Question

Assertion [A]: All muscles follow “all or none” principle.

Reason [R]: All muscles fibers contract either fully or do not contract at all depending upon the threshold stimulus availability.

• A. Assertion [A] is True and Reason [R] is False.
• B. Reason [R] is True and Assertion [A] is False.
• C. Assertion [A] is True and Reason [R] is True and is a correct explanation to [A]
• D. Assertion [A] is True and Reason [R] is True but is not a correct explanation to [A]

Answer 1

The correct option is C

Assertion [A] is True and Reason [R] is True and is a correct explanation to [A]

The magnitude of the action potential set up in any single nerve fiber is independent of the strength of the exciting stimulus, provided the latter is adequate. An electrical stimulus below threshold strength fails to elicit a propagated spike potential. If it is of threshold strength or over, a spike (a nervous impulse) of maximum magnitude is set up. Either the single fiber does not respond with spike production, or it responds to the utmost of its ability under the conditions at the moment. This property of the single nerve fiber is termed the all-or-none relationship. This relationship holds only for the unit of tissue; for nervous tissue the unit is the nerve cell, for skeletal muscle the unit is the individual muscle fiber and for the heart the unit is the entire auricles or the entire ventricles.