Question

The Muscle band that remains unchanged during contraction and relaxation of skeletal muscle is
A. I
B. H
C. A
D. Z line
E. H and Z line

Answer 1

Hint:
Muscle contraction is the stimulation of friction-generating muscle fibre sites. The cessation of muscle contraction is proceeded by muscle relaxation, which would be the return of the muscle fibres to normal low tension-generating state.

Complete step by step answer:
he sarcomeres are what really offer the cardiac and skeletal muscles their striations look, that was first established by Van Leeuwenhoek. Each muscle cell has a cell membrane (sarcolemma) and contains many nuclei along its length. The nucleus is relocated peripherally inside the cross-section of the sarcoplasm, while a huge proportion of longitudinal myofibrils, groups of organised muscle proteins, occupy most of the centre space. Myofibril has several prominent histopathologic markers: The myofibril is comprised of alternate bands. I - bands (isotropic in polarised light) look light in colour and the A-bands (anisotropic in polarised light) seem darker in colour. The A-band encompasses the whole span of a single thick filament. The anisotropic band includes both thin and thick filaments. The A band which is present alternatively in the myofibrils stays untouched during the contraction and relaxation of skeletal muscles.
So, the correct option is (C).

Additional Information
Muscle contraction is defined as isometric if the muscle tension differs but the length of the muscle stays the very same. But on the other hand, muscle contraction is isotonic if muscle tension stays the same throughout the contraction. If the length of the muscle lessens, the compression is concentric, if the muscle is stretched, the contracting is eccentric. In muscle cells, the plasma membrane spreads across the sarcoplasm to encircle each myofibril, creating a T-tubule system. The T-tubules facilitate synchronous contraction of all sarcomeres throughout the myofibril. T-tubules are located at the junction of the A-and I-bands, and their reflectivity is continuous with an extracellular environment. At these junctions, the T-tubules are in frequent proximity with the sarcoplasm, which further forms a circuit around each myofibril.

Note:
Whenever the sarcomere contracts, the Z bands shift nearer together, and also the I band slowly decreases. The band A remains the same width. The thick and thin filaments intersect absolutely at full contraction.