The following is a list of the events that occur during a muscle contraction.
1. myosin cross-bridges bind to the actin.
2. the free myosin head splits atp.
3. calcium ion is released from the sarcoplasmic reticulum.
4. the myosin head pivots toward the center of the sarcomere.
5. calcium ion binds to troponin.
6. the myosin head binds an atp molecule and detaches from the actin.

the correct sequence of these events is
-1, 4, 6, 2, 3, 5.
-3, 5, 1, 4, 6, 2.
-3, 5, 1, 2, 4, 6.
-1, 3, 5, 4, 6, 2.
-5, 1, 4, 6, 2, 3.

The answer is 3,5,1,4,6,2

Explanation: A muscle contraction is an increase in the tension (force exerted by the muscle on a bone) or a decrease in the length of a muscle. The steps that occurs during muscle contraction are:

1. Depolarization of the T-tubules causes release of calcium from the lateral sacs of the sarcoplasmic reticulum.

2. Calcium binds to the troponin-tropomyosin complex in the actin filaments,releasing the inhibition that prevented actin from combining with myosin.

3. Myosin head attaches to the exposed site of actin and forms cross bridges by utilizing energy from ATP hydrolysis. It is at this stage that the contraction of the muscle occurs .

4. ATP binds to the myosin cross-bridge, breaking the actin-myosin bond and allowing the cross-bridge to dissociate from actin.

5. Cross-bridge activation continues as long as the concentration of calcium remains high enough to inhibit the action of the troponin-tropomyosin system.

When stimulation ceases, calcium moves back into the lateral sacs of the sarcoplasmic reticulum .

6. Removal of calcium restores the inhibitory action of

troponin-tropomyosin. In the presence of ATP, actin and myosin remain in the dissociated, relaxed state.

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