7.3. Structure of the Heart
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The heart is arranged into four chambers: two atria (singular = atrium) and two ventricles. There is a left and right atrium and a left and right ventricle. The interatrial septum divides the left and right atria. The interventricular septum divides the left and right ventricles. The atrioventricular septum divides the two atria and the two ventricles.
The right side of the heart pumps blood to the lungs via the pulmonary circulation, while the left side of the heart pumps blood to the tissues and organs of the body via the systemic circulation.
The heart is a muscle. It is composed of cardiac muscle. It is also myogenic, i.e. it generates its own electrical signals. The functions of the sympathetic and parasympathetic divisions of the nervous system are only to influence the rate of this myogenic electrical signal and the force of the contractions that they generate. The autonomic nervous system can increase or decrease the heart rate and force of contraction, but it does not generate the original electrical signal.