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Question
Sino-atrial node is called the pacemaker of our heart. Why?
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Solution
- The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, there by controlling the sequence of muscle contractions that pumps blood out of the heart.
- Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.
- Its fibres have a resting potential of 55 to 60 millivolts, whereas in cardiac muscles it is 85 to 95 millivolts and in the specific conducting fibres spread in the heart it is 90 to 100 millivolts. The heart beat starts due to the leakage of sodium ions from the inferior vena cava (SAN).
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