auditory function and balance Flashcards
central auditory pathways: list the main structures in the central auditory pathways and their functions, explain tonotopic mapping, and identify the part of the pathway involved in auditory reflexes
two types of hair cell and relative abundance
inner hair cell (less abundant), 3 rows of outer hair cell (30x more abundant)
where do most afferent projections (signal from cochlea to brain) project from and function
inner hair cells (provide sensory tranduction)
where do most efferent projections (signal from brain to cochlea) connect to and function
outer hair cells (provide energy to mechanically amplify low-level sound entering cochlea)
diagram of inner and outer hair cells in Organ of Corti
source of energy for active processes by which cochlea has sensitivity and sharp frequency selectivity
electromotility
how does electromotility produce energy
body of outer hair cells shortens and elongates when internal voltage is changed, due to the reorientation of the protein prestin
where do hair cells form synapses with sensory neurones
in cochlear (spiral) ganglion
what does each ganglion cell do
responds best to resonant frequency of basilar membrane in same area, forming tonotopic map
define tonotopic map
sound-location map where low frequencies are ventral and high frequencies are dorsal (spatial organisation of response to frequency is preserved throughout pathway)
where is tonotopic mapping present
cochlear nucleus
what conveys information to cochlear nucleus
nerve fibres
diagram of ear to primary auditory cortex
what does the dorsal cochlear nucleus do and how
locates sound in vertical plane due to high frequencies producing intensity differences between the two ears
what are spectral cues and how are they produced in dorsal cochlear nucleus to locate direction of sound
high-frequency sounds produce interference within body; ears detect and affect differently sounds coming from different directions due to asymmetrical shape (spectral cues)
what does the superior olivary complex do
compares bilateral activity of cochlear nuclei (from both ears)
where is the medial superior olive
pons (medially)
what happens in the medial superior olive, and how it does this
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)
where is the lateral superior olive
pons (laterally)
what happens in the lateral superior olive
detects differences in intensity between the two ears (interaural level difference is computed to localise sounds in the horizontal plane)
lateral superior olive: side of excitation
ipsilateral
lateral superior olive: side of inhibition
contralateral
lateral superior olive: when must excitation and inhibition arrive
excitation arriving ipsilaterally must arrive at same time as inhibition from contralateral side
lateral superior olive: diagram of excitation and inhibition
lateral superior olive: what is contralateral inhibitory signal carried out via
large axons with large synapses (the large calyces of Held), so faster (reach at same time as excitatory as travel more distance)
lateral superior olive: what is ipsilateral excitatory signal carried out via
smaller axons that conduct more slowly (reach at same time as inhibitory as travel less distance)
where do superior olivary complex neurones send feedback to
hair cells (mainly outer hair cells in cochlea), and forward to central pathways
effect of activity in superior olivary complex neurone fibres
increases representation of signals in noise and protects it from damage by loud sounds
diagram of superior olivary complex neuronal feedback
2 functions of activity of superior olivary complex neurones
balance responses from the two ears; reduce cochlea sensitivity
where do all ascending auditory pathways converge
inferior and superior colliculus in midbrain
3 sections of inferior colliculus
central nucleus, dorsal cortex, external cortex
which section of inferior colliculus is tonotopically orgaised
central nucleus
describe precedence effect in inferior colliculus and its basis
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
what happens in superior colliculus
auditory and visual maps converge; neurones tuned to respond to stimuli with specific sound directions
significance of auditory map created in superior colliculus
fundamental for reflexes in orienting the head and eyes to acoustic stimuli
function of auditory cortex
neurones respond to sound
where is primary auditory cortex A1 located
superior bank of the temporal lobe
mapping in A1
tonotopical mapping (subdivided according to frequency response), as well as loudness, rate and frequency modulation; related to gaze control in response to complex tasks
A1 mapping interactions: training by remodelling A1
can be trained in dyslexia and brain repair
function of superior auditory cortex
identification of sound: dorsal pathway determines where, ventral pathway determines what
where do collateral pathways go
reticular formation and cerebellum
what does lateral inhibition in ascending pathway enhance
resolution of similar frequencies
what do descending pathways provide feedback at
all levels
what happens in secondary cortex
neurones respond to more complex sound patterns
