Lecture 10

Question 1

What are the three main regions of the ear and their functions?

Answer 1

• External ear: Collects and channels sound (auricle, external auditory meatus)
• Middle ear: Amplifies sound (ossicles: malleus, incus, stapes)
• Inner ear: Transduces sound into neural signals (cochlea)

Question 2

What is the function of the tympanic membrane?

Answer 2

Vibrates in response to sound waves and transmits vibrations to the ossicles

Question 3

What are the three ossicles and their connections?

Answer 3

• Malleus: Attached to tympanic membrane
• Incus: Connects malleus to stapes
• Stapes: Attached to oval window

Question 4

What is the acoustic attenuation reflex and which muscles are involved?

Answer 4

• Reflex that dampens loud sounds
• Stapedius (CN VII): pulls stapes away from oval window
• Tensor tympani (CN V3): tenses tympanic membrane

Question 5

What are the three fluid-filled chambers of the cochlea?

Answer 5

• Scala vestibuli (perilymph; low K+)
• Scala media (endolymph; high K+)
• Scala tympani (perilymph; low K+)

Question 6

What is the Organ of Corti and where is it located?

Answer 6

• Located on the basilar membrane in the scala media
• Contains inner and outer hair cells for sound detection and amplification

Question 7

What is the function of inner vs outer hair cells?

Answer 7

• Inner hair cells: Primary sensory receptors for sound
• Outer hair cells: Amplify sound via electromotility

Question 8

How is sound transduced into electrical signals?

Answer 8

1. Basilar membrane vibrates
2. Stereocilia bend against tectorial membrane
3. Ion channels open → K⁺ influx
4. Depolarization → neurotransmitter release → CN VIII activation

Question 9

How is frequency (pitch) encoded in the cochlea?

Answer 9

• High frequencies: Vibrate stiff, narrow base of basilar membrane
• Low frequencies: Vibrate wide, flexible apex

Question 10

How is amplitude (volume) encoded?

Answer 10

• Louder sounds activate more hair cells and more primary sensory neurons
• Each IHC is innervated by 10–20 neurons with different thresholds

Question 11

What is the ascending auditory pathway?

Answer 11

Cochlear nuclei → superior olivary nuclei → nucleus of the lateral lemniscus → inferior colliculus → MGN → auditory cortex

Question 12

What is the role of the superior olivary complex?

Answer 12

• Medial: Localises low-frequency sounds via interaural time differences
• Lateral: Localises high-frequency sounds via intensity differences

Question 13

What is the role of the dorsal cochlear nucleus?

Answer 13

Vertical sound localisation using reflected sound delays

Question 14

What are the functions of the inferior colliculus?

Answer 14

• Integrates auditory input
• Constructs spatial auditory map
• Detects biologically relevant patterns
• Suppresses echoes (precedence effect)

Question 15

What is the function of the primary auditory cortex (A1)?

Answer 15

• Located in Heschl’s gyrus
• Tonotopically maps cochlea
• Processes complex auditory input

Question 16

What are the functions of the secondary auditory cortices?

Answer 16

• Left: Language comprehension (Wernicke’s area)
• Right: Music and emotional interpretation