auditory system Flashcards
hearing and deafness relevance to vet med
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
acoustic waves are in regions of (2)
- higher air pressure - condensations
- lower air pressure - rarefactions
how fast does sound travel
344 m/sec in air
perception of sound correlates to physical attributes of acoustic stimuli, such as (2)
- pitch
- loudness
what is pitch and loudness
- pitch = frequency
- loudness = amplitude
perception of pitch
- sinusoidal pressure wave = simple sound
- frequency expressed in cycles per sec or Hertz
- frequency related to subjective expereience of pitch
perception of loudness
- sinusoidal pressure waves = simple sound
- peak-to-peak variation in pressure gives impression of loudness
how is sound intensity measured
- 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
complex sound
- most frequent acoustic signal - speech
- multiple frequencies occuring simultaneously
- job of inner ear is to decompose complex sound into its primary sine wave components
bony parts of labyrinth
- series of channels in bone
- envelops membranous labyrinth
membranous part of labyrinth
- soft tissue contain sensory cells for hearing and balance
- dorsal is vestibular (semi-circular canals, utricle, and sacculus)
- ventral is auditory (cochlea)
oval window in organ or corti
- stapes footplate inserts here at extreme base of cochlea
- end of scala vestibuli
round window in organ of corti
at end of scala tympani
what is the cochlea
- coiled structure with snail-like appearance
- 3 chambers
what are the 3 chambers of the cochlea
- scala vestibuli - upper - perilymph
- scala tympani - lower - perilymph
- scala media - middle - endolymph
scala media components
- houses organ of corti
- apical surface sensory cells bathed in intracellular like ionic environments (high K, low Na)
organ of corti
- receptor organ of hearing
- 8 different cell types that rest on basilar membrane
hair cells of organ of corti
types
- mechano-sensory cells
- 3 rows of outer hair cells (efferent)
- 1 row of inner hair cells (afferent)
hair cells or organ or corti characteristics and communication
- characteristic sensory hairs or stereocilia on apical surface
- communicate with overlying tectorial membrane
hair bundles
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
transduction
- deflection toward tallest hairs - depolarization
- deflection away from tallest hairs - hyperpolarization
- asymmetric process excitatory > inhibitory
transduction channel
- located near tips of stereocilia
- non-specific cationic channel
- saturates with movements as small as 100 nm
auditory nerve
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
outer hair cells
- 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
damage to hair cells
- 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)
