Mechanism of hearing

Mechanism of hearing

Functions of External Ear

Sound waves enter the external auditory meatus, pass along the external eustachian canal and fall on the tympanic membrane (TM). This causes the TM to vibrate. (Mechanism of hearing)

Functions of Middle Ear 

The middle ear is an air filled cavity in the temporal bone which opens via the eustachian tube into the nasopharynx. The auditory tube opens during chewing, swallowing and yawning thus keeping the pressures on both sides of the tympanic membrane equal.

The three auditory ossicles are localised in the middle ear. Of these,
the malleus is attached to the TM, and the stapes to the membranous oval
window on the medial wall. Incus articulates with these two bones. Thus
vibrations of the TM are transmitted to the oval window. As the TM has an
area of 90mm2 and the foot plate of the stapes 3.2mm2 and the lever system
formed by the ossicles multiplies the force 1.3 times. (Mechanism of hearing)

The vibrations of the oval window generate pressure waves in the
fluid filling the vestibular canal. The pressure waves pass to the median canal
and vibrate the basilar membrane. The tympanic canal is connected to a
circular membrane called the round window just beneath the oval window.
This arragement allows the pressure waves to transmit through the cochlear
fluid. (Mechanism of hearing)

Functions of Cochlea

The inner ear (labyrinth) is made up of the cochlea and the vestibule. The cochlear portion of the labyrinth is a tubule coiled 2.75 times. Throughout its length the cochlea is divided into three compartments by the basilar and the Reissner’s membranes. (Mechanism of hearing)

The middle compartment (scala media) contains endolymph and the other two (scala vestibuli & scala tympani) contain perilymph.

Organ of Corti

Located on the basilar membrane is the Organ of Corti which
contains the auditory receptors. Four rows of hair cells arise from the basilar
membrane. (Mechanism of hearing)

Stimulation of hair cells

Movements of the foot plate of the stapes set up a series of waves in the perilymph of the scala vestibuli. This in turn causes vibrations of the vestibular membrane and hence of the endolymph in the scala media. These waves deflect the Reissner’s membrane and this in turn produces disturbances in the basilar
membrane which bend the hairs of hair cells in the organ of Corti. This leads
to development of action potentials in the related nerve fibres which are
transmitted along the auditory nerve. (Mechanism of hearing)

The site of maximum distortion in the organ of Corti is
determined by the frequency of sound, for high pitched sounds the
maximum height of the waves is near the base of the cochlea and for low
pitched near the apex. The extent of distortion is determined by the loudness
of the sound. Interpretation of these impulses is made in the auditory cortex.

Sound waves ® vibrate tymphanic membrane ® movements in ear ossicle
chain ® vibration of oval window ® waves in perilymph (scala vestibuli) ®
waves in endolymph ® deflection in the Reissner’s membrane ® basilar
membrane disturbed ® bending of hair cells ® action potential ®
transmission by auditory nerve. (Mechanism of hearing)

Related Topics in Zoology:

Bio Zoology All Important Topics

  1. Human Physiology Introduction
  2. Nutrition
  3. Carbohydrates Poly hydroxyaldehydes (or) ketones
  4. Proteins (Polypeptides)
  5. Lipids
  6. Vitamins – Functions Of Vitamins
  7. Deficiency of Vitamin
  8. Minerals – Water – Role of water
  9. Balanced diet
  10. Obesity
  11. Digestive System
  12. Dental Caries (Tooth decay)
  13. Root Canal Treatment
  14. Peptic ulcer
  15. Hernia and Types
  16. Appendicitis (Appendix)
  17. Gall Stones
  18. Hepatitis
  19. Fractures – Types of fractures
  20. Mechanism of fracture
  21. Dislocation of joints
  22. Arthiritis
  23. Rickets and Osteomalacia – Orthopedics
  24. Muscles
  25. Mechanism of muscle contraction
  26. Types of muscle contraction
  27. Myasthenia Gravis
  28. Respiration – Process of pulmonary respiration
  29. Mechanism of Breathing
  30. Regulation of Respiration
  31. Pneumonia Tuberculosis Symptoms Treatment
  32. Bronchitis – Acute bronchitis, Chronic Bronchitis Causes
  33. Circulatory System – Functioning of Human heart
  34. Cardiac Cycle
  35. Coronary blood vessel and its significance
  36. Myocardial infarction
  37. Angina pectoris
  38. Angiogram – Angioplasty
  39. Atherosclerosis
  40. Heart block Echo cardiography Heart Valves
  41. Rheumatic Heart Disease (RHD), ICCU – (Intensive Coronary Care Unit)
  42. Blood Pressure
  43. Heart transplantation
  44. Pulse rate
  45. Cardio Pulmonary Resuscitation (CPR)
  46. Blood – Composition of plasma – Blood cells
  47. Clotting of Blood or Haemostasis
  48. Thrombosis
  49. Nervous system Co-ordination systems
  50. The Brain – Fore Brain, Midbrain, Hindbrain
  51. Memory
  52. Sleep – Types of sleep
  53. Stroke – Brain haemorrhage
  54. Alzheimer – Meningitis (Brain fever)
  55. Conditioned reflex
  56. Electroencephalography EEG
  57. Right and Left brain concept
  58. Spinal cord functioning
  59. Chemical co-ordination – Functions of Endocrine glands
  60. Hypothalamus
  61. Pituitary gland – hormone
  62. Hormones of Neurohypophysis – vasopressin
  63. Thyroid gland
  64. Parathyroid Gland
  65. Pancreas
  66. Adrenal gland
  67. Gonads
  68. Receptor Organs – Eye
  69. Photochemistry of Retinal visual Pigments
  70. Errors of refraction
  71. Optometry – Retinopathy
  72. Cataract – Lens Replacement – Glaucoma – Nyctalopia
  73. Eye Infections and Eye Care
  74. Ear
  75. Mechanism of hearing
  76. Defects of the ear
  77. Hearing Aid – Noise pollution
  78. Skin and functions of skin
  79. Melanin functions
  80. Effects of solar radiation / UV radiation – Skin grafting
  81. Dermatitis
  82. Tongue – Mechanism of Stimulation
  83. Excretion Ureotelism Nephron
  84. Mechanism of urine formation
  85. Renal Failure, Dialysis, Kidney Machines
  86. Kidney stone – Kidney transplantation
  87. Diabetes mellitus
  88. Functioning of male reproductive system
  89. Functioning of female reproductive system
  90. Ovulation and fate of the ovum – Menstrual cycle
  91. Fertilization
  92. Birth control

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