Biology · Body Fluids and Circulation · NEET
It is MUSCLE, not nerve. NCERT calls it 'a specialised cardiac musculature called the nodal tissue.' Because the beat starts inside this muscle and not from any nerve, the heart is said to be myogenic. This is a very common NEET trap: nodal tissue is modified cardiac muscle, so it can contract and also generate its own action potential (autoexcitable).
SAN (sino-atrial node) is a patch of nodal tissue in the RIGHT UPPER corner of the RIGHT atrium. AVN (atrio-ventricular node) is another mass in the LOWER LEFT corner of the RIGHT atrium, close to the atrio-ventricular septum. Note both are in the right atrium. Students often wrongly place the AVN in the left atrium; it is in the right atrium near the septum.
AVN (atrio-ventricular node) is the node that receives the signal from the SAN and briefly delays it. The AV bundle (bundle of His) is the conducting cable that continues FROM the AVN, passes through the atrio-ventricular septum, and then divides into the right and left bundle branches. So AVN = the node; AV bundle = the tract leaving that node.
Purkinje fibres are the final, finely branched part of the nodal tissue spread throughout the walls of the ventricles. The bundle branches carry the impulse down to the heart apex, and there they continue as Purkinje fibres, which quickly spread the signal to the whole ventricular muscle so both ventricles contract together and pump blood out.
The short AVN delay lets atrial contraction (atrial systole) finish first, so the atria empty their blood completely into the ventricles before the ventricles begin to contract. This timing gap makes pumping efficient. A NEET 2019 question tested exactly this: the delay allows 'the atria to empty completely.'
SAN → AVN → AV bundle (bundle of His) → right and left bundle branches → Purkinje fibres → ventricular muscle. NEET 2024 asked this order and the answer was E-C-A-D-B (SA node, AV node, AV bundle, bundle branches, Purkinje fibres). Learn this exact order.
A specialised nodal tissue embedded in the lower corner of the right atrium, close to Atrio-ventricular septum, delays the spreading of impulses to heart apex for about 0.1 sec. The delay allows:
Following are the stages of pathway for conduction of an action potential through the heart: A. AV bundle B. Purkinje fibres C. AV node D. Bundle branches E. SA node. Choose the correct sequence of pathway.
Which one of the following statements is correct?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because the beat is auto-regulated by specialised muscle (the nodal tissue), not by any nerve. The signal is made inside the heart muscle itself, so the heart is myogenic. A frog's heart even keeps beating for a while after it is removed from the body.
About 70-75 per minute. This is the highest rate among all nodal parts, which is why the SAN sets the pace and is called the pacemaker (giving a resting heart rate of around 72 beats/min).
The bundle of His is the atrio-ventricular bundle (AV bundle). It continues from the AVN, passes through the atrio-ventricular septum, and then splits into the right and left bundle branches that carry the impulse toward the ventricles.
Yes. All components of the nodal tissue can generate their own action potentials (autoexcitable). But the SAN depolarises fastest, so it dominates and the others follow its rhythm.
