Final answer:
The normal firing of the Bundle of His/Purkinje Fibers is from the a)atria to the ventricles, corresponding to when the heart contracts during systole after an impulse from the SA node.
Step-by-step explanation:
The normal firing of the Bundle of His/Purkinje Fibers is from the atria to the ventricles, which is indicated by option a. The heart contracts to pump blood through the body during systole and is filled with blood during diastole.
An electrical charge spontaneously pulses from the SA node causing the two atria to contract. The pulse reaches the AV node where it pauses before spreading to the walls of the ventricles. It enters the Bundle of His, then to the left and right bundle branches extending through the interventricular septum. The Purkinje fibers conduct the impulse from the apex up the ventricular myocardium, causing the ventricles to contract. This pause allows the atria to empty their contents into the ventricles before the ventricles pump out the blood.