Answer:
- The sarcomere is relaxed.
- Calcium ions are released by a nerve cell.
- Actin and myosin are activated.
- The sarcomere shortens.
- Actin and myosin overlap completely.
Explanation:
For muscle contraction to occur it is necessary that the brain first sends signals to motor neurons that will quickly establish contact with muscle fibers.
At that time, the axons close to the muscle fibers will lose the myelin sheath, as a result of which, the axons will dilate forming a kind of plaque called the motor plaque. The main function of this motor plate is to allow the motor nerves to connect to the muscles.
Simultaneously, the nervous impulse will reach the aconic terminations of the motor nerves. This will cause the release of acetylcholine over the muscle fibers causing an action potential to occur. After that, the actin and misin filaments contract, as a result the sarcomere becomes decreased and as it decreases it causes muscle contraction.
In summary, muscle contraction happens as follows:
- The sarcomere is relaxed.
- Calcium ions are released by a nerve cell.
- Actin and myosin are activated.
- The sarcomere shortens.
- Actin and myosin overlap completely.
