MICROANATOMY

Detailed explanation-1: -The heart rate can vary quite remarkably depending on various environmental and physiologic factors. At rest, the SA nodal myocytes depolarize at an intrinsic rate between 60 and 100 beats per minute, which is generally considered a normal heart rate.

Detailed explanation-2: -The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The atria are then activated. The electrical stimulus travels down through the conduction pathways and causes the heart’s ventricles to contract and pump out blood.

Detailed explanation-3: -The SA node is considered the pacemaker of the heart. Its electrical signals normally cause the atria of an adult’s heart to contract at a rate of about 60 to 100 times a minute.

Detailed explanation-4: -Systole is the contraction phase of the cardiac cycle, and diastole is the relaxation phase. At a normal heart rate, one cardiac cycle lasts for 0.8 second.