auditory system

Question 1

hearing and deafness relevance to vet med

Answer 1

patients

• congenital deaf animals
• age related hearing loss

you and your clients

• noise-induced hearing loss (occupational hazard)

humans are exquisite consumers of the auditory system

• protects us against the things we hear
• speech acquisition

Question 2

acoustic waves are in regions of (2)

Answer 2

• higher air pressure - condensations
• lower air pressure - rarefactions

Question 3

how fast does sound travel

Answer 3

344 m/sec in air

Question 4

perception of sound correlates to physical attributes of acoustic stimuli, such as (2)

Answer 4

• pitch
• loudness

Question 5

what is pitch and loudness

Answer 5

• pitch = frequency
• loudness = amplitude

Question 6

perception of pitch

Answer 6

• sinusoidal pressure wave = simple sound
• frequency expressed in cycles per sec or Hertz
• frequency related to subjective expereience of pitch

Question 7

perception of loudness

Answer 7

• sinusoidal pressure waves = simple sound
• peak-to-peak variation in pressure gives impression of loudness

Question 8

how is sound intensity measured

Answer 8

• in decibels (dB SPL) (sound pressure level)
• dB is one-tenth of a Bel
• Bel is one log unit
• 0 dB is ~threshold for humans at 1-4 kHz
• measurement relative to 20 microPascals

Question 9

complex sound

Answer 9

• most frequent acoustic signal - speech
• multiple frequencies occuring simultaneously
• job of inner ear is to decompose complex sound into its primary sine wave components

Question 10

bony parts of labyrinth

Answer 10

• series of channels in bone
• envelops membranous labyrinth

Question 11

membranous part of labyrinth

Answer 11

• soft tissue contain sensory cells for hearing and balance
• dorsal is vestibular (semi-circular canals, utricle, and sacculus)
• ventral is auditory (cochlea)

Question 12

oval window in organ or corti

Answer 12

• stapes footplate inserts here at extreme base of cochlea
• end of scala vestibuli

Question 13

round window in organ of corti

Answer 13

at end of scala tympani

Question 14

what is the cochlea

Answer 14

• coiled structure with snail-like appearance
• 3 chambers

Question 15

what are the 3 chambers of the cochlea

Answer 15

1. scala vestibuli - upper - perilymph
2. scala tympani - lower - perilymph
3. scala media - middle - endolymph

Question 16

scala media components

Answer 16

• houses organ of corti
• apical surface sensory cells bathed in intracellular like ionic environments (high K, low Na)

Question 17

organ of corti

Answer 17

• receptor organ of hearing
• 8 different cell types that rest on basilar membrane

Question 18

hair cells of organ of corti

types

Answer 18

• mechano-sensory cells
• 3 rows of outer hair cells (efferent)
• 1 row of inner hair cells (afferent)

Question 19

hair cells or organ or corti characteristics and communication

Answer 19

• characteristic sensory hairs or stereocilia on apical surface
• communicate with overlying tectorial membrane

Question 20

hair bundles

Answer 20

stereocilia - sensory hairs

• actin rich make them rigid rods
• extracellular links between sensory hairs
• tip links - essential to transduction process
• displacement creates tension on tip links
• opens transduction channels

Question 21

transduction

Answer 21

• deflection toward tallest hairs - depolarization
• deflection away from tallest hairs - hyperpolarization
• asymmetric process excitatory > inhibitory

Question 22

transduction channel

Answer 22

• located near tips of stereocilia
• non-specific cationic channel
• saturates with movements as small as 100 nm

Question 23

auditory nerve

Answer 23

afferent fibers to the brain

• IHCs contacted by ~ 10 auditory nerve fibers
• contact about 3 OHCs
• specialzied synapses to allow high and prolonged rates of synaptic transmission

Question 24

outer hair cells

Answer 24

• both sensory and motor elements
• motile
• contraction and elongation (induced by voltage changes or inhibitory NT release)
• modifies cochlear mechanics
• serves to sharpen cochlear frequency selectivoty
• cochlear amplifier

Question 25

damage to hair cells

Answer 25

• drug insults (aminoglycosides)
• viral infection
• degeneration of genetic origin
• acoustic overstimulation (break tip links or disrupt actin core - ineffective transduction; hair cell death - excito-toxicity)