The human heart beats approximately 72 times a minute, which is more than a hundred thousand times in a day. With each heart beat it pumps around 70ml of oxygen-rich blood into the body, and an equal amount of oxygen-poor blood into the lung. The muscles of the heart are designed to push the blood into the body with enough force to deliver the vital elixir of life to all parts of the body, including the brain—overcoming gravity and the resistance offered by the often hardened blood vessels. It is almost a miracle that this bag of muscle—the heart— performs the function for the entire life, while consuming only seven per cent of all the energy utilised by the body.
Controlling this amazing organ is the heart’s own nervous system—a specialised network of cells that have similarity to the brain cells (neurons). The specialised tissue in the heart is organised into nodes and conducts tracts that generate electrical signals for the muscle cells of the heart. The muscle pump function requires all the muscle cells to act at nearly the same time to generate the pumping force with great efficiency.
The heart’s conduction system can activate all heart muscle cells in less than 100 milliseconds (one-tenth of a second), and it controls how fast or slow the heart beats. As you can imagine, abnormalities in the conduction system— a heart rhythm disorder—can affect the blood flow to vital organs and cause various symptoms or even sudden death.
Sometimes there is abnormal neural control of the heart. A specialist will suspect this when an elderly person has a sudden loss of consciousness. After the checks, we would slightly massage his carotid arteries in the neck while monitoring his ECG and we would be able to detect a sudden pause in his heart activity.
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