Heart Function and Electrical Activity

Heart Anatomy and Function

  • The heart is classified as a muscle functioning continuously, likened to a pump.

Electrical Activity of the Heart

  • Each heartbeat is initiated by an electrical signal generated from within the heart muscle.
  • This electrical activity can be recorded by an electrocardiogram (EKG/ECG).

Sinoatrial Node (SA Node)

  • The heartbeat begins with the electrical signal from the sinoatrial node (SA node).
  • Location: The SA node is situated in the right atrium of the heart.

Blood Flow and Atrial Contraction

  • When the right atrium is filled with blood:
    • The electrical signal spreads across the cells of both the right and left atria.
    • This causes the atria to contract, which pumps blood through the open valves into both ventricles.
  • The contraction of the atria is represented by the P wave on the EKG.

Atrioventricular Node (AV Node)

  • The electrical signal reaches the atrioventricular node (AV node), located near the ventricles:
    • Here, the signal is briefly slowed down to allow both ventricles to fill with blood.
  • On the EKG, this delay is indicated by the line segment between the P wave and the Q wave.

Bundle of His and Bundle Branches

  • After the AV node, the signal is transmitted to the bundle of His within the heart's ventricles:
    • The bundle of His splits into left and right bundle branches running through the septum of the heart.
  • The propagation of the signal through the bundle branches is indicated by the Q wave on the EKG.

Purkinje Fibers and Ventricular Contraction

  • The signal travels from the bundle branches to the Purkinje fibers, which connect directly to the ventricular walls.
  • The electrical signal spreads rapidly across the walls of the ventricles, causing:
    • Both ventricles to contract, but not simultaneously:
    • The left ventricle contracts slightly before the right ventricle.
  • The contraction of the left ventricle is marked by the R wave on the EKG,
  • The contraction of the right ventricle is marked by the S wave on the EKG:
    • Right Ventricle: Contracts and pushes blood through the pulmonary valve to the lungs.
    • Left Ventricle: Contracts and pushes blood through the aortic valve to the rest of the body.

Ventricular Relaxation

  • After contraction, the walls of the ventricles relax and await the next electrical signal:
  • This relaxation is indicated by the T wave on the EKG, marking the period when the ventricles are preparing for the next contraction.

Continuous Cycle

  • This sequence of events - contraction and relaxation - is a repetitive cycle, continuing throughout the life of the heart.