artery lecture 1

Myocardium and Heart Regulation

• The medulla oblongata serves as the control center for heart rate regulation.

• There are two main types of nerve pathways involved:

  • Sympathetic Nerves:

    • Increase heart rate and strength of contractions.

    • Originate from the medulla oblongata.

  • Vagus Nerve:

    • Part of the parasympathetic nervous system.

    • Decreases heart rate by primarily affecting the SA node.

Role of Nerves in Heart Function

• The vagus nerve slows down the SA node, which in turn decreases the heart rate of the entire system.

• The cardiac sympathetic nerves have a broader effect:

  • Influence the SA node, AV bundle, AV branches, and ventricles.

Heart Cycle Overview

• The heart cycle refers to the sequence of events during each heartbeat, which includes:

  • Contraction (Systole): When the ventricles contract, pushing blood out.

  • Relaxation (Diastole): When ventricles relax, allowing them to fill with blood.

• Each heartbeat encompasses one complete cycle of contraction and relaxation.

• Always viewed from the perspective of the ventricles:

  • When ventricles are in systole, atria are in diastole and vice versa.

Phases of the Heart Cycle

• Phases during Systole and Diastole:

  • Total Systole: All phases of ventricular contraction.

  • Atrial Systole: Atria contract, pushing blood into ventricles.

  • Early Ventricular Systole: Ventricles begin to contract.

  • Late Ventricular Systole: Ventricles fully contract.

  • Early Ventricular Diastole: Ventricles start to relax.

  • Total Diastole: Myocardium is completely relaxed; no blood can be held.

• During total diastole, blood passively fills the heart chambers.

Valve Operations During Heart Cycles

• AV Valves: Open during ventricular diastole, allowing blood from the atria to fill the ventricles.

• Semilunar Valves: Closed during ventricular diastole, preventing backflow of blood from the aorta and pulmonary artery into the ventricles.