2. Auditory System

Question 1

What are the basic components of the auditory system?

Answer 1

-Outer ear
-Middle ear
-Inner ear
-Cochlea
-Neural pathways to the brain.

Question 2

What parameters define a sound wave?

Answer 2

Sound waves are defined by their frequency and amplitude.

Question 3

Explain the concept of amplitude and its relation to sound loudness

Answer 3

Amplitude corresponds to the loudness of a sound.
-A large amplitude results in a loud sound
-Small amplitude produces a quiet sound.

Question 4

What does frequency represent in sound waves, and how does it affect pitch?

Answer 4

Frequency corresponds to the pitch of a sound.
-High-frequency sounds have more peaks, resulting in a high pitch
-Low-frequency sounds have fewer peaks and a low pitch.

Question 5

Fourier Transforms

Answer 5

Complex sounds can be broken down into simpler (sinusoidal) components through Fourier Transforms.

Question 6

What challenges does the auditory system face in detecting and coding sound amplitudes and frequencies?

Answer 6

Challenges in detecting and coding sound amplitudes and frequencies due to the complexity of sounds, background noise, dynamic range, and the need to adapt to different sound contexts, among other factors.

Question 7

How does the brain dynamically modulate auditory processing in a context-specific manner?

Answer 7

-Adjusting the sensitivity and selectivity of auditory neurons based on the specific acoustic environment
-Optimizing the detection and discrimination of relevant sound features while filtering out irrelevant information.

Question 8

Outer Ear

Answer 8

-Includes the pinna
-Helps collect and amplify sound.
-It also differentially filters sound waves based on their source’s elevation, aiding in sound localization.

Question 9

Middle Ear

Answer 9

-Prevents sound reflection.
-Transforms sound vibrations into larger ones, suitable for the inner ear.
(This is necessary because sound travels through air, while the inner ear’s sensors are in an aqueous environment.)

Question 10

Inner Ear

Answer 10

Consists of the membranous labyrinth within a bony labyrinth.
-Bony labyrinth is filled with perilymph
-Membranous labyrinth contains high potassium endolymph.
Vibrations are passed from the oval window to the cochlea.

Question 11

Cochlea

Answer 11

Partitioned by Reisner’s membrane and the basilar membrane, creating fluid-filled compartments: scala vestibuli, scala media, and scala tympani.
It contains the organ of Corti and is essential for sound transduction.

Question 12

Hair Cells

Answer 12

Transform mechanical energy into electrical energy by generating APs in ganglion cells when sound vibrations cause the stereocilia to move.

Question 13

Place Code

Answer 13

The place code is the cochlea’s mechanism for encoding different sound frequencies.
-Cochlear implants stimulate different cochlear regions based on this code when hair cells are not functional.

Question 14

Sound Localization

Answer 14

The ability to determine the direction of a sound source.
-Crucial for situational awareness and spatial orientation.

Question 15

How do interaural time differences (ITDs) contribute to sound localization?

Answer 15

ITDs are time disparities between sound arrivals at the two ears, helping the brain determine the direction of a sound source.
-MSO is crucial for sound localization based on ITDs

Question 16

How do interaural level differences (ILDs) contribute to sound localization?

Answer 16

ILDs are differences in sound intensity between the two ears, which the brain uses to locate sound sources, especially in the horizontal plane.

Question 17

How does lateral inhibition (two-tone suppression) affect auditory processing?

Answer 17

Lateral inhibition enhances contrast between excitatory and inhibitory responses, facilitating better sound localization.

Question 18

What neural mechanisms support the Jeffress Model for ITD processing?

Answer 18

Axonal path length differences and specific branching patterns in the auditory system cause specific neural delays, facilitating ITD processing.

Question 19

How does the cochlea analyze different sound frequencies, and what is the role of the basilar membrane?

Answer 19

The cochlea analyzes different sound frequencies through a process known as tonotopy. The basilar membrane within the cochlea is crucial for this, as it vibrates in response to specific frequencies, with higher frequencies causing vibrations at the basal end and lower frequencies at the apical end.

Question 20

What are the key components of the cochlea’s partitioning, and how does the cochlea transform sound pressure waves into nerve impulses?

Answer 20

The cochlea is partitioned by Reissner’s membrane and the basilar membrane, creating fluid-filled compartments like Scala Vestibuli, Scala Media, and Scala Tympani. Sound pressure waves are converted into nerve impulses by hair cells located in the Organ of Corti, specifically the inner and outer hair cells.

Question 21

What is the role of hair cells in auditory transduction, and what is the significance of the tectorial membrane?

Answer 21

Hair cells are essential for converting mechanical energy (from sound vibrations) into electrical energy, generating action potentials in ganglion cells. The tectorial membrane plays a role as it moves in response to sound vibrations, initiating the generation of electrical energy in hair cells.

Question 22

How does the basilar membrane facilitate the encoding of different sound frequencies, and what is the concept of place coding?

Answer 22

The basilar membrane varies in stiffness and responds differently to different sound frequencies, higher frequencies affecting the apical end and lower frequencies affecting the basal end. Place coding refers to the mechanism by which the cochlea encodes different sound frequencies based on where they stimulate the basilar membrane.

Question 23

What is the role of spiral ganglion cells (SGCs) in auditory processing, and how do tuning curves relate to their function?

Answer 23

SGCs are the output cells of the spiral ganglion and are responsible for generating APs in response to specific sound frequencies. Tuning curves represent SGCs’ responsiveness to sound frequencies, indicating their “best frequency” and how their activity varies with sound intensity.

Question 24

What is the neural basis for auditory processing beyond hair cells, and how do ribbon synapses contribute to this process?

Answer 24

Beyond hair cells, the auditory system involves the cochlear nuclei, which process auditory signals. Ribbon synapses play a role in efficiently releasing neurotransmitters in a sustained and regulated manner, which is crucial for transmitting sensory information.

Question 25

Otoferlin

Answer 25

Otoferlin is a protein found in inner hair cells of the cochlea. It plays a crucial role in synaptic vesicle fusion, a process vital for transmitting auditory signals from hair cells to auditory nerve fibers. Mutations in the otoferlin gene can lead to hearing loss.
-Essential for normal hearing.

Question 26

How does otoferlin function as a calcium sensor, and why is this role significant in auditory processing?

Answer 26

Otoferlin is considered a calcium sensor, involved in the calcium-triggered exocytosis of synaptic vesicles. This role is crucial for the continuous release of synaptic vesicles and transmitting auditory information from hair cells to the auditory nervous system.

Question 27

What role do myosin motors play in the adaptation of mechanoelectrical transduction currents in hair cells?

Answer 27

Myosin motors, particularly myosin 1C, are believed to be responsible for the adaptation of mechanoelectrical transduction currents in hair cells. They facilitate the closing of ion channels after mechanical stimulation.

Question 28

What is the significance of the period and phase locking of interaural time differences (ITDs) in the MSO for sound localization?

Answer 28

MSO neurons in the brain process ITDs, and the period and phase locking of these ITDs are essential for determining the direction of a sound source and accurately localizing sounds in space.

Question 29

How do the LSO and medial nucleus of the trapezoid body (MNTB) contribute to interaural level differences (ILDs) and sound localization?

Answer 29

LSO and MNTB play roles in processing ILDs and contribute to sound localization by responding to the differences in sound intensity between the ears, aiding in pinpointing the direction of a sound source.

Question 30

What are monaural and binaural localization cues, and how do they enable humans to localize sounds in space?

Answer 30

Monaural cues are localization cues processed by one ear, including spectral filtering by the pinna and head shadow effects. Binaural cues involve ITDs and ILDs, which help humans precisely locate sounds in space by comparing information from both ears.