Sinoatrial node


A specialized bundle of neurons in the upper right atrium that acts as the heart’s natural pacemaker.

Fires at a rate of 60-70 beats per minute in a healthy an resting heart.

Its electrical impulse triggers electrical events that control the orderly sequence of heart muscle contractions.

The sinoatrial node is a group of pacemaker cells which spontaneously depolarize to create an action potential. 


This cardiac action potential then spreads across both atria causing them to contract, forcing the blood they hold into their corresponding ventricles.

The depolarization and repolarization of the SA node activity can be measured as voltage changes on an electrocardiogram.

The node undergoes self-firing with depolarization and repolarization with input of body oxygen demand and other physiological factors which control the rate of SA node firing and therefore heart rate.

It is located at the point where the superior vena cava meets the right atrium.

Contains two types of cells; small pacemaker cells and elongated cell that conduct impulses.

The electrical impulse form the SA node goes to the right and left atria and causes contraction and forces blood to the ventricles.

Related to the P wave on the electrocardiogram and does not directly affect contraction of the ventricles.

It is under the direct control of the autonomic nervous system, with inhibition by the parasympathetic nervous system and enhancement by the sympathetic nervous system.

Increased heart rate can result from decreased parasympathetic activity and an increased rate from increased sympathetic activity.

Stimulation of the vagus nerve slows down or can even momentarily stop the firing of the SA node.

Its firing effects the firing of the AV node.

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