Lecture Notes: Understanding the Auditory Pathway

[Music]

• Introduction:
  • Exploration of how we hear music and interpret songs.
  • Sound from AirPods are vibrations interpreted by the brain as music.

Understanding Sound

• Sound is composed of vibrations, not actual words or music.
• Vocal cords create vibrations that are interpreted by the ear and brain.

Sound Waves

• Sound Waves: Created by vibrations pushing against air molecules.
• Frequency: Determines pitch (high or low).
  • High frequency = high pitch (waves close together)
  • Low frequency = low pitch (waves spread apart)
• Amplitude: Determines loudness.
  • Higher amplitude = louder sound
  • Lower amplitude = quieter sound

Structure of the Ear

• Comprised of three main parts: outer ear, middle ear, and inner ear.

Outer Ear

• Pinna: Collects sound waves and funnels them into the ear.
• Auditory Canal: Passes sound waves towards the brain for processing.

Middle Ear

• Contains the tympanic membrane (eardrum) and three tiny bones (ossicles).
• Tympanic Membrane: Converts sound waves to vibrations.
  • Begins amplification process needed for inner ear fluid movement.
• Ossicles: Malleus (hammer), Incus (anvil), Stapes (stirrup).
  • Amplify vibrations for the inner ear.

Inner Ear

• Semicircular Canals: Filled with fluid and tiny hair cells aiding balance and posture (vestibular sense).
• Cochlea: Main site for hearing.
  • Shaped like a snail, contains fluid and the organ of Corti.
  • Transduction occurs here, converting sound to electrical signals.

Organ of Corti

• Basilar Membrane: Supports hair cells that convert vibrations to action potentials.
• Sound causes different hair cells to vibrate based on frequency:
  • High frequency = base of cochlea
  • Low frequency = apex of cochlea

Auditory Processing

• Pathway:
  • Sound waves → Tympanic membrane (vibrations) → Ossicles → Oval window → Cochlear fluid → Basilar membrane → Stereocilia (action potential) → Auditory nerve → Brain.
• Auditory Pathway to Brain:
  • Action potentials travel to brainstem, then to thalamus (sensory pit stop), and finally to the auditory cortex located in the temporal lobe.
  • Auditory cortex processes sound, pitch, amplitude, and integrates with memory.

Conclusion

• Understanding involves multiple parts of the brain and ear structures working together to interpret sound.