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After completing this unit, you should be able to: Describe the structure and general function of the outer, middle, and internal ears; describe the sound conduction pathway to the fluids of the internal ear, and follow the auditory pathway from the spiral organ (of Corti) to the temporal cortex; explain how one is able to differentiate pitch and loudness, and localize the source of sounds;. | 15 The Special Senses: Part D Properties of Sound Sound is A pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object A sound wave Moves outward in all directions Is illustrated as an S-shaped curve or sine wave Figure 15.29 Area of high pressure (compressed molecules) Crest Trough Distance Amplitude Area of low pressure (rarefaction) A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. (b) Sound waves radiate outward in all directions. Wavelength Air pressure Properties of Sound Waves Frequency The number of waves that pass a given point in a given time Wavelength The distance between two consecutive crests Amplitude The height of the crests Properties of Sound Pitch Perception of different frequencies Normal range is from 20–20,000 Hz The higher the frequency, the higher the pitch Loudness Subjective interpretation of sound intensity Normal range is 0–120 decibels (dB) Figure 15.30 Time (s) (a) Frequency is perceived as pitch. High frequency (short wavelength) = high pitch Low frequency (long wavelength) = low pitch (b) Amplitude (size or intensity) is perceived as loudness. High amplitude = loud Low amplitude = soft Time (s) Pressure Pressure Transmission of Sound to the Internal Ear Sound waves vibrate the tympanic membrane Ossicles vibrate and amplify the pressure at the oval window Pressure waves move through perilymph of the scala vestibuli Transmission of Sound to the Internal Ear Waves with frequencies below the threshold of hearing travel through the helicotrema and scali tympani to the round window Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane at a specific location, according to the frequency of the sound Figure 15.31a Scala tympani Cochlear duct Basilar membrane 1 Sound waves vibrate the tympanic membrane. 2 Auditory ossicles vibrate. Pressure is amplified. 3 Pressure waves created by the | 15 The Special Senses: Part D Properties of Sound Sound is A pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object A sound wave Moves outward in all directions Is illustrated as an S-shaped curve or sine wave Figure 15.29 Area of high pressure (compressed molecules) Crest Trough Distance Amplitude Area of low pressure (rarefaction) A struck tuning fork alternately compresses and rarefies the air molecules around it, creating alternate zones of high and low pressure. (b) Sound waves radiate outward in all directions. Wavelength Air pressure Properties of Sound Waves Frequency The number of waves that pass a given point in a given time Wavelength The distance between two consecutive crests Amplitude The height of the crests Properties of Sound Pitch Perception of different frequencies Normal range is from 20–20,000 Hz The higher the frequency, the higher the pitch Loudness Subjective interpretation of sound intensity Normal range is 0–120 .
