The heart muscle does not require external stimulation to contract, but the autonomic nervous system exerts a considerable influence on the latter.
The control centers of the cardiac autonomic nervous system located in the medulla oblongata: the cardio accelerator center plans neuronal extensions even neurons segments T1 -> T5 spinal cord, which synapse with postganglionic neurons of cervical lymph and upper chest, from where they are nerve fibers synapse with sinus and atrioventricular nodes.
The cardiovascular center inhibitor, it has the nerve fibers which leave the medulla oblongata to the heart via the nerve X.

The phenomena of electrical stimulation:
The cells are pacemakers in the sinus node, the atrioventricular node and atrioventricular bundle (bundle of His). The sinus node is located in the wall of the right atrium. It is the primary pacemaker center: typically, the sinus node depolarizes spontaneously 70 times per minute, and mark the pace of all contractile cells.



This characteristic rhythm is called sinus rhythm and determines the basal heart rate.
The sinus node, the action potential (AP) propagates through the atria, where he borrows the internodal tract of the heart connecting the sinoatrial node to the atrioventricular node. (time: 0.04 s). At this node, the impulse is delayed by 0.1 s, allowing the atria complete their contraction. Then, the PA traverses the atrioventricular bundle, located in the interventricular septum, which ends in Purkinje fibers (also called cardiac conduction myofibres). The latter enter the apex and back into the walls to cause ventricular contraction. (T 0.22 s on average a healthy heart).


In case of failure of the sinus node, the atrioventricular node sets the rhythm at 40-60 beats per minute: this is called r ythme nodal rhythm.

Electrocardiogram:
To record the ECG, using 12-lead standard that provide a comprehensive picture of cardiac activity. Typically, it consists of 5 types of waves:

  • The P wave of low amplitude due to depolarization of the atria, caused by the sinus node and has a duration of approximately 0.08 s.
  • The QRS complex formed waves Q, R, S is related to the ventricular depolarization and a period of 0.08 s. The atrial repolarization is hidden
  • T wave is caused by ventricular repolarization duration of 0.16 s.