Body Fluids and Circulation Question 49
49. All the components of the nodal tissue are autoexcitable. Why does the SA node act as the normal pacemaker?
[2019]
(a) $SA$ node has the highest rate of depolarisation.
(b) SA node has the lowest rate of depolarisation.
(c) SA node is the only component to generate the threshold potential.
(d) Only SA node can convey the action potential to the other components.
Show Answer
Answer : a
Hints & Solutions
(a) SA node acts as pace-maker of heart because its autoexcitable tissue have the ability to generates heart impulses at highest rate (frequency). This electrical impulse is then transmitted by perinodal cells, or transitional $(T)$ cells, to the right atrium and then through the rest of the heart’s electrical conduction system, eventually resulting in myocardial contraction and blood distributed to the rest of the body. The sinus node continuously generates electrical impulses, thereby setting the normal rhythm and rate in a healthy heart. Hence, the SA node is referred to as the natural or normal pacemaker of the heart.
