SENSORY SYSTEMS—AUDITORY

What is the function of the pinna in the auditory system?

The pinna serves to collect sound and assist in vertical sound localization.

What role do the ossicles play in the middle ear?

They amplify sound as it moves from air to fluid and transmit vibrations from the tympanic membrane to the oval window.

What does the basilar membrane do?

It separates the scala media and scala tympani, and its variable flexibility allows it to respond to different sound frequencies.

How does sound intensity get encoded in the auditory system?

Intensity is encoded by the number of activated auditory fibers and the rate of action potentials in each fiber.

What is the composition of endolymph in the cochlea?

Endolymph contains low sodium (Na+) and high potassium (K+) concentrations.

How do inner hair cells transduce sound?

Sound waves deflect the stereocilia on inner hair cells, causing the opening/closing of K+ channels, leading to depolarization and neurotransmitter release.

What distinguishes the responses of the apex and base of the basilar membrane?

The apex responds to low frequencies due to being wide and floppy, while the base responds to high frequencies as it is rigid and narrow.

What mechanism helps the brain locate sound direction for low frequencies?

Interaural time delay is used, where the brain compares the time it takes for sound to reach each ear.

What is population coding in the auditory system?

Population coding is the activation of a group of hair cells that convey information about a stimulus frequency, especially for low and medium frequencies.

What is the role of outer hair cells?

Outer hair cells amplify sound in the cochlea and contribute to the transduction process by altering the basilar membrane's characteristics.

What is the function of the pinna in the auditory system and how does its structure contribute to sound localization?

The pinna serves to collect sound waves from the environment and assists in vertical sound localization by its unique shape, which affects how sound waves enter the ear.

What role do the ossicles play in the middle ear, and how does their arrangement affect sound transmission?

The ossicles (malleus, incus, and stapes) amplify sound vibrations as they move from air to the fluid-filled cochlea, effectively transmitting these vibrations from the tympanic membrane to the oval window by their lever action.

How does the basilar membrane's variability in structure affect its response to different sound frequencies?

The basilar membrane's variable flexibility allows it to vibrate at different locations depending on the frequency of sound: lower frequencies activate the apex and higher frequencies activate the base.

Explain the process of encoding sound intensity in the auditory system and the implications for hearing perception.

Sound intensity is encoded by the number of activated auditory fibers and the frequency of action potentials in these fibers, which influences the perception of loudness.

What distinguishes the properties of endolymph in the cochlea, and why are these properties essential for sound transduction?

Endolymph is characterized by low sodium (Na+) and high potassium (K+) concentrations, which are essential for creating the electrochemical gradient necessary for hair cell depolarization during sound transduction.

Describe how inner hair cells transduce sound waves into electrical signals, indicating the importance of stereocilia.

Inner hair cells transduce sound by having their stereocilia deflect with sound waves, which opens potassium channels and leads to depolarization and neurotransmitter release, ultimately sending signals to the brain.

Compare the responses of the apex and base of the basilar membrane and discuss their relevance for auditory perception.

The apex, being wide and floppy, responds to low frequencies, while the base, which is narrow and rigid, responds to high frequencies, allowing for a wide frequency range to be perceived by the auditory system.

What is the mechanism of interaural time delay, and how does it aid in locating sound direction for low frequencies?

Interaural time delay helps the brain locate sound direction by comparing the arrival time of sound at each ear, which is particularly effective for low-frequency sounds that have longer wavelengths.

Discuss population coding in the auditory system and its significance for auditory perception at different frequency ranges.

Population coding involves the activation of a group of hair cells that conveys information about a specific frequency, especially pertinent for low and medium frequencies, allowing the auditory system to determine pitch.

What is the function of outer hair cells, and how do they enhance the auditory process within the cochlea?

Outer hair cells amplify sounds by changing their length in response to sound waves, enhancing the movement of the basilar membrane and improving overall sensitivity to sound transmission.