Cardiac conduction system
Cardiac conduction system: The electrical conduction system that controls the heart rate. This system generates electrical impulses and conducts them throughout the muscle of the heart, stimulating the heart to contract and pump blood.
Among the major elements in the cardiac conduction system are the sinus node, atrioventricular node, and the autonomic nervous system.
The sinus node is the heart’s natural pacemaker. The sinus node is a cluster of cells situated in the upper part of the wall of the right atrium. The electrical impulses are generated there. (The sinus node is also called the sinoatrial node.)
The electrical signal generated by the sinus node moves from cell to cell down through the heart until it reaches the atrioventricular node (the AV node), a cluster of cells situated in the center of the heart between the atria and ventricles.
The AV node serves as a gate that slows the electrical current before the signal is permitted to pass down through to the ventricles. This delay ensures that the atria have a chance to fully contract before the ventricles are stimulated. After passing the AV node, the electrical current travels to the ventricles along special fibers embedded in the walls of the lower part of the heart.
The autonomic nervous system (the same part of the nervous system as controls the blood pressure) controls the firing of the sinus node to trigger the start of the cardiac cycle. The autonomic nervous system can transmit a message quickly to the sinus node so it in turn can increase the heart rate to twice normal within only 3 to 5 seconds. This quick response is important during exercise when the heart has to increase its beating speed to keep up with the body’s increased demand for oxygen.
Read Also:
- Cardiac defibrillator, implantable
Cardiac defibrillator, implantable: A device that is designed to be put in the body to recognize certain types of abnormal heart rhythms (arrhythmias) and correct them by delivering precisely calibrated and timed electrical shocks to restore a normal heartbeat. Defibrillators continuously monitor the heart rhythm in order to detect overly rapid life-threatening arrhythmias, such as […]
- Cardiac index
Cardiac index: A cardiodynamic measure based on the cardiac output, which is the amount of blood the left ventricle ejects into the systemic circulation in one minute, measured in liters per minute (l/min). Cardiac output is indexed to a patient’s body size by dividing by the body surface area to yield the cardiac index.
- Cardiac myocyte
Cardiac myocyte: A heart muscle cell. Sometimes called a myocyte when it is understood that it is in the heart. See also: Myocyte.
- Cardiac muscle
Cardiac muscle: A type of muscle tissue that is found only in the heart and is distinguishable from the two other forms of muscle, smooth muscle (that moves internal organs, such as the bowels, and vessels, such as the artery walls) and skeletal muscle (that powers joints). Cardiac muscle is responsible for pumping blood throughout […]
- Cardiac myxoma
Cardiac myxoma: A benign tumor of the heart and the most common type of heart tumor in adults. Cardiac myxomas can appear in an isolated case or in families, sometimes as part of an hereditary syndrome called the Carney complex. Some families have the Carney complex variant as well as the trismus-pseudocamptodactyly syndrome (Hecht syndrome). […]