Anatomy 101 by Kevin Langford

Author:Kevin Langford [Langford, Kevin]
Language: eng
Format: epub
Publisher: Adams Media, Inc.

HEART REGULATION

With Every Beat of Your Heart

A unique feature of the heart is that it beats spontaneously and rhythmically on its own. Regardless of any nervous system signals, the heart starts beating before you are born and consistently and continually beats until your death.

Pacemaker and Conduction

Setting the beat for the heart is the task of the pacemaker tissue in the right atrium. Much like a metronome continues to click once started, the pacemaker, once generated, beats for a lifetime. Beginning as tissue in the embryonic sinus venosus, a primitive and embryonic chamber receiving blood from the body, it becomes incorporated into the right atrial wall as development proceeds. The pacemaker is named the sinoatrial node (SA node) to represent its embryonic origins and its final adult location.

Cells of the sinoatrial node are modified cardiac muscle connected to the muscle cells of the atrium via the gap junctions of the intercalated disks. (Gap junctions allow direct cell-to-cell contact; intercalated disks are features of cardiac muscle that allow for contraction.) When the cells of the SA node spontaneously generate an action potential, it spreads to all the cells of both atria through these junctions.

The muscles of the atria and the muscles of the ventricles are separated by a connective tissue ring called the annulus fibrosus that forms the foundational anchor for the valves and the septa of the heart, which prevent the SA node signal from spontaneously spreading to the ventricles. Additional conductive cells pick up and relay the electrical signal through the annulus downward to the ventricles.

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