Ch 5 Pt 4

Hearing, or audition, involves the conversion of sound waves into neural messages.
Cilia (Hair Cells): These highly important structures are located in the cochlea (or cochlea) within the inner ear. They are crucial for determining what is heard.
- Damage to cilia, often due to aging or prolonged exposure to loud noise (as experienced by musicians), causes them to 'get fried' or 'shaven down,' leading to hearing difficulty.
The neural message, converted from sound waves, travels via the auditory nerve to the temporal lobe, where auditory perception occurs.

Auditory Canal: A short tunnel running from the outside of the ear.
- Pinna: The outer, visible part of the ear, made of cartilage. People, and especially animals like dogs, can move it to direct sound. Placing a hand behind the pinna can help to hear better.
Eardrum (Tympanic Membrane): A thin slice of skin that tightly covers the opening into the middle ear, similar to a drum's surface.
- It vibrates when hit by sound waves.
- Not to be confused with specific types of drums like 'timpani drums' (kettle drums, usually brass) or 'steel drums' (from Jamaica).
Middle Ear Ossicles (Tiny Bones): These three tiny bones vibrate in sequence after the eardrum vibrates.
- Hammer: First bone to vibrate.
- Anvil: Vibrates after the hammer.
- Stirrup: Vibrates after the anvil.
Oval Window: Located just outside the cochlea, it receives vibrations from the stirrup.
Cochlea (or Cochlea): A fluid-filled, snail-shaped structure in the inner ear.
- The vibrations from the oval window cause the fluid inside the cochlea to move.
- The movement of this fluid stimulates the cilia (hair cells) within the cochlea.

Sound waves enter the auditory canal, hit the eardrum, causing it to vibrate.
The eardrum's vibrations are transferred through the hammer, anvil, and stirrup.
The stirrup transmits these vibrations to the oval window.
The oval window's movement causes the fluid in the cochlea to move.
The fluid movement stimulates the hair cells (cilia) inside the cochlea.
The electrical signals generated by the hair cells are sent via the auditory nerve to the auditory cortex in the temporal lobe, where sound is perceived.
The strength of the vibration determines various characteristics of sound, including:
- Loudness
- Pitch
- Tone
- Timbre

Vestibular Organs (Semicircular Canals): Located in the inner ear, these organs are arranged on different planes and are filled with fluid. They are responsible for the kinesthetic sense, also known as the sense of balance or somatosensory sense.
Sensory Conflict: This occurs when there is a mismatch between sensory inputs, often between vision and the inner ear's fluid movement.
- Example 1: Spinning: When a child spins, the fluid in the vestibular organs moves. Upon stopping, the fluid continues to move, creating a conflict with visual input and causing dizziness.
- Example 2: Carsickness: When looking out a car window at a rapidly passing world (e.g., 70 \text{ miles an hour} ), the visual input conflicts with the perceived lack of motion by the body, leading to fluid movement in the vestibular organs and causing carsickness.

Decibels (dB): The unit used to measure the loudness of a sound.
Examples of Decibel Levels:
- Tree leaves in a slight breeze: 10 \text{ dB} (very quiet)
- Quiet office: approximately 40 \text{ dB}
- Heavy traffic/subway train: Enters the dangerous zone.
- Amplified rock music: Up to 150 \text{ dB} (immediate danger with prolonged exposure).

Hearing Damage: Prolonged exposure to loud noises can permanently damage the delicate cilia (hair cells) in the cochlea, leading to hearing loss.
**Personal Anecdote from the Professor:
- Early Exposure: As a professional musician, the professor toured extensively for years, playing approximately 150 shows a year, for a total of nearly 1000 shows.
- Early Hearing Loss: By the age of 26 , after years of playing rock music, the professor had already experienced significant hearing loss:
  - 25\% loss in the left ear.
  - 15\% loss in the right ear.
- Exacerbation: Living in Korea for ten years and commuting daily on loud subways further exacerbated the existing hearing damage.
- Tinnitus: In February of 2007 , the professor's ears began ringing constantly and have not stopped since (for 14 years at the time of the lecture). This condition is called tinnitus.
  - Tinnitus is a persistent and often very loud ringing in the ears for which there is no cure.
  - It makes sleeping difficult, often requiring external white noise (e.g., a fan) to mask the ringing.
Public Service Announcement: Be careful with earbud and headphone use. Once hearing damage occurs, it is irreversible.
- The professor expects to go deaf or very close to it later in life due to negligence in youth.