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Calcium ion concentration in blood affec...

Calcium ion concentration in blood affects muscle contraction. Does it lead to tetany in certain cases? How will you correlate fluctuation in blood calcium with tetany?

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For the muscle fibre to contract, the binding site on thin filaments must be uncovered. This occurs when `Ca^(2+)` bind to another set of regulatory proteins, called troponin complex which control the position of tropomyosin on the thin filament.
The calcium binding rearranges the tropomyosin, troponin complex, exposing the myosin-binding sites on the thin filament. When`Ca^(2+)` is present in the cytosol, the thin and thick filament slide part each other resulting in muscle contraction.
Similarly, when the `Ca^(2+)` concentration falls, the binding sites get covered and contraction stops.
In case of tetany there occur low calcium levels in body fluid due to diminished function of parathyroid gland. This gland is mainly involved in the secretion of parathyroid hormone which is associated in regulating calcium levels in blood. Tetany results in periodic painful muscular spasm (wild contraction) and tremors.
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Knowledge Check

  • Calcium ions bring about muscle contraction through

    A
    Activation of myosin ATP-ase
    B
    Exposing active sites of actin filaments
    C
    Both A and B
    D
    Mobilisation of food reserve.
  • The steps involved in the mechanism of muscle contraction are given below. Arrange the steps in proper sequential order and select the correct option. I. Release of calcium ions in the sarcoplasm. II. Signal sent by the CNS via a motor neuron. III. Binding of calcium with a subunit of troponin on actin filaments. IV. Generation of the action potential in the sarcolemma. V. Binding of myosin head to the exposed active sites on actin to form a cross-bridge. VI. Inward pulling of ā€˜Z’ line attached to actin causing shortening of the sarcomere. VII. Pulling of the attached actin filaments towards the centre of 'A' band. VIII. Release of neurotransmitter acetylcholine and generation of the action potential in the sarcolemma.

    A
    III, II, V, I, IV, VI, VII, VIII
    B
    II, VIII, IV, I, III, V, VII, VI
    C
    I, VIII, VI, II, V, IV, III, VII
    D
    II, IV, V, I, III, VII, VIII, VI
  • Assertion: Tetany is rapid spasm in muscle. Reason: Tetany is usually caused by an increases in the blood calcium level.

    A
    If both assertion and reason are true and reason is the correct explanation of assertion
    B
    If both assertion and reason are true but reason is not the correct explanation of assertion
    C
    If assertion is true reason is false
    D
    If both assertion and reason are false
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