Describe the origin and conduction of a cardiac impulse.

The origin of a cardiac impulse begins in the sinoatrial (SA) node, located in the right atrium of the heart. The SA node is known as the "pacemaker" of the heart because it generates electrical impulses that set the rhythm of the heart. These impulses spread through the atria, causing them to contract and push blood into the ventricles.

From the SA node, the electrical impulse travels to the atrioventricular (AV) node, located between the atria and ventricles. The AV node delays the impulse slightly to allow the atria to fully contract before the impulse is conducted to the ventricles.

After passing through the AV node, the impulse travels down the bundle of His, a collection of specialized muscle fibers that conduct the impulse to the Purkinje fibers. The Purkinje fibers then distribute the impulse throughout the ventricles, causing them to contract and pump blood out of the heart.

This coordinated sequence of electrical impulses and muscle contractions ensures that the heart beats in a regular and efficient manner, allowing it to effectively pump blood throughout the body.