Sinus node

Sinus node

The sinus node or sinoatrial node (SA node) is a group of cells located in the superior part of the right atrium of the heart. These cells have the ability to spontaneously produce an electrical impulse, which travels through the heart, causing it to contract and pump blood. This makes the sinus node the natural pacemaker of the heart.

Structure

The sinus node is a crescent-shaped structure that measures about 15 mm in length and 5 mm in width. It is located in the superior part of the right atrium, near the opening of the superior vena cava. The cells of the sinus node are smaller than other heart cells and have few myofibrils, which gives them their unique pacemaking ability.

Function

The primary function of the sinus node is to generate electrical impulses that regulate the heart's rhythm. This process is known as automaticity. The rate at which the sinus node produces these impulses is influenced by signals from the nervous system and by levels of certain hormones in the body.

Clinical significance

Problems with the sinus node can lead to a variety of arrhythmias, or abnormal heart rhythms. For example, if the sinus node produces impulses at an abnormally slow rate, it can result in a condition called sinus bradycardia. On the other hand, if the sinus node produces impulses at an abnormally fast rate, it can lead to a condition called sinus tachycardia.

See also

• Heart
• Cardiac conduction system
• Electrocardiogram

References

Sinus node Resources
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