Sinoatrial node
|
WikiDoc Resources for Sinoatrial node |
|
Articles |
|---|
|
Most recent articles on Sinoatrial node Most cited articles on Sinoatrial node |
|
Media |
|
Powerpoint slides on Sinoatrial node |
|
Evidence Based Medicine |
|
Clinical Trials |
|
Ongoing Trials on Sinoatrial node at Clinical Trials.gov Trial results on Sinoatrial node Clinical Trials on Sinoatrial node at Google
|
|
Guidelines / Policies / Govt |
|
US National Guidelines Clearinghouse on Sinoatrial node NICE Guidance on Sinoatrial node
|
|
Books |
|
News |
|
Commentary |
|
Definitions |
|
Patient Resources / Community |
|
Patient resources on Sinoatrial node Discussion groups on Sinoatrial node Patient Handouts on Sinoatrial node Directions to Hospitals Treating Sinoatrial node Risk calculators and risk factors for Sinoatrial node
|
|
Healthcare Provider Resources |
|
Causes & Risk Factors for Sinoatrial node |
|
Continuing Medical Education (CME) |
|
International |
|
|
|
Business |
|
Experimental / Informatics |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
The sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are modified cardiac myocytes. They possess some contractile filaments, though they do not contract.
Role as a pacemaker
Although all of the heart's cells possess the ability to generate the electrical impulses (or action potentials) that trigger cardiac contraction, the sinoatrial node is what normally initiates it, simply because it generates impulses slightly faster than the other areas with pacemaker potential. Because cardiac myocytes, like all muscle cells, have refractory periods following contraction during which additional contractions cannot be triggered, their pacemaker potential is overridden by the sinoatrial node.
Cells in the SA node will naturally discharge (create action potentials) at about 60-100 times/minute.[1] Because the sinoatrial node is responsible for the rest of the heart's electrical activity, it is sometimes called the primary pacemaker.
If the SA node does not function, or the impulse generated in the SA node is blocked before it travels down the electrical conduction system, a group of cells further down the heart will become the heart's pacemaker. These cells form the atrioventricular node (AV node), which is an area between the atria and ventricles, within the atrial septum.
Innervation
The SA node is richly innervated by parasympathetic nervous system fibers (CN X: Vagus Nerve) and by sympathetic nervous system fibers (T1-4, Spinal Nerves). This makes the SA node susceptible to autonomic influences.
- Stimulation of the vagus nerve (parasympathetic fibers) causes a decrease in the SA node rate (thereby decreasing the heart rate and force of contraction).
- Stimulation via sympathetic fibers causes an increase in the SA node rate (thereby increasing the heart rate and force of contraction).
Blood supply
In the majority of patients, the SA node receives blood from the right coronary artery.