sinussolmukkeen

The sinoatrial node, often abbreviated as the SA node, is a specialized area of cardiac tissue located in the upper wall of the right atrium of the heart. It is a critical component of the heart's electrical conduction system, functioning as the heart's natural pacemaker. The SA node is composed of modified cardiac muscle cells that possess the unique ability to spontaneously generate electrical impulses. These impulses are initiated at a regular rate, which dictates the heart's rhythm and rate of contraction. The electrical signal generated by the SA node then spreads outward through the atria, causing them to contract and pump blood into the ventricles. Following atrial contraction, the impulse reaches the atrioventricular node (AV node), which delays the signal briefly before transmitting it to the ventricles, causing them to contract and pump blood out to the rest of the body. The intrinsic rate of the SA node is typically between 60 to 100 beats per minute at rest, though this rate can be modulated by the autonomic nervous system. Hormonal influences and various physiological states can also affect the SA node's firing rate. When the SA node malfunctions, it can lead to abnormal heart rhythms such as bradycardia (a slow heart rate) or tachycardia (a fast heart rate), or even more complex arrhythmias. Medical conditions affecting the SA node are collectively referred to as sick sinus syndrome.