Question

Which is correct about the contraction sequence of the heart?

Select one:

a. The right atrium and ventricle contract at the same time, and as they are relaxing, the left atrium and left ventricle begin to contract.

b. The two atria contract at the same time, and as they are relaxing, the two ventricles contract together.

c. Contraction begins in the order: right atrium, then right ventricle, then left atrium, then left ventricle.

d. The atria and ventricles begin their contractions at the exact same time, but the atrial contraction only lasts half as long as the ventricle contraction.

e.  The contraction and relaxation of all four chambers happen at the same time.

Answer is NOT A

Answer 1

The two atria contract at the same time, and as they are relaxing, the two ventricles contract together.

SA node generates impulses first and spreads to the walls of the atria which makes the two atria to contract first at the same time, later the impulse moves to the AV node.

from AV node to Purkinje fibers through the bundle of his to muscles of ventricles. while the atria relax the ventricles start contracting.