Auditory System (3)

Question 1

how are sound waves generated and propagated

Answer 1

generated through movement in the environment and propagated through gases, liquids, and solids (metals)

Question 2

what are the physical dimensions of sound waves

Answer 2

frequency (pitch): cycles per second (Hz)
intensity (loudness): logarithmic scale (dB)
complexity: additivity of simple waves=complex waves (why noises sound different)

Question 3

what is the normal hearing range in humans

Answer 3

20-20,000 Hz

Question 4

describe the physical characteristics of the ear

Answer 4

outer ear: pinna and auditory canal
middle ear: tympanic membrane, ossicles (malleus, incus, stapes)
inner ear: oval window (where stapes connects), cochlea, auditory-vestibular nerve

Question 5

what is the attenuation reflex and how does it work

Answer 5

adapts the ear to loud sounds and improves speech perception
onset of loud sound contracts the tensor tympani and stapedius muscles, making it harder for the ossicles to vibrate, dampening the sound

Question 6

how do the different components of the ear lead to basilar membrane vibration

Answer 6

movement of the stapes in the oval window moves the endolymph in the cochlea, moving the hair cells, which vibrates the basilar membrane

Question 7

describe the structure of the organ of corti

Answer 7

basilar membrane is on the bottom, inner and outer hair cells are in the middle, the top is covered with the tectorial membrane

Question 8

how do hair cells transduce/transform sound pressure into electrochemical information

Answer 8

sound pressure causes endolymph movement -> basilar membrane movement -> hair cell movement against tectorial membrane -> depolarization/polarization of hair cells -> opening/closing of voltage gated Ca channels -> increase/decrease of neurotransmitter (glutamate) release onto terminals of spiral ganglion neurites

Question 9

what is the role of inner and outer hair cells

Answer 9

inner: provide auditory information that eventually reaches the brain
outer: regulate tightness of cochlea

Question 10

how is sound intensity coded by the cochlea

Answer 10

intensity is determined by the firing frequency and number of spiral ganglion neurons
(ex. soft sound produces fewer action potentials than a loud sound)

Question 11

describe how frequencies are coded in cochlea

Answer 11

place coding: moderate to high frequencies (200-20000)
-different frequencies vibrate different places on
basilar membrane: near base=high, near apex=low
phase-lock coding: low to medium frequencies (20-4000)
-if sound has lower frequency, there is more space in
between AP so the AP and sound wave will have
corresponding peaks

Question 12

how is sound localized horizontally

Answer 12

interaural time delay: time taken to reach ear to ear (low frequencies)
interaural intensity difference: intensity differences between two ears; slightly different amplitudes because of different AP (high frequencies)

Question 13

how is sound localized vertically

Answer 13

shape of the pinna provides different echo times to sounds coming from different angles so path of sound is echoed at different times depending on the vertical plane it is coming from

Question 14

what is tonotopic organization

Answer 14

frequency organization!
apex of cochlea=lower frequencies
base of cochlea=higher frequencies

Question 15

describe the auditory pathway!!

Answer 15

1. sound waves move the tympanic membrane
2. the tympanic membrane moves the ossicles
3. ossicles move the membrane at the oval window
4. the motion at the oval window moves the cochlea
5. the cochlear movement vibrates the basilar membrane to activate the hair cells
6. axons of the hair cells project to the spiral ganglion cells
7. spiral ganglion cells -> ventral cochlear nucleus -> superior olive (next to ear in brain) -> inferior colliculus (midbrain) -> medial geniculate nucleus (thalamus (where info will cross L to R and R to L)) -> temporal lobe/auditory cortex

Question 16

describe the transduction pathway!! (last step of auditory pathway in more detail)

Answer 16

1. bending of cilia depolarizes or hyperpolarizes
   toward long stereocilia=depolarization
   toward short stereocilia=hyperpolarization
2. spiral ganglia received information from the hair cells
3. cochlear nuclei receive this information from the same side ear
4. superior olive nucleus receives information from L and R cochlear nuclei (sound from both ears comes together)
5. projects to inferior colliculus -> medial geniculate nucleus (thalamus) -> primary auditory cortex (superior temporal gyrus)