Body Fluids And Circulation

The human heart is myogenic, meaning the impulse for contraction arises within the cardiac muscle itself. NCERT Class 11, Chapter 18 (Body Fluids and Circulation) explains that a specialised mass of neuromuscular tissue, the sinoatrial node (SAN), is located in the upper right corner of the right atrium and generates the fastest spontaneous impulses, setting the heart rhythm. Because it discharges most frequently, the SAN is called the pacemaker. The atrioventricular node sits near the atrioventricular septum and relays the impulse from atria to ventricles, but its intrinsic rate is slower, so it does not normally set the pace. The bundle of His conducts the impulse from the AV node into the ventricular septum and is purely a conducting pathway. Purkinje fibres distribute the impulse through the ventricular walls, triggering coordinated ventricular contraction, again without initiating the beat. Thus the sinoatrial node is correct. A functional plausibility check confirms it: the pacemaker must be the tissue with the highest intrinsic firing frequency, and among the listed components only the SAN holds that role in a healthy heart.