12th Zoology

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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