Skeletal and cardiac muscle cells store calcium in extensive networks of smooth ER.
Cardiac muscles are those that build up the heart. These muscles have the ability of auto-rhythmicity. Thus means that they can perform movements on their own. Cardiac muscles are also called involuntary muscles, because they do not move according to the wish of the individual.
Smooth ER is the one that does not have ribosomes attached on its surface. It acts as a reservoir for storing the calcium ions inside the cell. These calcium ions are transported to the cell organelle by active transport and release by the signals of hormones.
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