What is depolarization in the context of cardiac cycles?

What is depolarization in the context of cardiac cycles?

• A. The relaxation of the ventricles
• B. The phase of muscle contraction
• C. The closing of heart valves
• D. The starting phase of blood flow

Answer: (B)

Depolarization in the context of cardiac cycles refers to the phase where the cardiac muscle cells undergo a change in electrical charge, leading to muscle contraction. This process is initiated by the movement of sodium ions into the cardiac cells, resulting in a shift in the membrane potential that allows the heart muscle to contract. During depolarization, electrical impulses trigger the heart to pump blood effectively. In the heart, this typically occurs just before the ventricles contract, marking a crucial part of the cardiac cycle where the heart fills with blood and then ejects it into the circulatory system. Understanding depolarization is essential for interpreting EKG readings, as it corresponds to the QRS complex, which represents ventricular depolarization. The other contexts provided do not accurately describe depolarization. Relaxation of the ventricles occurs during diastole, after contraction. The closing of heart valves is part of the cardiac cycle related to pressure changes inside the chambers, but it does not reflect depolarization itself. The starting phase of blood flow refers to the beginning of the cardiac cycle but does not directly relate to the electrical events that trigger contraction.

Depolarization in the context of cardiac cycles refers to the phase where the cardiac muscle cells undergo a change in electrical charge, leading to muscle contraction. This process is initiated by the movement of sodium ions into the cardiac cells, resulting in a shift in the membrane potential that allows the heart muscle to contract.

During depolarization, electrical impulses trigger the heart to pump blood effectively. In the heart, this typically occurs just before the ventricles contract, marking a crucial part of the cardiac cycle where the heart fills with blood and then ejects it into the circulatory system. Understanding depolarization is essential for interpreting EKG readings, as it corresponds to the QRS complex, which represents ventricular depolarization.

The other contexts provided do not accurately describe depolarization. Relaxation of the ventricles occurs during diastole, after contraction. The closing of heart valves is part of the cardiac cycle related to pressure changes inside the chambers, but it does not reflect depolarization itself. The starting phase of blood flow refers to the beginning of the cardiac cycle but does not directly relate to the electrical events that trigger contraction.