When receives stimulation from SA node, AV node signals ventricles to contract by way of Purkinje fibers . Implantation of artificial pacemaker provides regular 0.85 second stimulus. Records ionic changes that occur with contraction of heart muscle. P wave represents excitation prior to contraction of the atria. QRS wave occurs prior to ventricular contraction.
T wave shows repolarization of ventricles causing recovery of the ventricles.
Uncoordinated contraction of ventricles. Can be caused by injury or drug overdose. Ventricles must be defibrillated by applying strong electric current allowing SA node to reestablish coordinated beat. Extrinsic Control a. Cardiac center in medulla oblongata can alter heartbeat through autonomic nervous system. Parasympathetic system promotes normal responses including slowing down heartbeat.