The AV valve is open and the semilunar valve is closed during ventricular diastole.
diastole
Ventricle diastole is the period during which the ventricles are relaxing. During ventricular diastole, the pressure in the (left and right) ventricles drops from the peak that it reaches in systole. When the pressure in the left ventricle drops to below the pressure in the left atrium, the mitral(bicuspid) valve opens, causing accumulated blood from the atrium to flow into the ventricles.
The semi-lunar valves
yes
diastolic blood pressure
gao
Because not all of the blood that is in the heart, which was brought in during diastole, is ejected during systole. There is some back flow of blood, which can't make it over the aortic arch because of lack of pressure, into the heart.
When the ventricular pressure exceeds the pressure in the aorta and pulmonary trunk, the semilunar valves are forced open and blood is ejected out. This signals the ejection phase of the cardiac cycle of ventricular systole.
In late diastole (relaxation phase), the semilunar (pocket) valves close, due to decreasing arterial pressure, to prevent blood flowing back into the ventricles. These stay closed during atrial systole. (But open again during ventricular systole.)Then, as the ventricles contract during ventricular systole, the bicuspid and tricuspid valves close to prevent blood from flowing back to the atria.So, it really depends on which phase of the contraction we are looking at.(Ed: format)
The two semilunar valves are the aortic valve and the pulmonic valve. The aortic valve opens when the left ventricle contracts, allowing blood to pass into the aorta. The pulmonic valve opens when the right ventricle contracts, allowing blood to pass into the pulmonary artery.
During the T-wave the ventricles are repolarizing, preparing for the next beat.
do not require an external stimulus to reach threshold, while other cardiac cells do.