Question

In the context of vascular smooth muscle, what is the correct sequence of events during contraction and relaxation?

a) Contraction: Calcium influx, phosphorylation of myosin light chains, cross-bridge formation; Relaxation: Calcium removal, dephosphorylation of myosin light chains, cross-bridge detachment

b) Contraction: Calcium removal, dephosphorylation of myosin light chains, cross-bridge detachment; Relaxation: Calcium influx, phosphorylation of myosin light chains, cross-bridge formation

c) Contraction: Calcium influx, dephosphorylation of myosin light chains, cross-bridge detachment; Relaxation: Calcium removal, phosphorylation of myosin light chains, cross-bridge formation

d) Contraction: Calcium influx, phosphorylation of myosin light chains, cross-bridge formation; Relaxation: Calcium influx, dephosphorylation of myosin light chains, cross-bridge detachment

Answer 1

Smooth muscle contraction is initiated by calcium influx and phosphorylation of myosin light chains, resulting in cross-bridge formation and muscle contraction. Relaxation occurs when calcium is removed and myosin light chains are dephosphorylated, causing cross-bridge detachment and muscle relaxation.

Step-by-step explanation:

Smooth muscle contraction is regulated by calcium ions and the phosphorylation of myosin light chains. During contraction, calcium influx triggers the phosphorylation of myosin light chains by myosin (light chain) kinase, allowing for cross-bridge formation between actin and myosin. The cross-bridge then pulls on the thin filaments, resulting in muscle contraction.

During relaxation, calcium is removed from the cytosol, leading to the dephosphorylation of myosin light chains by phosphatase. This causes the cross-bridge to detach from actin and the muscle to relax.