The motor neuron carries the nerve impulse.
↓
The nerve impulse reaches the neuromuscular junction.
↓
Calcium ions release into the myofibrils.
↓
Myosin and actin protein filaments attach to each other.
↓
Myosin filaments pull on the actin filaments.
↓
The sarcomere shortens.
The neurotransmitter (ACh) from motor neurons signals a muscle fiber to depolarize. The depolarization (Na+) will trigger Ca++ release and will initiate contraction by binding to troponin. Myosin pulls the actin strands. ATP sustains the contraction.
When myosin filaments pull actin filaments closer together and thus shortens the sarcomeres within a fiber. When all the sarcomeres in a muscle fiber shorten, the muscle fiber contracts.
Muscle contraction refers to the tightening, shortening, and lengthening of muscles while performing any activity or task.
The steps of muscle fiber contraction in correct order are:
1). The motor neurons carry the nerve impulse.
2). The nerve impulse reaches the neuromuscular junction.
3). Calcium ions release into the myofibrils.
4). Myosin and actin protein filaments attach to each other.
5). Myosin filaments pull on the actin filaments.
6). The sarcomere shortens.
During muscle fiber contraction, the neurotransmitter Acetylcholine leads to the depolarization of muscle fiber, this results in the release of Calcium ions that binds to protein troponin. Myosin filaments pull on the actin filaments, and finally muscle fiber contracts.
Therefore, when myosin filaments pull actin filaments closer together and thus shortens the sarcomeres within a fiber. When all the sarcomeres in a muscle fiber shorten, the muscle fiber contracts.
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