Auditory System (Hearing)Sound Properties:Propagates through gases, liquids, and solids (metals);Cycle: successive compression and rarefaction of medium;Frequency (pitch): cycles per seconds = Hertz (Hz – humans: 20-20,000 Hz);Intensity (loudness): logarithmic scale (decibels – dB); very sensitive & wide range (0 – 160+ dB);Complexity (timber): additivity ofsimple waves gives rise to complexwaves (most sounds are complex);The Human Ear and Sound PropagationSound wave processing:Sound wavesTympanic membraneOssiclesOval windowCochlear fluidHair cells “transducers”Sensory neurons responseMiddle Ear MechanismsSound Amplification by the OssiclesThe Attenuation ReflexOnset of loud sound causes tensor tympani and stapedius muscle contractionFunction: Adapt ear to loud sounds, improves speech perceptionCross Section of The CochleaPerilymph: Fluid in scala vestibuli and scala tympaniEndolymph: Fluid in scala mediaEndocochlear potential: Endolymph electric potential 80 mV more positive than perilymphInner Ear:The CochleaUncoiling the pea size cochlea;Perilymph is continuous between scala vestibuli and tympaniMovement of stapes imparts movement to basilar membraneThe Hearing Structure Within the Cochlea:The Organ of CortiOuter and inner hair cells embedded in Deiter’s cells and Rods of Corti, within the Organ of Corti;stereocilia contained at the top of each hair cell, extending partially into tectorial membrane;Inner hair cells are mostly responsible for providing auditory information eventually reaching the brain (outer hair cells regulate “tightness” of the cochlea)Transduction of Sound Pressure by Hair CellsSound pressure → perilymph/endolymph movement → basilar membrane movement → hair cell stereocilia movement against tectorial membrane;stereocilia movement ↑or↓ polarization of hair cells via tip link regulation of TRPA1 channels → ↑or↓ of voltage-gated calcium channels → ↑or↓ of neurotransmitter release onto terminals of spiral ganglion neurites.StereociliaApproximately 100 at the top of each hair cell;Movement toward long stereocilia = depolarization;Movement toward short stereocilia = hyperpolarization;Short to long stereocilia connected via tip link filaments.Coding Of Sound Intensity (Loudness)Determined by both firing frequency, and number, of spiral ganglion neurons (related to hair cell activity on basilar membrane);ex. soft sound = fewer AP, loud sound = more AP, from spiral bipolar neurons.Coding Of Sound Frequency1. Place coding:a. Different frequencies vibrate basilar membrane at different spots/places;b. Works for moderate to high frequencies - 200 to 20,000 Hz;- near base: high frequencies (20,000 Hz);- near apex: lower frequencies (200 Hz)2. Phase-lock coding (also called rate coding):a. Frequency of sound = frequency of action potentials locked on specific wave phase;b. Multiple phase-locked fibers together (volleys);c. Works for low to medium frequency sounds (~ 20-4000 Hz)Coding Of Sound Localization: Horizontal Plane1. Interaural time delay: Time taken for sound to reach from ear to ear;2. Interaural intensity difference: Intensity differences between the two ears;3. Duplex theory of sound localization (both mechanisms employed):Interaural time delay: 20-2000 HzInteraural intensity difference: 2000-20000 HzCoding Of Sound Localization: Vertical PlanePrecise shape of pinna provides slightly different echo times to sounds coming from different vertical angles.Frequency (tonotopic) organization maintained throughout auditory system all the way to primary auditory cortexPrimary auditory cortex = posterior superior temporal gyrusNRSC 2100 1st Edition Lecture 15Auditory System (Hearing)• Sound Properties:– Propagates through gases, liquids, and solids (metals);– Cycle: successive compression and rarefaction of medium;– Frequency (pitch): cycles per seconds = Hertz (Hz – humans: 20-20,000 Hz);– Intensity (loudness): logarithmic scale (decibels – dB);very sensitive & wide range (0 – 160+ dB);– Complexity (timber): additivity of simple waves gives rise to complex waves (most sounds are complex);The Human Ear and Sound PropagationSound wave processing:• Sound waves• Tympanic membrane• Ossicles• Oval window• Cochlear fluid• Hair cells “transducers”• Sensory neurons responseMiddle Ear MechanismsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Sound Amplification by the Ossicles• The Attenuation Reflex– Onset of loud sound causes tensor tympani and stapedius muscle contraction– Function: Adapt ear to loud sounds, improves speech perceptionCross Section of The Cochlea• Perilymph: Fluid in scala vestibuli and scala tympani• Endolymph: Fluid in scala media• Endocochlear potential: Endolymph electric potential 80 mV more positive than perilymphInner Ear: The Cochlea• Uncoiling the pea size cochlea;• Perilymph is continuous between scala vestibuli and tympani• Movement of stapes imparts movement to basilar membraneThe Hearing Structure Within the Cochlea:The Organ of Corti• Outer and inner hair cells embedded in Deiter’s cells andRods of Corti, within the Organ of Corti;• stereocilia contained at the top of each hair cell, extending partially into tectorial membrane;• Inner hair cells are mostly responsible for providing auditory information eventually reaching the brain (outer hair cells regulate “tightness” of the cochlea)Transduction of Sound Pressure by Hair Cells• Sound pressure → perilymph/endolymph movement → basilar membrane movement → hair cell stereocilia movement against tectorial membrane;• stereocilia movement ↑or↓ polarization of hair cells viatip link regulation of TRPA1 channels → ↑or↓ of voltage-gated calcium channels → ↑or↓ of neurotransmitter release onto terminals of spiral ganglion neurites.Stereocilia• Approximately 100 at the top of each hair cell;• Movement toward long stereocilia = depolarization;• Movement toward short stereocilia = hyperpolarization;• Short to long stereocilia connected via tip link filaments.Coding Of Sound Intensity (Loudness)Determined by both firing frequency, and number, of spiral ganglion neurons (related to hair cell activity on basilar membrane);ex. soft sound = fewer AP, loud sound = more AP, from spiral bipolar neurons.Coding Of Sound Frequency1. Place coding:a.