Cardiac Nodal Tissue
இதய முனைய திசு
The heart does not wait for the brain to tell it to beat. It is myogenic, driven by specialized nodal tissue. If you think the nervous system initiates the heartbeat, you are already losing marks.
The idea
Cardiac nodal tissue consists of the Sino-atrial node (SAN) and the Atrio-ventricular node (AVN). The SAN is located in the right upper corner of the right atrium, while the AVN is in the lower left corner of the right atrium close to the atrio-ventricular septum. These tissues are auto-excitable, generating action potentials without external stimuli. They form the basis of the heart's conduction system, ensuring rhythmic contraction.
Why it matters
It provides the heart with myogenic properties, allowing it to initiate and regulate its own rhythmic contractions independently.
NEET lens
NEET focuses on the exact anatomical location of SAN and AVN. Remember: SAN is the 'pacemaker' and AVN is the 'pace-setter'. Questions often swap their locations or functions to trap you. Memorize the sequence: SAN -> AVN -> Bundle of His -> Purkinje fibers.
Clinical significance
Failure of the SAN to generate impulses leads to 'Sick Sinus Syndrome,' causing bradycardia or syncope. When the conduction pathway between the nodes is blocked, a 'Heart Block' occurs, requiring an artificial pacemaker. The heart's rhythm is a matter of electrical precision; even a millisecond delay is pathological.
Introduction
Cardiac nodal tissue consists of specialized myocardial cells that generate and conduct electrical impulses automatically (autorhythmicity), controlling the heartbeat rhythm without requiring nervous system input.
Core concept
Nodal tissue components: SA Node (Sinoatrial node) — 'pacemaker', right atrium, generates impulse at 70-75 bpm. AV Node (Atrioventricular node) — junction of atria and ventricles, delays impulse (~0.1 sec) to allow atria to empty before ventricles contract. Bundle of His — in interventricular septum. Right and Left bundle branches. Purkinje fibres — spread impulse to ventricular myocardium. Properties: Autorhythmicity (self-excitable), conductivity (fast signal propagation). SA node is the natural pacemaker — fastest spontaneous rate, overrides all lower centres.
Go deeper
Why the AV node delay matters: if impulse reached ventricles simultaneously with atria, both would contract at the same time → atrial blood wouldn't have time to fill ventricles → inefficient pumping. The 0.1 sec AV delay ensures atrial contraction completes before ventricular systole begins.
From Class 10
Your heart beats automatically without you thinking about it. Special muscle cells that generate electrical signals on their own — not nerves — control this rhythm. These are cardiac nodal tissue.