Lecture Notes: How We Hear and Maintain Balance

Introduction

• Exploration of simultaneous enjoyment of music and science
• Focus on the process of hearing and equilibrium

Understanding Sound

• Definition: Sound is a series of vibrations that travel through the air, beating against the eardrum.
• Process:
  • Vibrations move tiny bones, pushing internal fluid against a membrane.
  • This triggers tiny hair cells to stimulate neurons, sending action potentials to the brain.

Anatomy of the Ear

• Three Major Areas:
  • External Ear: Catches sound waves.
  • Middle Ear: Amplifies sound waves.
  • Inner Ear: Converts vibrations to electrical impulses and maintains equilibrium.
• External Ear Components:
  • Pinna/Auricle: Elastic cartilage that catches sound waves.
  • Auditory Canal: Funnels sound towards middle and inner ear.

Middle Ear

• Tympanic Membrane: Eardrum vibrating in response to sound.
• Auditory Ossicles:
  • Bones: Malleus (hammer), Incus (anvil), Stapes (stirrup)
  • Function to amplify sound waves to move inner ear fluid.

Inner Ear

• Labyrinth: Complex structure for hearing and balance.
• Cochlea:
  • Snail-shaped, contains chambers and membranes for sound transduction.
  • Basilar Membrane: Reads sound and communicates to nervous system via organ of corti.
  • Organ of Corti: Contains hair cells that convert vibrations to electrical signals.
• Process of Sound Transduction:
  • Pressure waves cause basilar membrane to vibrate.
  • Vibration excites hair cells, leading to graded and action potentials.
  • Signals travel via cochlear nerve to cerebral cortex.

Equilibrium and Balance

• Vestibular Apparatus:
  • Fluid and sensory hair cells detect head movement.
  • Semicircular Canals: Detect head rotation in different planes.
• Function of Vestibular Apparatus:
  • Detects motion and acceleration of head.
  • Information sent to brain for balance.

Sensory Conflicts and Motion Sickness

• Examples: Spinning or being on a rocking boat causes sensory conflict.
• Cause of Motion Sickness:
  • Conflict between vestibular senses and visual/sensory input.
  • Leads to confusion and motion sickness.

Conclusion

• Summary of how hearing and balance are achieved.
• Acknowledgments of contributors to the Crash Course episode.

Additional Resources

• Mention of Patreon for supporting Crash Course.
• Filming and production credits.