Question

In the heart, action potentials spread across the ______ of cardiac muscle cells, causing them to contract.

Answer 1

In the heart, action potentials spread across the sarcolemma of cardiac muscle cells, causing them to contract.

Sarcolemma

A muscle cell's cell membrane is known as the myolemma, or sarcolemma (Greek for "flesh" and "lemma," or "sheath"). It comprises of a thin polysaccharide layer that touches the basement membrane and a lipid bilayer. Numerous tiny collagen fibrils and specific proteins, including laminin, are present in the basement membrane and act as a scaffold on which the muscle fiber can attach. The actin skeleton within the cell is linked to the basement membrane and the cell's surface by transmembrane proteins in the plasma membrane. The surface layer of the sarcolemma fuses with a tendon fiber at each end of the muscle fiber, and the tendon fibers then aggregate into bundles to produce the muscle tendons that attach to bones.

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