Week 4 Auditory Objective 2

Question 1

Cochlea: what it is and major components

Answer 1

1. consists of three side by side tubes
2. Major components include
   a. Scala vestibuli
   b. Scala media
   c. Scala tympani
   d. Reissners membrane
   (a-c are the major tubes)

Question 2

Reissner’s membrane

a. other name
2. what it separates
3. qualities and outcomes

Answer 2

a. vestibular membrane
b. separates scala vestibuli from scala media
c. because of thinness, media and vestibuli are considered a single chamber
d. Media contains special fluid

Question 3

Basilar membrane

Answer 3

separates scala media from scala tympani
contain 20-30K fibers

distal ends of the fibers are not “fixed” but are embedded in the membrane

fibers vibrate

length increases from oval window to apex of cochlea

fibers diameter decreases in size from oval window

Question 4

What is the result of the basilar membrane/fiber design?

Answer 4

fiber length increases from oval window to apex of cochlea

fibers decrease in diameter from oval window to apex of cochlea

result

1. short stiff fibers beat at a high frequency near oval window
2. long, limber hairs near the apex beat at a low frequency
3. high frequency resonance of basilar membrane occurs near the base
4. low frequency resonance of the basilar membrane occurs near the apex (helicotrema)

Question 5

Organ of Corti

Answer 5

transmit nerve impulse in response to vibrations from basilar membrane

Question 6

Sensory receptors of organ of corti

Answer 6

single row of internal hair cells, 3500; 12 micrometers in diameter

3-4 rows of external hair cells

Question 7

Hair cells stimulate nerve fibers that lead to what kind of ganglion?

Answer 7

spiral ganglion of corti

Question 8

what “kinds” of cilia from hair cells touch/embedded in overlying tectorial membrane?

Answer 8

stereocilia

Question 9

what is the role of bending in the stereocilia embedded in or touching the overlying tectorial membrane

Answer 9

bending polarizes/depolarizes them in opposite directions

Question 10

“outer ends” of hair cells are tightly attach to ______________ and supported by ___________ which are attached to ____________. This arrangement creates a rigid unit

Answer 10

1. reticular lamina
2. rods of Corti
3. basilar fibers

Question 11

what are rods of Corti attached to?

Answer 11

basilar fibers and something else, unidentified yet

Question 12

neurons in spiral ganglion send axons from a specific nerve: what is the nerve and where does it go?

Answer 12

1. CN VIII

2. upper level of the medulla

Question 13

movement of basilar fibers cause movement where?

Answer 13

reticular lamina

Question 14

Movement of the reticular lamina is important because it causes

Answer 14

shearing forces on the hair cells against the tectorial membrane

Question 15

whenever basilar membrane moves, ____ cells

Answer 15

hair cells become excited

Question 16

The apical boarder of a hair cell contains _____ # of stereocilia

Answer 16

100

Question 17

The length of stereocilia become shorter or longer the further away from the modiolus you go?

Answer 17

longer

Question 18

When cilia are bent in the direction of longer ones, a _____ force is created on the _____ cilia

Answer 18

tensile, shorter

Question 19

in the mechanical transduction causes by tensile force produced in bending cilia toward longer cilia a certain kind of channel is opened

Answer 19

200-300 potassium channels, resulting in depolarization of the hair cell membrane

Question 20

scala media is filled with _______

the scala vestibuli is filled with _____

the scala tympani is filled with ______

Answer 20

media = endolymph 
vestibuli = perilymph 
tympani = perilymph

Question 21

Endolymph contains a high concentration of

Answer 21

potassium and low concentration of sodium

perilymph contains high high sodium and low potassium

Question 22

what is the charge differential between endolymph and perilymph?

Answer 22

+80mV = endochoclear potential

Question 23

Hairs that project through the reticular lamina are bathed in

Answer 23

endolymph

Question 24

lower bodies of hair cells are surrounded by

Answer 24

perilymph

Question 25

intracellular potential of hair cells =

Answer 25

• 70mV with respect to perilymph

- 150 mv with respect to endolymph

Question 26

Place Principle

Answer 26

nervous system detects sound frequencies by determining positions along the basilar membrane that are most stimulated

Question 27

How does the auditory system determine distinguish sounds from low, low, low sound frequencies

Answer 27

the auditory system detects sound frequencies by determining the position along the basilar membrane that is stimulated, this is a reiteration of the place principle

Question 28

Frequency Principle

Answer 28

from 20-2000 cycles per second, these can cause volleys of nerve impulses synchronized at the same frequencies.

these volleys are transmitted by the cochlear nerve into the cochlear nuclei of the brain

Question 29

Determination of Loudness: 3 methods

Answer 29

1. As sound increases, amplitude causes basilar membrane and hair cells to vibrate more, and the hair cells stimulate the nerve endings more rapidly
2. as amplitude of basilar membrane and hair cells increase, spatial summation of excited hairs from the fringes of the basilar membrane increases (i.e. more nerve fibers rather than through only a few)
3. the outer cells do not become stimulated until vibration reaches significant levels, which apprises the nervous system the sound is loud

Question 30

decibel =

Answer 30

1 deci = increase in sound energy by 1.26 time

1 bel = 10 fold increase

1 decibel = .1 bel

Question 31

young people can hear sound frequencies between

Answer 31

20 and 20,000 cycles per second

old age its 50 to 8000 cycles