Final answer:
The conduction velocity within cardiac myocytes is determined by ionic movements across cell membranes, with calcium ions playing a significant role in both the contraction process and the propagation of electrical impulses through the heart's conduction system.
Step-by-step explanation:
The conduction velocity within cardiac myocytes is determined by several factors, including the movement of ions such as sodium (Na+), potassium (K+), and calcium (Ca2+) across their membranes. The conduction system of the heart, comprising the sinoatrial node, internodal pathways, atrioventricular node, bundle of His, bundle branches, and Purkinje fibers, coordinates this process. Calcium ions are particularly critical; their influx through slow calcium channels facilitates the prolonged plateau phase in cardiac contractile cells, which ensures an adequate refractory period and efficient heart contraction. The balance between the influx of Ca2+ during the plateau phase and the Ca2+ released from the sarcoplasmic reticulum is essential for contraction. The conduction velocity is fastest in the Purkinje fibers, which allows quick and synchronized transmission of the electrical impulse to the ventricular muscle cells, leading to a well-coordinated contraction from the apex towards the base of the heart.