Question

Identify the correct statements:
1. The bands are dark and contain myosin.
2. I bands are light and contain actin
3. During the action A band contracts
4. The part between two z lines is a sarcomere
5. The central part of thin filament not overlapped by thick filament is called the H-Zone
A. 1, 2, 3 are correct
B. 1, 3, 5, are correct
C. 1, 2, 4, are correct
D. 1, 2, are correct
E. 1, 2, 3, 5, are correct

Answer 1

Hint: Remember that the part of a muscle where the area which lies between the two Z lines is generally known as a sarcomere. Try to find the correct statement that appears least in the options. Also contraction and relaxation is done by the protein components of sarcomere.

Complete answer:
The sliding action theory of muscle contraction will help in solving this question. The sliding action theory suggests that the myosin filaments are responsible for holding the actin filaments and when there is a signal of contraction or relaxation the actin filaments are responsible for it. The actin filaments are arranged in a linear fashion horizontally to the muscle and the myosin filaments occur at certain intervals doing the job of holding the actin filaments. when there is contraction the actin filaments are stretched out making a lot of space and the myosin filaments stay at their places but because of the contraction they come near to their other nearest filaments and thus providing us with the dark bands. When the actin filaments are stretched out they give light bands in their place.
The sliding action theory suggests that it is the actin filaments which contracts or expands instead of the myosin filaments and it is the myosin filaments which do the job of holding the expanded filaments of actin to their place.
Now if we consider the last statement which says that the central part of thin filaments not overlapped by thick filaments is the H line but it is wrong in place that it is the part where the central part of the thick filaments is not overlapped by the thin filaments.
And the fourth statement which is the definition of the sarcomere is correct.

Therefore, Option (C) is correct.

Additional Information: there exists other different types of lines like the M line and the I line in the sarcomere but they are not discussed much because of their less significance. Also the muscle contraction is an energy dependent process.

Note:
The part between the thin filaments which is not overlapped by the thick filaments of a muscle is known as the Z line and it is the end part of the sarcomere and the H line is the midpoint of a sarcomere.