Chapter 40: Problem 5

How does the structure of the inner ear allow for the perception of pitch? Of loudness?

Short Answer

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The inner ear allows for the perception of pitch and loudness through the intricate interplay of its components: the cochlea, basilar membrane, hair cells, and auditory nerve. Sound vibrations entering the cochlea cause fluid movement, leading to the vibration of the basilar membrane. The pitch of a sound is determined by the specific section of the basilar membrane that vibrates most, due to its varying stiffness. Hair cells on the basilar membrane detect these vibrations and create electrical signals representing loudness, which are then transmitted to the brain by the auditory nerve, allowing us to perceive both pitch and loudness.

Step by step solution

Understand the Components of the Inner Ear

We need to know the main parts of the inner ear that play a role in the perception of pitch and loudness. These parts include the cochlea, which is a spiral-shaped, fluid-filled structure, the basilar membrane, which is inside the cochlea, hair cells that are sensory receptors located on the basilar membrane, and the auditory nerve that transmits signals from the hair cells to the brain.

Know the Role of the Cochlea

The cochlea is the main structure in the inner ear responsible for transforming sound vibrations into nerve impulses. It is filled with fluid that moves in response to sound vibrations entering the inner ear. This fluid movement causes the basilar membrane to vibrate, which in turn affects the hair cells on its surface.

Understand the Role of the Basilar Membrane

The basilar membrane is a crucial component in the perception of pitch. Its stiffness varies along its length, being stiffer at the base near the entrance of the cochlea and more flexible at the apex farthest from the entrance. This variation in stiffness means that different sections of the basilar membrane resonate in response to different frequencies. Higher frequencies produce maximal displacement near the base, whereas lower frequencies produce maximal displacement near the apex.

Learn about Hair Cells and Auditory Nerve

Hair cells are sensory receptors that play a key role in the perception of loudness. When the basilar membrane vibrates, the movement of hair cell stereocilia creates an electrical signal. This electrical signal is then transmitted to the brain by the auditory nerve. Louder sounds cause larger movements of the basilar membrane and, consequently, a stronger electrical signal in the hair cells. This stronger electrical signal is interpreted by the brain as a louder sound.

Putting It All Together

When sound vibrations enter the inner ear, they cause the fluid inside the cochlea to move, leading to the vibration of the basilar membrane. The pitch of a sound is determined by which part of the basilar membrane vibrates most due to the variation in stiffness along the membrane's length. Hair cells on the basilar membrane detect these vibrations and create electrical signals that represent the loudness of the sound. The auditory nerve then transmits these signals to the brain, where they are perceived as pitch and loudness.

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How does the structure of the inner ear allow for the perception of pitch? Of loudness?

Short Answer

Step by step solution

Understand the Components of the Inner Ear

Know the Role of the Cochlea

Understand the Role of the Basilar Membrane

Learn about Hair Cells and Auditory Nerve

Putting It All Together

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