[Plate 221, Innervation of Heart: Schema]Both divisions of the autonomic nervous system provide fibers to the cardiac plexus
The conducting system of the heart coordinates the cardiac cycle of contraction. It consists of
The sinoatrial node (SA node), located at the superior end of the sulcus terminalis of the right atrium, near the entrance of the
superior vena cava
The SA node is the so-called pacemaker of the heart, from which impulses for contraction are initiated and spread through the
musculature of both atria.
Fibers from the cardiac plexus supply the SA node.
Sympathetic innervation accelerates the rate and force of contraction of heart muscle.
Parasympathetic stimulation slows down the rate and force of contraction of heart muscle.
Signal from the SA node is propagated by the cardiac muscle to the AV node.
The AV node is located near the inferior end of the interatrial septum posteriorly, near the septal cusp of the tricuspid valve.
The AV bundle carries the signal from the AV node through the fibrous skeleton of the heart and the membranous interventricular septum.
It divides into right and left bundles that pass on either side of the muscular interventricular septum.
The fibers of the right and left bundles (Purkinje fibers) spread into the walls and papillary muscles of the ventricles.
Purkinje fibers from the right bundle innervate the anterior papillary muscle of the right ventricle via the septomarginal trabecula or
moderator band, to coordinate the timing of the contraction of the papillary muscles.Heart Sounds
Clinicians need to listen to valve sounds.
Blood carries sound in the direction of its flow, so valve sounds are best heard (auscultated) directly superficial to their location or at the end
of a line of blood flow through the valve.