Question

Define sliding filament theory of muscles contraction. Explain the important steps of it.

Answer 1

Hint: Muscle contraction in the muscle fibers is responsible for activating the tension-generating sites. Muscle contraction requires a signal from the nervous system. The signal is generated in the form of action potential and is transmitted as an impulse through a motor neuron.

Complete answer:
A single sarcomere consists of several parallelly occurring filaments referred to as actin filaments, which are the thin filaments and myosin, which are the thick filaments. The contraction of muscles occurring inside the body is based on the sliding filament theory. It involves generation of tension in a muscle through repetitive events which involves the sliding of thin actin filament over a thick myosin filament.
When the impulse reaches at the neuromuscular junction, sarcoplasmic reticulum is stimulated to discharge the calcium ions. These calcium ions in turn bind to the troponin thereby eradicating the tropomyosin which was attached at the myosin binding site present on the actin.
Now the cross bridge can be formed between the myosin and actin. The ATP is converted into ADP, Pi and energy with the help of enzyme ATPase existing on the head of myosin.
The head of the myosin then binds with the action which slides over one other allowing the shortening of muscles. After this, with the end of stimulation, removal of calcium ions takes place returning the muscle back to normal state.

Note: Muscle shortening is not necessary in conditions of contraction of muscle. The tension in muscles can be generated with no alteration in its length. This can be observed while holding a heavy object at static position.