Final answer:
The Purkinje fibers are specialized conduction fibers that spread the electrical impulse to the ventricles' contractile cells, causing their contraction. They begin at the apex of the heart and ensure a coordinated contraction towards the base, critical for efficient blood pumping.
Step-by-step explanation:
The Purkinje fibers are specialized myocardial conduction fibers that arise from the atrioventricular bundle branches. These fibers are crucial for the propagation of the electrical impulse that leads to the contraction of the ventricles.
They spread the impulse to the myocardial contractile cells within the ventricles, ensuring that the contraction is coordinated and efficient.
The electrical stimulation provided by the Purkinje fibers starts at the apex of the heart and travels toward the base, facilitating an upward squeeze of blood out of the ventricles to the aorta and pulmonary trunk. The time from the initiation of the impulse in the SA node until the depolarization of the ventricles is approximately 225 ms.