Calcium's Role in Smooth Muscle

The video explains excitation-contraction coupling in smooth muscles, focusing on calcium's role. Calcium enters the cell from extracellular fluid and sarcoplasmic reticulum, triggering contraction by binding with calmodulin and activating myosin light chain kinase. This leads to phosphorylation of myosin, enabling the cross-bridge cycle and muscle contraction. Relaxation occurs when calcium is pumped out, deactivating the kinase and stopping the cycle. The process is summarized, highlighting calcium's central role.

What is the primary role of calcium ions in smooth muscle contraction?

• To provide energy for contraction

• To increase the temperature of the muscle

• To facilitate the contraction process

• To decrease the muscle's pH

Which of the following is the main source of calcium for smooth muscle contraction?

• Mitochondria

• Extracellular fluid

• Nucleus

• Golgi apparatus

What structure in smooth muscle cells contains calcium channels that open upon action potential?

• Mitochondria

• Nucleus

• Caveolae

• Golgi apparatus

What protein does calcium bind to inside the smooth muscle cell to initiate contraction?

• Myosin

• Actin

• Calmodulin

• Troponin

Which enzyme is activated by the calcium-calmodulin complex?

• Myosin light chain kinase

• Myosin light chain phosphatase

• ATP synthase

• Phospholipase C

What happens to the myosin light chain during muscle contraction?

• It is dephosphorylated

• It is converted to actin

• It is phosphorylated

• It is broken down

What is the role of myosin phosphatase in muscle relaxation?

• It adds phosphate to the myosin light chain

• It removes phosphate from the myosin light chain

• It binds calcium ions

• It activates calmodulin

How is calcium removed from the cytoplasm to facilitate muscle relaxation?

• Through calcium channels

• By calcium pumps on the cell membrane and sarcoplasmic reticulum

• By diffusion into the nucleus

• By binding to actin

What happens to the ATPase activity of myosin when the regulatory light chain is dephosphorylated?

• It decreases

• It remains unchanged

• It converts to GTPase activity

• It increases

Which of the following summarizes the source of calcium for smooth muscle contraction?

• From the mitochondria

• Only from the extracellular fluid

• Only from the sarcoplasmic reticulum

• From both extracellular fluid and sarcoplasmic reticulum