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describe the important step of muscle contraction?

Muscles are one of the contractile organs of our body. They are the fleshy parts of our body, which help in the movement of different body parts. Muscles move by contracting and relaxing. Here, contracting means becoming shorter, while relaxing means becoming longer and thinner. If we make a fist with one hand and bend the arm at the elbow level.

We will feel a swollen region inside your upper arm. This swollen region is a muscle. Contraction makes it swollen.

When we bring our arm back to its normal position, you will observe that the muscle is no longer contracted. When muscles contract, they become shorter, thicker, and stiffer.

Functioning of muscles

Muscles work in pairs to pull a bone. If one muscle contracts, then its partner (the other muscle of the pair) relaxes. This pulls the bone towards the contracted muscle.

Can you tell how muscles come back to their original position?

When the relaxed muscles contract and the contracted muscles relax, muscles are pulled back to their original position.

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During skeletal muscle contraction, the thick filament slides over the thin filament by a repeated binding and releases myosin along the filament. This whole process occurs in a sequential manner.
 

Step 1:

Muscle contraction is initiated by signals that travel along the axon and reach the neuromuscular junction or motor end plate. Neuromuscular junction is a junction between a neuron and the sarcolemma of the muscle fibre. As a result, Acetylcholine (a neurotransmitter) is released into the synaptic cleft by generating an action potential in sarcolemma.
 

Step 2:

The generation of this action potential releases calcium ions from the sarcoplasmic reticulum in the sarcoplasm.
 

Step 3:

The increased calcium ions in the sarcoplasm leads to the activation of actin sites. Calcium ions bind to the troponin on actin filaments and remove the tropomyosin, wrapped around actin filaments. Hence, active actin sites are exposed and this allows myosin heads to attach to this site.
 

Step 4:

In this stage, the myosin head attaches to the exposed site of actin and forms cross bridges by utilizing energy from ATP hydrolysis. The actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.
 

Step 5:

After muscle contraction, the myosin head pulls the actin filament and releases ADP along with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are broken.
 

Step 6:

This process of formation and breaking down of cross bridges continues until there is a drop in the stimulus, which causes an increase in calcium. As a result, the concentration of calcium ions decreases, thereby masking the actin filaments and leading to muscle relaxation.

cHeErS!! :)

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