Question

One heartbeat in an average man lasts
A) 0.8 sec
B) 0.2 sec
C) 0.5 sec
D) 1 min

Answer 1

Heart beat is the rhythmic contraction and expansion of heart. Actually, contraction and expansion occur separately in atria and ventricles. However, ventricular movements are quite prominent and forceful. One heart beat is represented by one cardiac cycle.

Complete answer:
Contraction of heart is called Systole while relaxation is called Diastole.
The sequence of events in a single heartbeat is known as Cardiac cycle. This cycle involves systole and diastole of the atria and ventricles.
Initially all the four chambers of the heart are in a relaxed state . This is called Joint Diastole stage. In this stage, the bicuspid and tricuspid valves are open which allow the flow of blood from pulmonary vein and vena cava to left and right atrium respectively.
When SA nodes send out an electric signal, then atrial systole is stimulated . During this period, atrium undergoes continuous contraction which forcefully passes the blood into the ventricles through tricuspid and bicuspid valves. When ventricles are filled with blood, ventricular systole begins. AV node picks up the signal and then conducts it throughout the ventricular. This stimulates the further ventricular contraction, this causes the closure of AV valves and opening of the semilunar valve . through this blood flow into the pulmonary artery and the aorta .
This closure of AV valve results in production of the first heart sound ‘lub’ During ventricular diastole , the ventricles relax , arterial pressure falls and blood begins to flow back to the ventricles . This reversal of pressure causes the semilunar valve to close, producing a second sound of heart ‘dub’.
One heartbeat represents one cardiac cycle which lasts for 0.8 sec.

Hence the correct answer is OPTION(A)

Note: Heart beat is entirely controlled by nervous supply in arthropods and some annelids. It is called neurogenic heart. While in molluscs and vertebrates heart beat originates from a special muscular tissue . Such a heart is called Myogenic heart . Human heart is myogenic.