Question

Which of the following is correct about the given figure

a. The length of the thick and thin myofilaments has changed.
b. Length of both anisotropic and isotropic bands has changed.
c. The myosin cross-bridges move on the surface of actin and the thin and thick myofilaments slide past each other.
d. Length of the sarcomere remains the same.

Answer 1

Muscles have unique properties such as excitability, Elasticity, extensibility, and Contraction. These are of three types- Cardiac, Skeletal, and Smooth muscles. Actin and myosin are a part of skeletal muscle and are present in Sarcolemma.

Complete answer:
In the above diagram, it is clearly visible that the myosin cross-bridges move on the surface of actin and thin and the thick myofilaments slide past each other.

This is a diagram of a muscle fiber that is a part of skeletal muscle. The detailed anatomy shows three main parts-
• Sarcolemma- It is an external layer of muscle fiber that gives proper shape to skeletal muscle.
• T tubules or transverse tubules- Sarcolemma undergoes invaginations to form channels or tubules.
• Sarcoplasm- Cytoplasm of the sarcolemma. It contains myofibrils that participate directly in muscle contraction. Within myofibrils, special proteins are formed which are called Myofilaments which further contains two more important proteins-
• Actin- It is responsible for the formation of thin filaments and Myosin which are responsible for the formation of thick filaments. Together both of them form a compartment-like structure called Sarcomere. So, in the above diagram, we can see two sarcomeres which are maximally contracted.
When myosin heads move over actin proteins, contraction takes place.

Hence, the correct answer is option (C).

Note: Important observations when muscle tissue is constricted:
- The isotropic bands represent light bands(only thin filaments).
- The length of thick and thin myofilaments also remains the same.
- The length of both anisotropic and isotropic bands remains the same.
- The length of the Sarcomere also does not remain the same.
- The skeletal muscle cell contains anisotropic and isotropic bands.
- The anisotropic bands represent the darker bands- I band(both thick and thin filaments) and A band an(only thick filaments).