Question

process of muscle contraction

Answer 1

An action potential in a motor neuron causes acetylcholine to release in the synaptic cleft.Acetylcholine binds with receptors on the cell membrane on the muscle fiber, opening Ca2+ -Na+ channels. Usually referred to as Calcium channels.
Calcium is released from the terminal cisternae into the muscle fiber.
Calcium binds to troponinTroponin shifts tropomyosin, which was blocking the active site on the actin.
Myosin heads attach to actin by breaking down ATP to ADP and a phosphate via Myosin-ATPaseThe Myosin head forms a ‘cross-bridge’ on the active site of the actin filament.
The cross bridge pulls actin, which slides over the myosin – known as the ‘Power Stroke.’
The release of ADP completes the cross-bridge movement and ATP attaches to myosin, breaking the actin-myosin crossbridge.
Every time ATP is split into ADP + P, the myosin head ‘cocks’ into place to form another cross bridge with actin.
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Answer 2

Heya!

Here is your answer!
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During skeletal muscle contraction, the thick filament slides over the thin filament by a repeated binding and releases of myosin head 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.As a result, the concentration of calcium ions decreases, thereby masking the actin filaments and leading to muscle relaxation.

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