Final answer:
The branches of the bundle branches that help contract the ventricles are known as Purkinje fibers, which are specialized myocardial conduction fibers responsible for the fast and coordinated spread of electrical impulses in the ventricle walls.
Step-by-step explanation:
The branches of the bundle branches that transmit the impulses to the walls of the ventricles, causing the ventricles to contract, are called Purkinje fibers. These are specialized myocardial conduction fibers that arise from the bundle branches and are responsible for spreading the impulse to the myocardial contraction fibers of the ventricles. This process starts with a signal from the sinoatrial node causing the atria to contract. The pulse then reaches the atrioventricular node where it pauses. Afterward, it travels through the atrioventricular bundle, on to the left and right bundle branches, and finally reaches the Purkinje fibers which facilitate the contraction of the ventricles.