2. Regarding hearing... explain how the cochlea distinguishes the pitch of a sound and the loudness of a sound. Include the following key terms: low pitch, high pitch, low frequency, high frequency, amplitude, cochlea, endolymph, basilar membrane.

Answer 1

The cochlea is a vital structure in the inner ear that plays a crucial role in hearing by distinguishing between different pitches and loudness of sound.

Pitch Discrimination

The cochlea distinguishes pitch primarily through its structure and how it reacts to sound frequencies:

1. Basilar Membrane: Inside the cochlea, the basilar membrane runs along its length and varies in width and stiffness. This unique structure causes different parts of the membrane to respond to different sound frequencies.

2. High and Low Frequencies: When sound waves enter the cochlea, they cause the fluid known as endolymph to move. High-frequency sounds (which correspond to high pitch) create traveling waves that peak near the base of the cochlea. In contrast, low-frequency sounds (associated with low pitch) cause waves that peak further along the membrane, towards the apex of the cochlea. Thus, the location of the peak in wave activity on the basilar membrane allows the cochlea to identify the pitch of a sound.

Loudness Perception

The loudness of a sound is related to its amplitude rather than its frequency:

1. Amplitude: In auditory terms, amplitude refers to the height of the sound wave. Higher amplitude sound waves result in louder sounds, while lower amplitude waves correspond to softer sounds.

2. Cochlea Response: When sounds enter the cochlea, greater amplitude leads to more vigorous movement of the basilar membrane. This increased movement stimulates more hair cells (sensory receptors) along the cochlea, sending stronger signals to the brain, thus indicating that the sound is loud. Conversely, softer sounds with lower amplitude cause less displacement of the basilar membrane and stimulate fewer hair cells, resulting in a perception of lower loudness.

In summary, the cochlea distinguishes high pitch from low pitch based on the location of the wave peak along the basilar membrane (with high frequency sounds peaking near the base and low frequency sounds peaking at the apex) and perceives loudness through the amplitude of the sound waves, affecting how much the basilar membrane moves and how many hair cells are activated.