Question

In muscle contraction, sarcomeres become shorter. Which of the following does not occur in this process.
A. Z lines comes closer
B. A band shortens
C. I band Shortens
D. H band shortens

Answer 1

Hint: Muscle cells are some kind of special cell for contraction providing movement and motion of the body such as walking, lifting and many more things, like to facilitate the process digestion and respiration. Human body possesses different kinds of muscles like skeletal muscles, cardiac muscles, smooth muscles and striated muscles.

Complete answer:
The muscle tissue is formed of contractile protein called actin which is globular protein which interacts with myosin for the muscles contraction. Skeletal muscle attached to the bone that allows movement. Skeletal membrane outer layer is known as sarcolemma, which is the site of action potential that triggers muscle contraction.

Sarcolemma covered the number of muscles fibre. The repeating band of actin and myosin protein give a striated appearance of muscles. The dark A and Light I bands repeat along with myofibrils. The each I band runs vertically through the middle known as Z line and the Z disc mark as the border unit the called as sarcomeres, which is a functional unit of skeletal muscles.

The thick filament present in A band of myofibrils and thin filament attach to protein in Z disc called alpha – actinin.

The shortening of sarcomere causes muscle cells to contract. The thick and thin filament slide by one another, that shorten the sarcomere not filament, which remains in same length, which represent the A band. The contraction mechanism is binding of myosin to actin that form the cross bridge which generates filament movement.

So that during the muscles contraction the I band shortens up along with the H band and the Z line comes closer due to riding over filament, but the A band does not shorten up it will remain the same in size during contraction.

Hence, the correct answer is option (B).

Note: Muscles are the only tissue in the body except the liver where ATP is stored to quickly regulate the muscles movement and do not share its energy with other organs as the liver does. Intensive exercise leads to accumulation of lactic acid in the muscle due to insufficient utilization of oxygen.