52. A normal heartbeat begins with spontaneous electrical activity that coordinates atrial and ventricular contraction. Which of the following describes the correct physiological sequence of electrical conduction in the human heart?
(A) signals from the sinoatrial (SA) node spreading through atria → signals delayed in the atrioventricular (AV) node → bundle branches passing signals to the heart apex → signals spreading upward throughout ventricles via Purkinje fibers.
(B) signals from the atrioventricular (AV) node spreading through atria → signals delayed in the sinoatrial (SA) node → bundle branches passing signals to the heart apex → signals spreading upward throughout ventricles via Purkinje fibers.
(C) signals from the sinoatrial (SA) node spreading through ventricles → signals delayed in the atrioventricular (AV) node → bundle branches passing signals to the heart apex → signals spreading upward throughout atria via Purkinje fibers.
(D) signals from the sinoatrial (SA) node spreading through atria → bundle branches passing signals to the heart apex → signals delayed in the atrioventricular (AV) node → signals spreading upward throughout ventricles via Purkinje fibers.
(E) signals from the atrioventricular (AV) node spreading through atria → bundle branches passing signals to the heart apex → signals delayed in the sinoatrial (SA) node → signals spreading upward throughout ventricles via Purkinje fibers.