Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 11: Auditory System (Sound wave (cycle (distance between…
Chapter 11: Auditory System
Sound wave
Compressed air (increased density)
Rareified air (less dense)
cycle
distance between successive compressed patch
pitch (sound frequency)
number of cycles per second
intensity (loudness) = amplitude
difference in pressure between compressed and rarefied patches of air
phase
location of sine wave relative to some time point
Structure of ear
outer ear
pinna conducts sounds into auditory canal towards tympanic membrane (ear drum)
middle ear
tympanic membrane
ossicles
malleus
incus
stapes
Middle ear amplifies sound
2 impedance matching mechanisms to overcome energy mismatch between air and water
lever-arm ratio
ossicles act as levers
malleus arm is shorter than incus arm
small movements in malleus --> large movements in incus
Area ratio
amplification due to larger area of tympanic membrane compared to the footplate of the stapes in the oval window
pressure = force/area
inner ear
cochlea - fluid-filled (where receptor cells live)
3 chambers (scalae) of cochlea
scala vestibuli
fluid: perilymph
perilymph composition is like extracellular fluid - low K, high Na
scala media
fluid: endolymph
composition like intracellular fluid - high K low Na
stria vascularis pumps K into scala media
scala tympani
fluid: perilymph
sound transduction accomplished in the organ of corti
organ of corti sits on basilar membrane
organ of corti: from fluid motion to changes in Vm
hair cells form synapses on neurons whose cell bodies are in the spiral ganglion
spiral ganglion cells receive synaptic input from hair cells, project to the brain in the VIII
Hair cell
sterocilia looks like hair
2 more items...
mechanically gated channels are connected by elastic filaments called tip links
3 more items...
receptor potential follows stimulating waveform for low frequencies
1 more item...
outer hair cells
2 more items...
inner hair cells
2 more items...
inner ear is the frequency analyzer
cochlea breaks incoming complex sounds into component frequencies
basilar membrane - moves up and down with movement of perilymph
move toward base: narrow/stiff, high frequency
move towards apex: wide/floppy, low frequency
Basic auditory pathway
sound waves move tympanic membrane
tympanic membrane moves ossicles
ossicles move membrane at oval window
motion at oval window moves fluid in cochlea
movement of fluid in cochlea causes response in sensory neurons
Auditory pathways (same for VCN and DCN, but DCN passes superior olive)
afferents from spiral ganglion enter brain stem in auditory nerves --> ventral cochlear nucleus (IPSILATERAL)
project to superior olive on both sides of brain
ascend in the lateral lemniscus
innervate inferior colliculus
send axons to MGN of thalamus
projects to auditory cortex
DCN: frequency analysis
each 8th nerve fiber has a characteristic frequency - that frequency with the lowest threshold intensity
Place code: tonotopy
Phase locking
low frequencies phase lock - consistent firing of a cell at the same phase of a sound wave
intermediate frequencies use volley principle - pooled activity of many neurons codes every cycle, response is phase locked but not on every cycle
high frequencies can't phase lock, only use tonotopy
VCN: sound localization
Horizontal plane: interaural timing differences for low frequencies (wavelength > width of head)
wave diffracts around head with no intensity loss
for continuous sounds
only thing that can be compared is the time at which the same phase of the sound wave reaches each ear
Binaural neurons in medial superior olive are tuned to different intramural time delays, EE cells
delay lines and coincidence detectors
Horizontal plane: interaural intensity differences for high frequencies (wavelength < width of head, sounds>2000Hz)
sound reflects off head, creating sound shadow
sound is less intense in ear with sound shadow
binaural neurons in lateral superior olive are tuned to different interaural intensity differences, EI cells
Ipsilateral ear provides excitatory input to LSO cell
contralateral ear provides inhibitory input to LSO cell
pinna is important for sound localization in vertical plane
detection of sound in vertical plane requires only one ear
sound reaches auditory canal by both direct and reflected pathways
brain localizes source of sound by detecting differences in combined sounds from direct and reflected pathways
Auditory system encodes Intensity
increase intensity by
increasing firing rate
increase number of active neurons
auditory cortex
columnar organization
isofrequency bands: sound frequency
binaural bands: sound location