is. Increasing intensity =

0.6 ms (aka 600 µs).

• ARP of auditory sensory cells ~=

The organ of corti

A spectrum Analyzer

Basilar Membrane

A tuned Resinator

Stereocilia

Allow ions to flow into the sensory cell.

A wave of high frequency can't mask (or hide) a wave of low frequency, while a wave of low frequency can mask a wave of higher frequency.

As the power of a wave traveling through the cochlea is absorbed, a wave of a given frequency can't travel beyond its given cutoff position on the basilar membrane. What is the result of this process?

There is no exact frequency

At what frequencies do changes in perception occur?

The point at which two peak displacements on the basilar membrane begin to emerge from a single maximum displacement on the membrane.

At what point can two tones be heard as being separate as opposed to fused?

When the frequency difference between tones is less than about 12.5 Hz. When the frequency difference is increased above 15 Hz

For the majority of listeners, when are beats usually heard? At what point do beats generally give way to one of a "fused" tone that sounds "rough?"

Outer cells

Gain control

transmit information to different neurons, muscles, and glands. A long fiber that leaves the cell body. Stimulated and fires by hair cells Coated with a fatty insulation layer of myelin

What are Axon's

to change the action potential that is carried by axons into a chemical message. Fibers from the other nerve cells terminate on the dendrites. Pulses from these other nerves can cause the firing of the nerve cell

What are Synaptic Knobs

Small fibers radiate from a motor neuron. Propagate electrochemical stimulation to the cell body.

What are dendrites,

How we encode musical sounds. Our perception of sound depends on where each component frequency produces vibrations along the basilar membrane. Various frequencies cause maximum vibration at various places along the cochlea, the high frequencies at the basal end near the oval window, and the low frequencies farthest toward the apical end. And different nerves go to different parts of the basilar membrane to pick up the pulses caused by vibrations in different places.

What is the "place theory" of pitch perception?

Base attributes of auditory perception on the neural firing rate as a function of place

What is the "rate theory" of pitch perception?

They add energy to the vibration of the part of the basilar membrane which they are mechanically coupled. Acts as a negative resistance counteracting the engery losses in the process of vibration. Part of an automatic v=gain control that reduces relative vibration in response to intense sound waves

What is the function of the outer hair cells?

1000 dB/oct for HF, 100 dB/oct for

What is the range of cutoff slopes observed across the auditory system?

Nerve pulses aren't fast enough to encode the exact waveform shapes of musical sounds

With regard to hearing sound, what is an inherent problem with the timing or potential speed of nerve impulses?

ARP

___ sets the time base of the auditory system