auditory function and balance

Question 1

two types of hair cell and relative abundance

Answer 1

inner hair cell (less abundant), 3 rows of outer hair cell (30x more abundant)

Question 2

where do most afferent projections (signal from cochlea to brain) project from and function

Answer 2

inner hair cells (provide sensory tranduction)

Question 3

where do most efferent projections (signal from brain to cochlea) connect to and function

Answer 3

outer hair cells (provide energy to mechanically amplify low-level sound entering cochlea)

Question 4

diagram of inner and outer hair cells in Organ of Corti

Answer 4

Question 5

source of energy for active processes by which cochlea has sensitivity and sharp frequency selectivity

Answer 5

electromotility

Question 6

how does electromotility produce energy

Answer 6

body of outer hair cells shortens and elongates when internal voltage is changed, due to the reorientation of the protein prestin

Question 7

where do hair cells form synapses with sensory neurones

Answer 7

in cochlear (spiral) ganglion

Question 8

what does each ganglion cell do

Answer 8

responds best to resonant frequency of basilar membrane in same area, forming tonotopic map

Question 9

define tonotopic map

Answer 9

sound-location map where low frequencies are ventral and high frequencies are dorsal (spatial organisation of response to frequency is preserved throughout pathway)

Question 10

where is tonotopic mapping present

Answer 10

cochlear nucleus

Question 11

what conveys information to cochlear nucleus

Answer 11

nerve fibres

Question 12

diagram of ear to primary auditory cortex

Answer 12

Question 13

what does the dorsal cochlear nucleus do and how

Answer 13

locates sound in vertical plane due to high frequencies producing intensity differences between the two ears

Question 14

what are spectral cues and how are they produced in dorsal cochlear nucleus to locate direction of sound

Answer 14

high-frequency sounds produce interference within body; ears detect and affect differently sounds coming from different directions due to asymmetrical shape (spectral cues)

Question 15

what does the superior olivary complex do

Answer 15

compares bilateral activity of cochlear nuclei (from both ears)

Question 16

where is the medial superior olive

Answer 16

pons (medially)

Question 17

what happens in the medial superior olive, and how it does this

Answer 17

interaural time difference in horizontal plane is computed (sounds are first detected at nearest ear before reaching the other; a map of interaural delay can be formed due to delay lines in medial superior olive)

Question 18

where is the lateral superior olive

Answer 18

pons (laterally)

Question 19

what happens in the lateral superior olive

Answer 19

detects differences in intensity between the two ears (interaural level difference is computed to localise sounds in the horizontal plane)

Question 20

lateral superior olive: side of excitation

Answer 20

ipsilateral

Question 21

lateral superior olive: side of inhibition

Answer 21

contralateral

Question 22

lateral superior olive: when must excitation and inhibition arrive

Answer 22

excitation arriving ipsilaterally must arrive at same time as inhibition from contralateral side

Question 23

lateral superior olive: diagram of excitation and inhibition

Answer 23

Question 24

lateral superior olive: what is contralateral inhibitory signal carried out via

Answer 24

large axons with large synapses (the large calyces of Held), so faster (reach at same time as excitatory as travel more distance)

Question 25

lateral superior olive: what is ipsilateral excitatory signal carried out via

Answer 25

smaller axons that conduct more slowly (reach at same time as inhibitory as travel less distance)

Question 26

where do superior olivary complex neurones send feedback to

Answer 26

hair cells (mainly outer hair cells in cochlea), and forward to central pathways

Question 27

effect of activity in superior olivary complex neurone fibres

Answer 27

increases representation of signals in noise and protects it from damage by loud sounds

Question 28

diagram of superior olivary complex neuronal feedback

Answer 28

Question 29

2 functions of activity of superior olivary complex neurones

Answer 29

balance responses from the two ears; reduce cochlea sensitivity

Question 30

where do all ascending auditory pathways converge

Answer 30

inferior and superior colliculus in midbrain

Question 31

3 sections of inferior colliculus

Answer 31

central nucleus, dorsal cortex, external cortex

Question 32

which section of inferior colliculus is tonotopically orgaised

Answer 32

central nucleus

Question 33

describe precedence effect in inferior colliculus and its basis

Answer 33

brain filters out sounds not necessary to localise sound (where multiple stimuli come in fast, filter out lower intensity than original stimulus between 30-50ms); as ascend towards cortex, more neurons become responsive to complex sounds (in inferior calliculus many carry information about sound location); used for reflexes e.g. startle, head turn

Question 34

what happens in superior colliculus

Answer 34

auditory and visual maps converge; neurones tuned to respond to stimuli with specific sound directions

Question 35

significance of auditory map created in superior colliculus

Answer 35

fundamental for reflexes in orienting the head and eyes to acoustic stimuli

Question 36

function of auditory cortex

Answer 36

neurones respond to sound

Question 37

where is primary auditory cortex A1 located

Answer 37

superior bank of the temporal lobe

Question 38

mapping in A1

Answer 38

tonotopical mapping (subdivided according to frequency response), as well as loudness, rate and frequency modulation; related to gaze control in response to complex tasks

Question 39

A1 mapping interactions: training by remodelling A1

Answer 39

can be trained in dyslexia and brain repair

Question 40

function of superior auditory cortex

Answer 40

identification of sound: dorsal pathway determines where, ventral pathway determines what

Question 41

where do collateral pathways go

Answer 41

reticular formation and cerebellum

Question 42

what does lateral inhibition in ascending pathway enhance

Answer 42

resolution of similar frequencies

Question 43

what do descending pathways provide feedback at

Answer 43

all levels

Question 44

what happens in secondary cortex

Answer 44

neurones respond to more complex sound patterns