Question

Is an action potential required to initiate smooth muscle contraction?
1) True
2) False

Answer 1

Contrary to skeletal muscle, smooth muscle contraction is initiated by the influx of extracellular calcium ions rather than an action potential.

Step-by-step explanation:

False, an action potential is not required to initiate smooth muscle contraction. In smooth muscle fibers, calcium ions (Ca2+) play a crucial role in triggering contraction. These fibers have a much smaller diameter compared to skeletal muscle cells, which means T-tubules are not required to transmit an action potential deep into the fiber for contraction to occur. Instead, smooth muscle cells have calcium channels in the sarcolemma that open during an action potential along the sarcolemma. The influx of extracellular Ca2+ ions, which diffuse into the sarcoplasm and reach the calmodulin, is predominantly responsible for initiating contraction in a smooth muscle cell.