Question

Define sliding filament theory of muscle contraction

Answer 1

Hint: Muscle is a contractile tissue that is a differentiating characteristic of animals. Muscle contraction is the process of activation of tension generating sites within a muscle fibre. When muscle cells are viewed, they contain a striped pattern which is formed by a series of basic units called sarcomere.

Complete step by step answer:
In the year 1954, scientists published two papers that described the molecular basis of muscle contraction. They described the position of actin and myosin filaments at different stages of muscle contraction fibres.
H.E. Huxley, A.F. Huxley and J. Hanson with the help of high-resolution microscopy observed the changes in the sarcomeres as muscle tissue shortened.
They observed that one zone of sarcomere arrangement i.e. “A band” remained constant in length during muscle contraction.
The A band contains myosin that are thick filaments which remained constant in length while other sarcomere shortened.
The scientists noticed that “I band” that contains actin (thin filaments) changes in length along with the sarcomere during the contraction of the muscle fibres.
All these observations led them to sliding filament theory of muscle contraction.
Sliding filament theory states that sliding of actin past myosin generates muscle tension. Because actin is tied up to the structure that is located at the lateral ends of each sarcomere known as z discs or z bands.
Any shortening of thin filament i.e. actin would lead to shortening of sarcomere and thus, the muscle.

Note:
Muscle contraction provides great flexibility to the animals. Sarcomere are the basic unit that controls the changes in muscle length. Scientists proposed sliding filament theory of muscle contraction to explain the mechanisms of molecules behind muscle contraction.