A) SA-node
B) Ventricles
C) Purkinje fibres
D) AV-node
Correct Answer: A
Solution :
The stimulus for contraction of the heart originates in a specific region of the right atrium called Sinu Atrial-node (SA-node) or pace maker, which spreads waves of contraction across the walls of the atria via muscle fibres at regular intervals. When these wave of contraction reaches Atrio Ventricular-node (AV-node) or pace setter the latter is stimulated and excitatory impulses are rapidly transmitted from it to all parts of ventricle via bundle of His and Purkinjes fibres. These impulses stimulate the ventricle to contract simultaneously. The ventricles force blood through long system of arteries and hence, must exert great pressure on the blood.
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