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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Locomotion Know More

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  • Properties of Skeletal Muscles:
    1) Skeletal muscles are made up of a number of muscle fibres.
    2) When these muscle fibres get stimulated, they show different types of responses.
  • Threshold Stimulus:
    1) It is the minimum intensity of stimulus which is necessary for the contraction of a muscle fibre.
  • All or None Response:
    1) When the stimulus is equal or more than that of the threshold value, the muscle fibre contracts.
    2) It contracts with a maximum force and does not depend on the strength of the stimulus.
    3) On the other hand, it does not contract if the strength of the stimulus is below the threshold value.
  • Single Twitch: When a single stimulus is applied to a muscle fibre, it gives a single contraction, also known as a single twitch or muscle twitch.
  • Tetanus: When a number of stimuli are given to a muscle fibre in succession, it remains in a state of sustained contraction which is known as tetanus.
  • Fatigue:
    1) The muscle fibre cannot remain in the state of tetanus indefinitely so if the stimulus continues, there is a decline in the force of contraction and ultimately it comes to zero.
    2) The muscle fibre then fails to respond to further stimuli and get fatigue.
    3) When the muscle fibre does not get enough oxygen it starts respiring anaerobically.
    4) The muscle fatigue occurs due to accumulation of lactic acid which is produced as a result of anaerobic respiration.
    5) The muscle fibre starts working again after proper rest.
    6) Muscle fatigue can occur after a strenous physical exercise.
  • Structure of Skeletal/Striated Muscles:
    1) A striated muscle is made up of a number of muscle fibres.
    2) Each muscle fibre is made up of a number of myofibrils.
    3) The myofibrils consists of alternate dark and light bands.
    4) The dark bands are called A bands and the light bands, I bands.
    5) These bands contain thin actin filaments and thick myosin filaments.
    6) A dark line called Z line is present at the centre of I band and a lighter region called H band is present at the centre of A band.
    7) Sarcomere is the area which is present between the two Z lines.
    8) Sarcomere is the structural and functional contractile unit of a myofibril.
  • Sliding Filament Theory of Muscle Contraction: This theory was proposed by two groups which were headed by H.E. Huxley and A. F. Huxley in 1954.
    These scientists proposed this theory on the basis of the following observations:

1.      During muscle contraction, length of A band remains constant.

2.      The length of I band decreases.

3.      The H zone becomes shorter and ultimately disappears.

4.      A thicker line called as M line appears in a fully contracted muscle.

5.      The length of sarcomere also decreases due to decrease in the length of I band.

  • Red Muscle Fibres:
    1) These fibres are dark red in colour due to the presence of myoglobin. They are thin and slow acting.
    2) They possess a large number of mitochondria.
    3) They are specialised for sustained work over a long period of time but at a slow rate.
    4) They do not get fatigue easily.
  • White Muscle Fibres:
    1) These fibres are white/light in colour due to absence or presence of little amount of myoglobin.
    2) They possess less number of mitochondria.
    3) They are thicker and fast acting.
    4) They are specialised for fast and strenous physical work but for a short duration.
    5) They get fatigue easily.

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