In skeletal muscle Catt is essential for the contraction process. For skeletal
muscle cells, what is the source of Cat+.?

The source of Calcium (Ca⁺⁺) for the skeletal muscle cells is the sarcoplasmic reticulum, the main store of intracellular Ca⁺⁺.

Explanation:

Calcium (Ca⁺⁺) is an ion that plays an important role in muscle contraction, a process that requires high cytoplasmic concentrations of this ion to promote myofibrillary activity.

The sarcoplasmic reticulum (SR) -equivalent to the endoplasmic smooth reticulum- is an organelle that regulates the contractile activity of skeletal muscle. The two terminal cisterns of the SR attach to the T-tube, forming a triad, which surrounds the myofibrilla.

Once the muscle cell receives the signal to contract, the Ca⁺⁺ channels are opened and allow Ca⁺⁺ to enter the cell, promoting the exit of this cation from the SR and increased its cytoplasmic levels. This stimulates muscle contraction.

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