I am not sure, but i think they empty into the chambers.
Both atria open and close simultaneously.
the atriventriculart node causes both atria to contract
Those are the veins that drain blood from the lungs, and empty into the left atria.
They both contract at the same time.
The Sinoatrial Node sends a wave of electric impulses through the heart, which causes both atria to contract.
Nodal or pacemaker cells.
Contraction of both atria
SA node sends an impulse for the atria to contract. AV node is then activated which contracts the ventricles.
the atria
The are extentions of the Atria.
both the right and left atria receive blood.
The atria are a part of your heart which is in the circulatory system