MICROANATOMY

Detailed explanation-1: -Individual muscle fibers contract in an all or nothing phenomenon, but whole can contract in a graded phenomenon. This is achieved by altering the number of motor units activated in the whole muscle.

Detailed explanation-2: -The ‘All or None’ Law Each fibre within a motor unit contracts according to the all or none law. This principle states that when a motor unit receives a stimulus of sufficient intensity to bring forth a response, all the muscle fibres within the unit will contract at the same time, and to the maximum possible extent.

Detailed explanation-3: -So, the correct answer is ‘A-Band remains constant’.

Detailed explanation-4: -Answer and Explanation: The statement that is false is d. sarcomeres increase in length during contraction. Sarcomeres are the smallest contractile units of muscles and they actually shorten, which causes muscle contraction.

Detailed explanation-5: -A muscle fiber either contracts fully or it doesn’t contract at all. The number of fibers that contract determines the strength of the muscular force. When more fibers contract at the same time, the force is greater.