Question

multiple choice question
cardiac muscle contraction is similar to contraction in skeletal muscle except that in cardiac muscle, calcium ___.
binds to actin instead of to troponin
binds to calmodulin initiating muscle contraction
comes from outside the cell as well as the sarcoplasmic reticulum

Explanation:

In cardiac muscle, calcium ions enter the cell from the extracellular fluid through voltage - gated calcium channels in addition to being released from the sarcoplasmic reticulum. In skeletal muscle, calcium mainly comes from the sarcoplasmic reticulum. Calcium binds to troponin in both skeletal and cardiac muscle (not actin), and in smooth muscle (not cardiac or skeletal), calcium binds to calmodulin to initiate contraction.

Answer:

O comes from outside the cell as well as the sarcoplasmic reticulum