What is the function of the Purkinje fibers?contract atria bottom upcontract ventricles bottom upcontract atria top downcontract ventricles top down

The function of the Purkinje fibers is to contract the ventricles from the bottom up. These fibers are part of the heart's electrical system and they ensure that the ventricles contract in a coordinated manner, pushing blood out of the heart. Here are the steps of how it works:

1. The electrical signal for a heartbeat originates in the sinoatrial (SA) node, also known as the natural pacemaker of the heart. This signal causes the atria (the top chambers of the heart) to contract.

2. The signal then travels to the atrioventricular (AV) node, which acts as a kind of relay station, slowing down the signal before it moves on to the ventricles (the bottom chambers of the heart).

3. From the AV node, the signal travels down the bundle of His (a pathway of specialized cells), which divides into two bundle branches along the interventricular septum (the wall that separates the two ventricles).

4. The bundle branches then connect to the Purkinje fibers, which spread the signal throughout the ventricles, causing them to contract from the bottom up. This pushes the blood out of the heart, either to the lungs (from the right ventricle) or to the rest of the body (from the left ventricle).

So, the correct answer to your question is "contract ventricles bottom up".