Auditory Sensory System Notes

Anatomy of the Ear

• Outer Ear

  • Includes the visible part of the ear and the ear canal.

• Middle Ear

  • Contains three tiny bones: hammer (malleus), anvil (incus), and stirrup (stapes) that concentrate vibrations from the eardrum.

• Inner Ear

  • Contains the cochlea, semicircular canals, and vestibular sacs, which are crucial for hearing and balance.

Sound Waves

• Definitions

  • Frequency: Number of complete wavelengths passing a point in a given time, affecting the pitch.

  • Amplitude: Determines perceived loudness of sound waves.

• Measurement

  • Measured in decibels (dB).

  • 0 dB: Absolute threshold of hearing; exposure above 85 dB can lead to hearing loss.

Process of Hearing

1. Sound Wave Entry: Sound waves strike the eardrum.

2. Vibration Transmission: Vibrations pass through the middle ear bones to the cochlea.

3. Fluid Movement: In cochlea, vibrations jostle fluid causing ripples in the basilar membrane.

4. Hair Cell Activation: Movement of hair cells triggers impulses in nerve cells.

5. Auditory Nerve: Carries messages to the thalamus and then to the auditory cortex in the brain.

Types of Hearing Loss

• Sensorineural Hearing Loss

  • Most common; caused by damage to cochlea's receptor cells or auditory nerve.

  • Often linked to heredity, aging, or exposure to loud noise.

• Conduction Hearing Loss

  • Less common; caused by damage to the mechanical system conducting sound to the cochlea.

• Cochlear Implant

  • Device converting sounds into electrical signals, stimulating the auditory nerve.

Theories of Pitch Perception

• Place Theory

  • Correspondence between pitch we hear and the location of stimulation on the cochlea's membrane.

• Frequency Theory

  • Rate of nerve impulses matches the frequency of a tone, aiding in pitch perception.

• Combination

  • Discussion about how both theories contribute to our understanding of pitch across frequencies.

Sound Localization

• Determines sound's location based on timing and intensity differences received by both ears.

• Right ear receives sound more intensely and slightly sooner when sound comes from the right side.