lecture 12

Question 1

what determines the sound of a stimulus

Answer 1

frequency with pressure change

compression wave generated by vibrating air molecules

Question 2

complex waves

Answer 2

the sum of multiple sine waves

Question 3

what is the audible human spectrum

Answer 3

20hZ-20kHz or 15 when older

Question 4

external and middle ear purpose

Answer 4

collect sound waves and amplify pressure to transfer energy to fluid filled cochlea of inner ear
contributes to localization of sound in space

Question 5

external ear parts

Answer 5

pinna, concha and auditory meatus

Question 6

middle ear parts

Answer 6

malleus/incus/stapes, tympanic membrane (ear drums), cochlea
lever action of inner ear bones provides mechanical advantage to increase pressure on stapes

Question 7

tensor tympani and stapedius

Answer 7

small muscles that regulate efficiency of transmission of sounds to inner ear
control the tension on the bone

Question 8

crickets

Answer 8

don’t have peripheral system to block out their own song so they must have central circuits to gate out input from own singing

Question 9

presbycusis

Answer 9

high frequency hearing loss with age

Question 10

2 nerves innervating cochlea

Answer 10

vestibular- tells you about motion/ position

auditory- tells you about sound

Question 11

cochlea ear chambers

Answer 11

scala tympani
scala vestiboli
scala media - where tips of hair cells sit

Question 12

inner hair cells

Answer 12

convey sound information to central nervous system

tectorial membrane sits on top of hair cells and moves with incoming wave and depolarizes cells

Question 13

mechanical tuning of basilar membrane

Answer 13

properties of membrane vary across its length- stiffer and floppier at different ends
frequency of wave matches that of membrane
skinner and high frequency (short and stiff) closest to cochlea and lower frequency (floppier) at apex
hair cells encode frequency based on position of basilar membrane

Question 14

tonotopy

Answer 14

topographical mapping of frequency in cochlea maintained in brainstem, thalamus and cortex resulting from physical properties of basilar membrane

Question 15

hearing loss

Answer 15

• cochlear implants
  electrode stimulate secondary afferent axons directly
• brainstem implants
  put an array of electrodes into nucleus and stimulate neutrons of brainstem that are tonotopically arranged

Question 16

change in hair cell membrane potential

Answer 16

amount of deflection needed for a detectable voltage is around 100nm for a few mV
deflecting hair bundles causes a change in membrane potential

Question 17

how are movements of the cochlea converted to neural activity in the brain

Answer 17

cochlear movement causes voltage changes in hair cells by sound induction vibration of tectorial membrane opening hair cells and depolarizaing

Question 18

inward current of K

Answer 18

possible because cilia sit in a high K solution so reversal potential is closer to zero
when channels pulled open there is an influx of K which depolarizes and opens co- localized Ca channels

Question 19

K concentrations in cochlea

Answer 19

perilymph- low K, 0mV
inner hair cells- -45mV
endolymph- high K, 80mV
maintained by stria vascularis

Question 20

efferent and affronts of OHC/IHC

Answer 20

inner: efferent modulation is presynaptic to afferent terminal
OHC: efferent controls the synaptic output of hair cell directly

Question 21

secondary sensory cells

Answer 21

receive excitation from hair cells and transmit AP to CNS

“best freuquency” is frequency at which quietest sound will produce a measurable change in firing

Question 22

brainstem neutrons to hair cells

Answer 22

IHC- synapse onto 10-20 afferants
OHC- synapse onto 1 or 2
purpose is to say something has moved in general sound range

Question 23

outer hair cells

Answer 23

deflection opens MET channel to depolarize cell and shorten OHC
tip embedded in base of typamium and amplifies acoustics
loss of OHC - loss of sensitivity to sound and high frequencies

Question 24

motor protein of OHC

Answer 24

prestin

Question 25

auditory pathway

Answer 25

projects to thalamus contra and ipsi after crossing over in the brainstem the mid pons information from 1 ear is relayed to both sides synapses in inferior colliculus - medial geniculate complex of thalamus

Question 26

inf collic and sup oliv.

Answer 26

inferior colliculus - first place auditory information interacts with motor system processes sounds with complex temporal patterns superior olivary complex- first place where information from both ears interact and spatial locations

Question 27

MSO

Answer 27

synaptic potentials from the left and right ears summate to bring MSO cells to threshold and locate sound local lateral inhibition increases sensitivity to time (for frequencies less than 3KHz)

Question 28

LSO

Answer 28

lateral superior olive: intensity differences resulting from sound shadowing by hand frequencies >2-3KHz can use relative intensity to locate sound

Question 29

mauthner cells in fish

Answer 29

crossed inhibition- side activated first blocks activation of other side pressure wave comes in from one side and synapses onto motor neurons that generate contractions to turn away from stimulus uses electrical synapse because need fast transmission

Question 30

vestibular hair cells

Answer 30

low frequency sensitive- increased Ca causes slipping of myosin decreased Ca causes tension in myosin - peripheral adaptation redefines the dynamic range