Passage
Sound waves propagate through many conducting structures in the ear before they are transduced into neuronal signals. When sound waves reach the fluid-filled cochlea, they are detected by hair cells lining the basilar membrane. The cochlear spiral can be modeled as a resonator system because each section of the basilar membrane is sensitive to a specific frequency (Figure 1) .
Figure 1 Amplitude pattern of the basilar membrane for different frequenciesPresbycusis (age-related hearing loss) results from a combination of factors that lessens an individual's mechanical and/or neurological sensitivity to sound. Pure tone audiometry (PTA) is used to determine an individual's ability to detect different sound frequencies and can be used to evaluate presbycusis. A "pure" tone is characterized by a single sinusoidal waveform. An audiogram plots the relative intensity required of a given frequency to be detected by the individual (Figure 2) .
Figure 2 Audiogram of an elderly patient exhibiting presbycusis
-When sound passes from air to the tympanic membrane, what changes occur to the sound's intensity and velocity?

Question

Passage
Sound waves propagate through many conducting structures in the ear before they are transduced into neuronal signals. When sound waves reach the fluid-filled cochlea, they are detected by hair cells lining the basilar membrane. The cochlear spiral can be modeled as a resonator system because each section of the basilar membrane is sensitive to a specific frequency (Figure 1) .

Figure 1 Amplitude pattern of the basilar membrane for different frequenciesPresbycusis (age-related hearing loss) results from a combination of factors that lessens an individual's mechanical and/or neurological sensitivity to sound. Pure tone audiometry (PTA) is used to determine an individual's ability to detect different sound frequencies and can be used to evaluate presbycusis. A "pure" tone is characterized by a single sinusoidal waveform. An audiogram plots the relative intensity required of a given frequency to be detected by the individual (Figure 2) .

Figure 2 Audiogram of an elderly patient exhibiting presbycusis
-When sound passes from air to the tympanic membrane, what changes occur to the sound's intensity and velocity?

Quizplus · Accepted Answer

11ecba2d_12ed_c60b_a3bf_8520b7a44186_MD0008_00 A sound wave carries energy in the form of longitudinal mechanical waves, and the energy is related to the intensity of the sound wave. When sound crosses from one medium to another, a portion of the wave's energy is reflected. Therefore, sound waves lose energy (are attenuated) and their intensity decreases when passing from air to a solid structure, such as the tympanic membrane (Choices A and C). Wave velocity v is the product of wavelength λ and frequency f: v = λf When a wave moves from one medium to another, its frequency does not change. Changes in wave velocity are only due to changes in wavelength. The propagation velocity of sound waves depends on the properties of the medium: Velocity increases with temperature. Velocity is slowest in gases, faster in liquids, and fastest in solids. Within a phase of matter, velocity increases with stiffness and decreases with density. Therefore, when sound passes from air to a solid (such as the tympanic membrane), its propagation velocity increases (Choice B). Educational objective: When sound moves from one medium to another, a portion of its energy is reflected, decreasing its intensity. The propagation velocity of sound depends on the medium and is slowest in gases, faster in liquids, and fastest in solids.

Passage Sound Waves Propagate Through Many Conducting Structures in the Ear