AV Node and Bundle: Heart Conduction — NEET Biology

Correct answer: C — S2, S4 and S6 only

The question focuses on the intrinsic regulation and conduction system of the heart, testing for incorrect statements based on NCERT content. S1: This statement is correct. The NCERT says, "The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable." (Page 199, Para 3) S2: This statement is NOT correct. The SA node is located in the *right upper corner* of the right atrium, not the lower left. The NCERT states, "A patch of this tissue is present in the right upper corner of the right atrium called the sino-atrial node (SAN)." (Page 199, Para 3) S3: This statement is correct. The NCERT describes, "A bundle of nodal fibres, atrio-ventricular bundle (AV bundle) continues from the AVN which passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum and immediately divides into a right and left bundle." (Page 199, Para 3) S4: This statement is NOT correct. Purkinje fibres distribute throughout the *ventricular* musculature, not the atrial musculature. The NCERT says, "These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called purkinje fibres." (Page 199, Para 3) S5: This statement is correct. The NCERT states, "The SAN can generate the maximum number of action potentials, i.e., 70-75 min–1, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the pacemaker." (Page 199, Para 3) S6: This statement is NOT correct. A healthy individual's heart normally beats 70-75 times per minute (average 72), not approximately 100 times. The NCERT mentions, "Our heart normally beats 70-75 times in a minute (average 72 beats min–1)." (Page 199, Para 3) Therefore, statements S2, S4, and S6 are NOT correct.