Module 2 Class Note Questions

Question 1

What is sound?

Answer 1

an energy wave of molecules (or pressure wave) that creates a vibration

Question 2

What causes sound?

Answer 2

vibrations sets particles in the surrounding medium (typical air) in vibrational motion, thus transporting energy through the medium
-cycles per second

Question 3

What aspect of the physical energy of sound changes when the sound gets louder or higher pitched?

Answer 3

The physical energy (amplitude) increases as a signal becomes louder
-ex: quietest sound possible= 0 db
-shorter wavelength= higher frequency
The energy is more on a loud signal and less on a quiet signal
References to the existence of the Doppler effect
(ex: ambulance getting high pitched when the energy of the sound wave is pushed when closer)

Question 4

What is the difference between sine waves and complex sounds?

Answer 4

Sine waves consist of single frequency (single wave) while Complex sounds have multiple frequencies present (combo of waves)

Question 5

What is a Pinna?

Answer 5

the outer part of the ear that sticks out; the curly structure on the side of the head that we typically call an ear
-the ridges in the ear help detect and localize sounds

Question 6

How is sound funneled into the ear?

Answer 6

-The Pinna funnels sound waves into and through the ear canal

Question 7

What is the Tympanic membrane?

Answer 7

a thin sheet of skin that moves in and out in response to the pressure changes of sound waves
-eardrum; the border between the outer and middle ears

Question 8

What is the function of the ossicles?

Answer 8

To amplify sound waves and transmit the vibrations from the tympanic membrane to the oval window

Question 9

How do the Ossicles amplify the sound?

Answer 9

They amplify sound by two ways:
1-Joints are hinged so they work like levers: a modest amount of energy on one side of the fulcrum (joint) becomes larger on the other
-increases the amount of pressure change by a third
2-Energy is concentrated from a large surface (tympanic membrane) to a small surface (oval window)
-pressure on the oval window is magnified 18x relative to the pressure on the tympanic membrane

Question 10

What is the Cochlea?

Answer 10

‘hearing’ part of the inner ear; a tiny coiled structure embedded in the temporal bone of the skull
-interacts with the middle ear via two membranes, used to relieve pressure
-oval window
(ex: end being pushed on)
-round window
(ex: other side that relieves the pressure)
-filled with watery fluids in 3 parallel canals
-Vestibular canal: bigger and pushes on the middle canal
-Middle canal
-Tympanic canal
-closed system, the change in pressure causes
-ex: balloon- push on one end, pressure will vibrate back on the other end

Question 11

What is the function of hair cells?

Answer 11

any cell that stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some also receive inputs from the brain
-The hair cells are responsible for supporting specialized neurons and provide a foundation for stereocili

Question 12

What is the Organ of Corti?

Answer 12

a structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers

Question 13

What is the Tectorial membrane?

Answer 13

=a gelatinous flap that is attached at one end and rests atop of hair cells on the other
-As the basilar membrane moves it causes the hair cells to shear against the tectorial membrane in the opposite direction

Question 14

How is the movement in the cochlear partition translated into neural signals?

Answer 14

Through a series of steps involving the hair cells located in the organ of Corti

Question 15

How is the amplitude coded in the cochlea?

Answer 15

-If the amplitude of the sound wave is increased, the tympanic membrane and oval window move farther in & out with each pressure fluctuation
=>making the bulge in the vestibular canal bigger, causing the cochlear partition to move farther up & down, causing the tectorial membrane to shear across the organ of Corti more forcefully, which causes the hair cells to pivot farther back & forth, which causes more neurotransmitters to be released, which causes auditory nerve fibers to initiate action potentials more quickly

Question 16

How is frequency coded in the cochlea?

Answer 16

-Cochlear place code= different portions of the cochlea are tuned to different frequencies
-different spots that move up and down more
-closer to oval window is high pitch/frequency, closer to the other window is low pitch/frequency

Question 17

What is the function of the auditory nerve?

Answer 17

-Auditory nerve fibers synapse with each inner hair cell, these are afferent fibers (send information to the brain)
-Auditory nerve can only fire so much, louder sound= faster firing rate
-Join the vestibular nerve fibers to make up cranial nerve VIII or the vestibulocochlear nerve
-All auditory nerve fibers synapse in the cochlear nucleus
-Different fibers selectively respond to different sound frequencies

Question 18

Are individual nerve fibers selective for different sound frequencies?

Answer 18

Yes

Question 19

What is phase locking?

Answer 19

many fibers will fire action potentials at one particular point of the sound wave; a neuron fires with the specific phase of the stimulus/response
-Limited by sound frequency, reliable for low frequencies
-Higher frequencies would need multiple nerve fibers for neurons to encode (Volley principle)
-May occur because Auditory nerve fibers fire when the stereocilia of hair cells move in one direction but do not fire when the stereocilia move in the other direction
-The existance of phase locking means that the firing pattern of an Auditory Nerve (AN) fiber carries a temporal code for the sound wave frequency

Question 20

How does auditory nerve encode sound frequency?

Answer 20

Temporal code for Frequency
= tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of the sound
-Volley principle= multiple neurons encode frequency as a group

Question 21

What is the auditory pathway in the brain? (ECO-LIMA)

Answer 21

E- Ear (outer ear, middle ear, inner ear)
C- Cochlear nucleus
O -Superior Olive
L- Lateral lemniscus
I- Inferior Colliculus
M -Medial Geniculate Nucleus
A- Auditory cortex

Question 22

At what point does information from both ears become integrated?

Answer 22

Superior olives is an early brainstem region in the auditory pathway where inputs from both ears converge

Question 23

What is the function of the medial geniculate nucleus?

Answer 23

-Part of the thalamus that relays auditory signals to the cortex

Question 24

What is tonotopic organization?

Answer 24

the classification of different levels of frequency; the tones are topically organized
-Tonotopic organization is loosely maintained in the Primary Auditory Cortex region

Question 25

Rate Saturation

Answer 25

= as the sound gets louder, auditory nerve fibers become more broadly tuned
-To circumvent rate saturation, the auditory system uses auditory nerve fibers with different spontaneous rates
-High spontaneous rate fibers respond at low levels of sound
-Low spontaneous rate fibers respond at a broader range of intensities but not at low intensities

Question 26

What is the function of the auditory cortex?

Answer 26

Processing of tones; ensuring Tonotopic organization