Hearing as Humans

Sound and Hearing

Introduction

  • Humans are constantly exposed to various sounds, including environmental noise, verbal communication, and internal body noises.

Sound Examples

  • Examples of sounds include music and alerts to avoid danger.

What is Sound?

  • Sound involves vibration, pressure, and the movement of molecules.
  • Air molecules, like nitrogen and oxygen, surround us.
  • Sound originates from the vibration of objects, creating pressure waves.
  • Examples: vibrations of guitar strings, vocal cords, or plastic.

Sound in Space

  • Space is a vacuum, lacking molecules, hence no sound transmission.

Ear Anatomy and Hearing Process

  • Outer Ear: Directs sound waves.
  • Ear Canal: Funnels sound to the eardrum.
  • Eardrum (Tympanic Membrane): Vibrates in response to sound waves.
  • Middle Ear: Contains three tiny bones (ossicles) that amplify vibrations.
  • These bones are the smallest in the body and can fit on a quarter.
  • Cochlea: Converts sound waves into electrical signals.
  • Resembles a snail and is filled with cells.
  • Sound waves enter the ear, causing the eardrum to vibrate.
  • Vibrations are transferred to the ossicles, which activate cells in the cochlea.
  • Cochlea cells send signals to the brain via the cochlear nerve.

Differentiating Sounds

  • Different vibration speeds create different sound waves.
  • Low frequency: Slow vibrations, such as a cow's vocal cords.
  • High frequency: Fast vibrations, such as a cricket rubbing its wings.

Sound Waves

  • Represent pressure waves of molecules.
  • Peaks: Areas of high pressure with many molecules.
  • Valleys: Areas of low pressure with fewer molecules.

Sound Characteristics

  • Different vibration speeds create different frequencies of pressure waves, leading to different sounds.
  • Sound wave shape also contributes to the sound.
  • Loudness depends on the energy from the sound source.
  • Low energy: Low amplitude sound wave.
  • High energy: High amplitude sound wave, same waveform shape.

Human Hearing Range

  • Humans have a limited audible range.
  • Dog whistles and elephant rumbles are outside this range.
  • Light waves travel much faster than sound waves.

Hearing Assistance

  • Hearing aids: Amplify sound waves.
  • Cochlear implants: Send electrical signals directly to the cochlear nerve, bypassing damaged ear structures.

Detailed Hearing Process

  • Sound waves are directed by the pinna into the ear canal.
  • The eardrum vibrates.
  • Vibrations are transferred to the three tiny bones.
  • Mechanical energy is transferred to the cochlea at the oval window.
  • Hair cells inside the cochlea move and trigger electrical signals to the brain.

Sound Processing in the Brain

  • Signals from the cochlea travel a considerable distance before reaching the auditory cortex.
  • Complex processing occurs before reaching the auditory cortex.

Phone Use and Hearing

  • Preference for holding the phone on the right or left side of the head varies among individuals.

Age-Related Hearing Loss (Presbycusis)

  • Presbycusis is age-related hearing loss.
  • Using loud music or headphones to compensate can further damage hearing.

Earwax and Ear Cleaning

  • Avoid cleaning ears with cotton swabs.
  • Earwax (cerumen) is beneficial for ears.
  • It gathers dead skin cells, hair, and dirt.
  • Cotton swabs can push earwax back into the ear, causing infections or puncturing the eardrum.
  • Pressing on the ear can trigger a cough reflex, which is checked in cases of chronic cough.

Conductive Hearing Loss

  • Results from a deformation, malfunction, or obstruction in the outer or middle ear.
  • Prevents low to moderate intensity sounds from being heard.
  • Higher intensity sounds are perceived as softer than normal.
  • Examples include:
    • Earwax buildup
    • Fluid in the ear
    • Foreign objects in the ear