12th Zoology



Muscles are elastic in nature. They are capable of contraction in
response to stimulus from the central nervous system.

The muscle cells function like biological machines that convert chemical energy into mechanical work.

The mechanical work involves various movements including vital processes like contraction of the heart and blood vessels.

Approximately 40% of the body is skeletal muscle and almost 10% is smooth
and cardiac muscles.

Structure of a skeletal muscles:

A striated muscle is composed of many fibres arranged in bundles. The diameter of each fibre varies from 10 to 100 microns. The length of fibres ranges from 1 to 20mm. Each fibre is surrounded by a membrane, called the sarcolemma.
Each muscle fibres is made up of 4 to 20 thread-like structures called myofibrils. They are parallel to each other. The myofibrils are 1 to 3 micron in diameter. In between the myofibrils, the sarcoplasm is present. A small segment of the myofibril is called as the sarcomere.

Structure of sarcomere :

When a sarcomere is observed under a microscope, we could see alternative dense ( A band ) and light bands ( I band). The central region of the A band is often less dense and is known as the “H Zone”.

The ‘I band’ is bisected by a dense narrow line, the Z line. Thus each sarcomere includes repeating units between two Z lines in linear order as Z line, I band, A band, I band and next Z line.

Electron microscopic studies have shown that the striations are due
to the regular arrangement of 2 types of protein filaments. ‘A band’ contains
a set of thick filaments formed of the contractile protein myosin. It may
range upto 110 Ao in diameter and 1.5 micron in length.

The second set of thin filaments ( 50 Ao diameter) overlap the long
filaments in ‘A band’. The second set of filaments extend partly in ‘I band’
and partly in ‘A band’. These filaments are formed of a substance called

Myosin, actin, tropomyosin and troponin are the four major proteins
which constitute the contractile machinery of muscle fibre. The energy for
muscle action is provided by ATP molecules.

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

Leave a Reply

Your email address will not be published. Required fields are marked *