Question

In the given diagrammatic representation of muscle contraction, identify the process marked as 1, 2, 3, 4 and 5.

A) 1-Cross bridge, 2-Cross bridge formation, 3-Breaking of the cross bridge, 4-Sliding (rotation), 5-ATP
B) 1-Cross bridge, 2-Cross bridge formation, 3-Sliding / rotation, 4-Breaking of the cross bridge, 5-ATP
C) 1-Cross bridge, 2-Breaking of the cross bridge, 3-Sliding/rotation, 4-Cross bridge formation, 5-AMP
D) 1-Cross bridge, 2-Cross bridge formation, 3-Sliding/rotation, 4-ADP, 5-Breaking of the cross bridge.

Answer 1

Hint:
Skeletal muscles are contractile in nature i.e., they contract when exited. This process involves two steps 1) Neurotransmitter transmission. 2) Excitation-contraction coupling. Contraction of skeletal muscles means sliding actin and myosin fibres past each other so that the effective length of myofibril is shortened.

Complete step by step solution:
The above figure represents the sliding filament theory for skeletal muscle contraction. For the contraction to take place, actin and myosin filaments need to be located very close to each other. This Is achieved by springy titin protein that holds actin and myosin close enough to facilitate the proper functioning of sarcomere contractile machinery. This contraction cycle is explained by the sliding filament mechanism.
Myosin heads hydrolyze ATP and become reoriented and energized, after myosin heads bind to actin, forming cross-bridges then myosin heads rotate toward the centre of the sarcomere ( this is also known as power stroke) then myosin heads bind ATP and the cross-bridges detach from actin.
So 1 represents cross-bridge and 2 represents cross-bridge formation, 3 represents sliding/ rotation of myosin heads, 4 represents the breaking of cross-bridge, and 5 represents ATP to which myosin heads bind.

Option ‘B’ is correct

Note:
Neuromuscular transmission is the process by which the brain signals a muscle to contract. Its steps are: The action potential to initiate skeletal muscle contraction is delivered to the muscle where motor neuron fibers innervate the muscle fiber. This point of a nerve-muscle contract is called the neuromuscular junction or end motor plate.