12th Zoology

Mechanism of muscle contraction

Mechanism of muscle contraction

Sliding – filament hypothesis

Hanson and Huxley proposed this hypothesis (1955). According to
this hypothesis, the contractile unit of muscle is made up of two types of
filaments i.e., myosin and actin. These filaments during contraction slide over
one another. It has been observed that both at the time of contraction and
stretching, the length of the ‘A band’ remains constant. The length of the ‘I
band’, on the other hand, changes in accordance with the length of the muscle.

Due to this, the Z discs are pulled together. Thus successive sarcomeres are
pulled. This leads to the contraction of the muscle.

ATP as the source of Energy for contraction

For a muscle in action, energy is required. This energy is released by cleaving ATP molecules to ADP+ Pi. Greater amount of work is performed by the muscle, with greater amount of ATP that is cleaved. This energy binds with active site of actin filament to contract.

Neuro muscular Transmission

The muscles are innervated by myelinated nerve fibres that originate from the spinal cord. The nerve ending makes a junction, called neuromuscular junction. The nerve is connected at the midpoint of muscle fibre so that action potential in the fibre travels in both directions. When a nerve impulse reaches the neuro-muscular junction, a substance called acetylcholine is released. The acetylcholine induces muscle fibre for contraction.

Initiation of muscle contraction

Initiation of contraction of skeletal muscle begins with action potentials in the muscle fibres. These elicit electrical currents that spread to the interior of the fibre, where Ca ions are released from the sarcoplasmic reticulum. The Ca ions inturn initiate the chemical events of the contractile process. This overall process of controlling muscle contraction is called excitation.

Maximum strength of contraction

The maximum strength of contraction of a muscle operating at a normal muscle length is about 3.5 Kg / of muscle.

Changes in muscle strength

When a muscle begins to contract after a long period of rest, its initial strength of contraction may be as little as one half of its maximum strength. It gains strength after 30-50 muscle twitches. Weight lifters apply this to reach maximum capacity.

Muscle Tone

When the muscles are at rest, a certain amount of contraction usually
remains. This residual degree of contraction in skeletal muscles is called
muscle tone. The skeletal muscle tone is the result of nerve impulses from
the spinal cord. These in turn are partially controlled by impulses transmitted from the brain. To some extent, the muscle tone is due to the muscle fibres itself.

Muscle Fatigue ( muscle contraction is diminished)

Prolonged and strong contraction of muscle leads to the state of muscle
fatigue. This is due to muscle glycogen depletion and lactic acid accumulation.
Fatigue probably results from inability of the contractile process and deficient
metabolic process of the muscle fibre.
However, experiments show, that transmission of nerve signals through
the neuromuscular junction can occasionally diminish the prolonged muscle
activity, thus further reducing the power of muscle contraction. It is a well
known fact that non-supply of blood to the muscles leads to almost
complete fatigue within a minute. This is due to non-supply of O2 and
nutrients to the muscles.

Rigor Mortis

Several hours after death all the muscles of the body attain
a state of contracture called Rigor mortis. This is due to complete
depletion of ATP in muscle fibres. The muscle remains in rigor, until the
lysosome enzymes completely destroy all muscle proteins. This will take place
within 15-25 hours after death.

Muscle Pull

Muscle pull is actually a muscle tear. A traumatic pulling of the fibres
produces tear known as strain. This injury can occur due to sudden
stretching of muscle beyond their point of elasticity. While some strains are
the result of high velocity impacts, other types of pull can be due to repetitive movements.

When the muscles are being exerted over a long period of time, they become vulnerable to tearing from a simple change in the position of muscles. Back pain is a common problem, caused by muscle pull.

This may be due to improper posture at the chairs. In these cases, the muscles are tightened over a long time, but the muscles may not tear until something as
simple as reaching for a glass of water occurs.

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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