The sudden death of Rev John Smith, the charismatic preacher, shocked many people, he had just finished preaching when he suddenly collapsed in the pulpit. The postmortem results showed that he had died of Cardiomyopathy, a condition associated with sudden cardiac arrest .
There has been a lot of debate about what causes cardiomyopathy. Some experts have argued that it occurs as a result of interruption in nervous stimulation due to psychological problems, yet others have refuted the claims urging that the heart muscles are self-excitable and cannot be stimulated by the nervous system. All reasons presented may be valid but it should be understood from a scientific point of view that the cardiac muscle is myogenic (contraction is initiated by the cell itself, not an outside occurrence or stimulus such as nerve innervation), and therefore it operates independent of any nervous stimulation.
Those supporting the concept that nervous stimuli contribute to cardiomypathy have based their argument on the anatomical structure of the heart which shows it to have branches of autonomic nervous system . When this nerve endings are stimulated, they argue, they increase or decrease heart beat respectively .Indeed , some experiments have successfully demonstrate that cardiac arrest can be resuscitated through stimulation of the nervous system. This ,according to them is a direct indication that the nervous system is involved in the beating of the heart. These claims may have been exaggerated because presence of nervous system, does not mean it is the one that controls contraction and relaxation of cardiac fiber . Experiments have showed that the cardiac muscle can continue to function even without the presence of the nervous system and that even a strong nervous stimulation cannot resuscitate a cardiac muscle that has completely stopped functioning . The nervous system can only modify the rate at which the heart beats.
The Sinoatrium node (SAN), an autonomous pacemaker found on the walls of the heart, is the one that initiates the intrinsic ability of the cardiac fibers to contract and relax .Experiments have shown that this region has no connection with the nervous system in any way. This is to say that the heart muscle is myogenic in nature it functions automatically. This means that the contraction process is initiated in the pacemaker region of the heart and it spreads over the heart from one cell to another because cells are electrically coupled to one another via membrane junctions. The nature and extent of coupling determines the pattern by which the electrical waves of excitation spread over the cardiac muscle and also influences the rate of conduction.
Written by DOMINIC KIPKOECH MAGUT
1 Valary C Stanlon and Tina Sanders, Essentials of Anatomy and Physiology, F.A Davis Company; Philadelphia –Fourth edition. 2007
2 Eckert and Randall , Animal physiology; Mechanism and Adaptation, Second edition.
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Photo: (U.S. Air Force photo by SSgt. DERRICK C. GOODE)(RELEASED)