Organ
Sinoatrial node
The usual starting point of each heartbeat
High-yield
Locate the sinus node near the upper crista terminalis, beneath the outer surface of the right atrium.
Overview
A small region of specialized myocardium near the superior caval–right atrial junction normally initiates atrial excitation. Its cells depolarize spontaneously and communicate with surrounding atrial muscle. Autonomic input adjusts their activity as the body's demands change.
Reference facts
- Location
- Near the superior vena cava–right atrial junction, mainly subepicardial at the upper terminal groove
- Parts
- Pacemaker myocardium with transitional connections to atrial muscle
- Blood supply
- A sinus nodal artery, most often arising from the right coronary or circumflex artery
- Innervation
- Vagal cardiac input slows pacemaker activity; sympathetic input accelerates it
- Relations
- Beside the superior caval opening and upper crista terminalis
- Function
- Normally initiates the rhythm that activates the atria and then reaches the AV conduction system
Clinical correlation
Sinus node dysfunction can produce inappropriate slowing, pauses or an inadequate rate increase with activity; fast atrial rhythms may alternate with slow periods. Both intrinsic tissue disease and external influences can contribute.
Frequently asked questions
Where is the sinoatrial node located?
The sinoatrial node lies near the superior vena cava–right atrial junction, mainly subepicardial at the upper terminal groove.
What does the sinoatrial node do?
Normally initiates the rhythm that activates the atria and then reaches the AV conduction system.
What are the parts of the sinoatrial node?
The parts of the sinoatrial node are the pacemaker myocardium with transitional connections to atrial muscle.
What is the blood supply of the sinoatrial node?
A sinus nodal artery, most often arising from the right coronary or circumflex artery.