Question

The strongest common denominator among smooth, skeletal, and cardiac muscle contraction is their shared dependence on Ca++ for the initiation of contraction. Cardiac and skeletal muscles exhibit several characteristics not shared by smooth muscle. For example, the contractile proteins in both cardiac and skeletal muscles are organized into discrete sarcomeres. Both muscle types also possess some semblance of a T tubule system and are dependent on the generation of action potentials for their contraction. Smooth muscle, in contrast, is relatively less organized, is uniquely regulated by myosin light chain phosphorylation, and can contract in vivo in the absence of action potentials. What is the strongest common denominator among smooth, skeletal, and cardiac muscle contraction?

1) Dependence on Ca++ for the initiation of contraction
2) Organization of contractile proteins into discrete sarcomeres
3) Possession of a T tubule system
4)ependence on the generation of action potentials for contraction

Answer 1

The common denominator among smooth, skeletal, and cardiac muscle contraction is their reliance on calcium ions to initiate contraction, despite their differences in structure and contraction regulation.

Step-by-step explanation:

The strongest common denominator among smooth, skeletal, and cardiac muscle contraction is their dependence on Ca++ for the initiation of contraction. This is because, despite the differences in structure and regulation among these types of muscle, the influx of calcium ions is critical to start the contraction process in each one. In skeletal muscle, this process is primarily triggered by action potentials delivered via motor neurons, while in cardiac muscle, calcium ions enter from extracellular spaces and the sarcoplasmic reticulum to initiate contraction. Smooth muscle also relies on calcium ions, which come from both extracellular sources and their sarcoplasmic reticulum; however, they are uniquely regulated by the phosphorylation of myosin light chains and can contract without action potentials. Therefore, the correct answer is 1) Dependence on Ca++ for the initiation of contraction.