ANATOMY

GENERAL ANATOMY

ANATOMY OF THE HEART

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Which of the following pacemaker cells of the heart normally determines heart rate?
A
atrial conducting fibers
B
SA node
C
Ventricular myocardial cells
D
AV node
Explanation: 

Detailed explanation-1: -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 pacemaker of the heart.

Detailed explanation-2: -The cells of the SA node at the top of the heart are known as the pacemaker of the heart because the rate at which these cells send out electrical signals determines the rate at which the entire heart beats (heart rate).

Detailed explanation-3: -Pacemaker cells are highly specialized myocardial cells whose intrinsic ability to rhythmically depolarise and initiate an action potential is responsible for the basal heart rate.

Detailed explanation-4: -ventricular foci normally have an intrinsic rate 20-40bpm.

Detailed explanation-5: -We can see how phase 0 of pacemaker cells differs from atrial/ventricular myocytes. Depolarization of atrial/ventricular myocytes is a result of sodium ions entering the cell (“summit”), whereas depolarization of pacemaker cells is the result of calcium ions entering the cell (“climb”).

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