APPLIED RADIOLOGICAL ANATOMY

Detailed explanation-1: -The sinus node continuously generates electrical impulses, thereby setting the normal rhythm and rate in a healthy heart. Hence, the SA node is referred to as the natural pacemaker of the heart.

Detailed explanation-2: -The parasympathetic nerves supplying the SA node (in particular the Vagus nerves) originate in the brain. These nerves release a neurotransmitter called acetylcholine (ACh). ACh binds to a receptor called an M2 muscarinic receptor, located on the SA node membrane.

Detailed explanation-3: -The SA node starts the sequence by causing the atrial muscles to contract. That’s why doctors sometimes call it the anatomical pacemaker. Next, the signal travels to the AV node, through the bundle of HIS, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract.

Detailed explanation-4: -The origin of the heartbeat in the sino-atrial (SA) node is usually thought to arise from the sequential activation of a variety of ionic currents in pacemaker cells (Irisawa et al. 1993). Recently, the possibility has been considered that heart rate might be influenced by transient changes in cytosolic Ca2+.