ANATOMY

Detailed explanation-1: -The main role of a sinoatrial node cell is to initiate action potentials of the heart that can pass through cardiac muscle cells and cause contraction. An action potential is a rapid change in membrane potential, produced by the movement of charged atoms (ions).

Detailed explanation-2: -SA nodal action potentials are divided into three phases. Phase 4 is the spontaneous depolarization (pacemaker potential) that triggers the action potential once the membrane potential reaches threshold between-40 and-30 mV).

Detailed explanation-3: -The cardiac action potential originates from the sinus node, located high in the right atrium (Fig. 9-1). Its cells depolarize spontaneously and initiate the spontaneous depolarization of action potentials at a regular rate from the sinus node.

Detailed explanation-4: -The right vagus nerve primarily innervates the SA node. The left vagus primarily innervates the atrial–ventricular (AV) node.

Detailed explanation-5: -Sinoatrial (SA) node normally generates the action potential, i.e. the electrical impulse that initiates contraction. The SA node excites the right atrium (RA), travels through Bachmann’s bundle to excite left atrium (LA). The impulse travels through internodal pathways in RA to the atrioventricular (AV) node.