Auditory system

Question 1

What is sound?

Answer 1

Repetitive variations in a medium, such as air. Sound cannot exist without a medium (e.g., no sound on the moon).

Question 2

What determines the frequency and amplitude of sound?

Answer 2

Frequency: Number of cycles per second (measured in Hertz, Hz), determines pitch.

Amplitude: Difference in air pressure from baseline to peak of a wave (measured in Decibels, dB), determines loudness.

Question 3

What is timbre?

Answer 3

The quality of sound, related to the characteristics of the sound wave.

Question 4

What are the three main parts of the auditory system?

Answer 4

Outer Ear: Collects sound waves.

Middle Ear: Amplifies sound using ossicles (malleus, incus, stapes).

Inner Ear: Converts mechanical energy to electrochemical signals via the cochlea.

Question 5

What is the function of the ossicles in the middle ear?

Answer 5

They amplify sound by overcoming the impedance mismatch between air and cochlear fluid, increasing sound pressure by ~34 dB.

Question 6

What is the cochlea’s role in hearing?

Answer 6

Converts sound vibrations into fluid motion.

Hair cells in the Organ of Corti transduce vibrations into electrical signals.

Question 7

What is tonotopy?

Answer 7

Spatial mapping of sound frequency along the basilar membrane:
High frequencies: Near the base.
Low frequencies: Near the apex.

Question 8

Outline the pathway from the cochlea to the auditory cortex.

Answer 8

1) Cochlear nucleus.
2) Superior olivary complex.
3) Lateral lemniscus.
4) Inferior colliculus.
5) Medial geniculate nucleus.
6) Auditory cortex.

Question 9

What is the function of the auditory cortex?

Answer 9

Processes sound features, with “what” and “where” streams for identifying and localizing sounds.

Question 10

What are the two types of hair cells, and their functions?

Answer 10

Inner Hair Cells (IHCs): Primary sensory receptors, sending signals to the brain.

Outer Hair Cells (OHCs): Amplify sound by adjusting basilar membrane vibrations.

Question 11

How do hair cells transduce sound?

Answer 11

Stereocilia bending opens TRPA1 channels, allowing K+ influx, leading to cell depolarization and neurotransmitter release.

Question 12

What are the types of hearing loss?

Answer 12

Conductive: Obstruction in the outer or middle ear.
Sensorineural: Damage to hair cells or auditory nerves.
Mixed: Combination of conductive and sensorineural.

Question 13

What treatments exist for hearing loss?

Answer 13

Hearing aids: Amplify sound for remaining hair cells.

Cochlear implants: Stimulate auditory neurons directly.

Emerging therapies: Gene therapy, stem cells, molecular therapy.

Question 14

What is interaural time difference?

Answer 14

The difference in sound arrival time between ears, aiding in sound localization.

Question 15

What is the cocktail party effect?

Answer 15

The ability to focus on a single sound source in a noisy environment, which may be impaired in Central Auditory Processing Disorder (CAPD).

Question 16

What causes tinnitus?

Answer 16

Perception of sound without external stimulus, possibly due to peripheral or central auditory issues.

Question 17

What mechanisms contribute to sound force amplification in the middle ear?

Answer 17

Area Ratio: Tympanic membrane to stapes footplate (20:1).
Lever Action: Ossicles amplify force (1.3:1).
Buckling of Tympanic Membrane: Doubles pressure.

Question 18

Why is impedance matching important?

Answer 18

It ensures efficient sound transmission from air to the fluid-filled cochlea, overcoming a ~30 dB loss.

Question 19

What are the three fluid-filled cavities in the cochlea?

Answer 19

Scala vestibuli (s.v.)
Scala media (s.m.)
Scala tympani (s.t.)

Question 20

What separates the cochlear compartments?

Answer 20

Reissner’s membrane separates scala vestibuli from scala media.
Basilar membrane separates scala media from scala tympani.

Question 21

what is the name of the fluid in the scala vestibuli and the scala tympani and what are the proportions of K+ and Na+

Answer 21

perilymph
high Na+ and low K+

Question 22

what is the name of the fluid in the scala media

Answer 22

endolymph
high K+ and low Na+

Question 23

How do hair cells differentiate sound frequencies?

Answer 23

Basilar membrane properties vary along its length.

High frequencies activate hair cells near the base; low frequencies activate cells near the apex.

Question 24

What is the role of outer hair cells in the cochlear amplifier?

Answer 24

Adjust basilar membrane stiffness.

Enhance sensitivity and frequency selectivity by changing length in response to sound.

Question 25

What are the two frequency coding mechanisms in the auditory nerve?

Answer 25

Place Code: Based on the location of maximum basilar membrane vibration.
Temporal Code: Neurons fire in sync with sound wave cycles, effective for frequencies < 5 kHz.

Question 26

What is the volley principle?

Answer 26

Groups of neurons work together to encode frequencies higher than a single neuron can process (>1 kHz).

Question 27

What is binaural interaction, and where does it occur?

Answer 27

ntegration of signals from both ears to process spatial sound information.
Occurs in the superior olivary complex and higher auditory centers.

Question 28

What are the key functions of the inferior colliculus?

Answer 28

Integrates auditory input.
Processes sound localization and spatial mapping.
Relays information to the medial geniculate nucleus.

Question 29

What is Central Auditory Processing Disorder (CAPD)?

Answer 29

A condition where the brain struggles to process auditory information, affecting localization, discrimination, and temporal aspects of sound.

Question 30

What are the common causes of tinnitus?

Answer 30

Exposure to loud noises.
High blood pressure.
Medications (e.g., aspirin in high doses).
Stress and fatigue.

Question 31

What are the speech-related areas of the brain?

Answer 31

Broca’s Area: Produces speech; damage causes expressive aphasia.
Wernicke’s Area: Understands speech; damage causes receptive aphasia.

Question 32

How do cochlear implants work?

Answer 32

Bypass damaged hair cells to stimulate spiral ganglion neurons directly.
Utilize the cochlea’s tonotopic arrangement to encode different frequencies.

Question 33

What are the emerging strategies for treating hearing loss?

Answer 33

Gene Therapy: Repairs genetic defects causing hearing loss.
Stem Cell Therapy: Replaces damaged hair cells.
Molecular Therapy: Promotes regeneration of auditory cells.