Why are the heart tissues/ cells structured the way they are?
The myocardium is composed of specialized cardiac muscle cells with an ability not possessed by muscle tissue elsewhere in the body. Cardiac muscle, like other muscles, can contract, but it can also carry an action potential (i.e. conduct electricity), like the neurons that constitute nerves. Furthermore, some of the cells have the ability to generate an action potential, known as cardiac muscle automaticity. The blood supply of the myocardium is carried by the coronary arteries. The myocardium is subject to two opposed electrical subsets of control. First order electrical control of the myocardium is derived from the sinoatrial node. Propagation of first order control from the sinoatrial node is closely tied to sympathetic discharge. Second order electrical control of the myocardium is closely tied to parasympathetic influence from the spinal vertebral ganglia and vagus nerves.
