Audition

• What does the ear capture?

  Sound waves
• How does the ear respond to sound waves?

  It vibrates due to sound waves
• What are the functions of the external auditory canal?

  • Collecting sound waves
  • Enhancing sound waves
  • Transmitting sound waves
  • Acting as a resonating chamber
• What are the three bones in the middle ear called?

  Malleus, Incus, and Stapes
• What is the role of the tensor tympani muscle?

  It pulls the malleus and tympanic membrane inwards
• What does the stapedius muscle do?

  It pulls the stapes away from the oval window
• What are the properties of the middle ear?

  Attenuation reflex and impedance matching
• What is the function of the tympanic reflex?

  It protects against excessive sound stimulation
• Why does the tympanic reflex fail to protect against brief intense sounds?

  Reflex time is too short for protection
• What are the functions of the middle ear?

  • Converts low pressure, high amplitude waves into high pressure, low amplitude waves
  • Mechanism of impedance matching:
  • Lever action of middle ear ossicles
  • Larger area of tympanic membrane than stapes foot plate
• How does the area difference between the tympanic membrane and stapes foot plate affect sound?

  It increases pressure over the oval window
• What is the surface area of the tympanic membrane?

  55 mm²
• What is the area of the foot plate of the stapes?

  3.2 mm²
• How much does the sound wave amplification occur due to the middle ear?

  17 times
• What are the two types of fluids in the inner ear?

  • Perilymph: fluid in vestibular and tympanic ducts, similar to plasma
  • Endolymph: fluid in cochlear duct, rich in K+, low in Na+
• What type of cells secrete endolymph?

  Intermediate cells
• What is the process of sound transduction in the ear?

  • Sound waves captured by the ear
  • Vibrations transmitted through the middle ear
  • Fluid movement in the inner ear
  • Conversion of sound waves into neural signals
• What theory explains how sound travels through the basilar membrane?

  Travelling wave theory of hearing
• Where do high frequency sounds transmit on the basilar membrane?

  To the stiff part of the basilar membrane
• Where do medium frequency sounds transmit on the basilar membrane?

  To the middle of the basilar membrane
• Where do low frequency sounds transmit on the basilar membrane?

  To the flexible part of the basilar membrane
• What is air conduction in hearing tests?

  • Assesses sensitivity through outer, middle, inner ear
  • Signal transmitted to the brain cortex
  • Testing may use headphones or insert earphones
• What is bone conduction in hearing tests?

  • Assesses sensitivity through skull bones
  • Signal transmitted to cochlea and auditory pathways
  • Bypasses outer and middle ear
• What is masking in hearing?

  It raises the threshold of hearing one sound
• Why is sound localization important?

  It helps detect sound sources for survival
• Which parts of the brain are responsible for sound localization?

  Cerebral cortex and medial geniculate body
• What is deafness?

  Reduction in hearing ability
• What are the two main types of deafness?

  1. Conductive deafness

  • Interference with sound conduction to cochlea

  1. Nerve deafness (Permanent)

  • Interference with nerve impulse transmission
• What causes conductive deafness?

  Interference with sound conduction from air to cochlea
• What are some causes of conductive deafness?

  • Obstruction of external ear canal
  • Damage to tympanic membrane
  • Infection of the middle ear
  • Otosclerosis
  • Blockage of Eustachian tube
• What is nerve deafness caused by?

  Interference with nerve impulses from cochlea
• What are the main causes of nerve deafness?

  1. Damage to basilar membrane or organ of Corti
  2. Damage to cochlear nerve
  3. Meniere's syndrome
  4. Extensive lesions of auditory pathway
• What can cause damage to the basilar membrane?

  Prolonged use of antibiotic streptomycin
• What is Meniere's syndrome?

  Increase of pressure of the endolymph
• What can cause damage to the cochlear nerve?

  Severe head injuries or brain tumors
• How does conductive deafness differ from nerve deafness?

  Conductive deafness affects sound conduction, nerve deafness affects nerve impulses