Why is the concentration of calcium so high in the sarcoplasmic reticulum during rest?

Explanation:

The sarcoplasmic reticulum is a system found within muscle cells and involved in the storage of intracellular calcium, this function is crucial for the cells because calcium is used to trigger the muscle contraction through excitation and depolarization of the cell, shifting the membrane potential.

Since the presence of too much calcium in the cells leads to calcification (hardening of structures), the sarcoplasmic reticulum is also an important way to control the calcium ion levels in the cell absorbing it from the cell to go back to rest.

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answer; i believe the correct answer is (replication is not conservative);

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.