3D CONTENT
3D HEART ANATOMY

MYOCARDIUM AND CONDUCTING SYSTEM

Author: Dr. Bogdan Leahu
Myocardium anatomy 360-degree interactive viewer showing thick muscular layer of heart wall, ventricular wall thickness variation, and vortex of heart at cardiac apex
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Myocardium - Cardiac Muscle Layer, Preview from the app.

TABLE OF CONTENTS

MYOCARDIUM

  • Thick muscular layer of the heart wall
  • Responsible for contractile function
  • Composed primarily of cardiac muscle cells

Thickness Variation

  • Thinner in atria
  • Significantly thicker in ventricles
  • Left ventricle thickest due to systemic pressure demands
  • Right ventricle thinner as it pumps to pulmonary circulation

Vortex of the Heart

  • Located at cardiac apex
  • Where both ventricles meet
  • Muscle fibres twist and spiral
  • Arrangement promotes efficient contraction

CONDUCTING SYSTEM OF THE HEART

Cardiac conducting system 360-degree viewer showing SA node, AV node, bundle of His, bundle branches, and Purkinje fibres embedded within myocardium
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Conducting System Overview, Preview from the app.

  • Specialised network embedded within myocardium
  • Generates and transmits electrical impulses
  • Ensures coordinated cardiac muscle contraction
  • Regulates heartbeat and maintains rhythm

Components

  • Sinoatrial node
  • Atrioventricular node
  • Atrioventricular bundle
  • Bundle branches
  • Purkinje fibres

SINOATRIAL NODE

Sinoatrial node 360-degree viewer showing tadpole-shaped SA node in right atrium near superior vena cava opening within terminal groove
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Sinoatrial Node (SA Node), Preview from the app.

  • Natural pacemaker of the heart
  • Tadpole-shaped structure
  • Generates electrical impulses
  • Impulses spread throughout atria first

Location

  • Right atrium
  • Near superior vena cava opening
  • Within terminal groove

ATRIOVENTRICULAR NODE

Atrioventricular node 360-degree viewer showing AV node within Triangle of Koch in right atrium near interatrial septum
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Atrioventricular Node (AV Node), Preview from the app.

  • Specialised cluster of cells
  • Functions as critical gateway
  • Briefly delays impulse transmission
  • Delay allows atria to fully contract
  • Ensures atrial blood empties into ventricles before ventricular contraction

Location

  • Right atrium near septum
  • Within Triangle of Koch

ATRIOVENTRICULAR BUNDLE

Atrioventricular bundle 360-degree viewer showing Bundle of His penetrating fibrous skeleton connecting atria and ventricles electrically
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Atrioventricular Bundle (Bundle of His), Preview from the app.

  • Also known as Bundle of His
  • Composed of specialised conducting fibres
  • Penetrates fibrous skeleton of heart
  • Only electrical connection between atria and ventricles
  • Ensures synchronised chamber contraction

Divisions

  • Divides into two main pathways:
    • Right bundle branch
    • Left bundle branch

BUNDLE BRANCHES

Right Bundle Branch

Right bundle branch 360-degree viewer showing conduction pathway along right side of interventricular septum toward right ventricle and moderator band
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Right Bundle Branch, Preview from the app.

  • Carries impulses along right side of interventricular septum
  • Travels beneath endocardium
  • Directed toward right ventricle
  • Reaches moderator band
    • Muscular band crossing ventricular cavity
  • Branches extensively in right ventricular myocardium

Left Bundle Branch

Left bundle branch 360-degree viewer showing conduction pathway with anterior, intermediate, and posterior fascicles toward left ventricle
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Left Bundle Branch, Preview from the app.

  • Travels beneath endocardium on left side of septum
  • Extends toward left ventricle
  • Divides into three main fascicles:
    • Left anterior fascicle
    • Left intermediate fascicle
    • Left posterior fascicle
Left Anterior Fascicle
  • Courses along superior aspect of left ventricle
  • Directed toward anterolateral papillary muscle
  • Spreads in multiple directions over muscle
  • Facilitates uniform anterior wall contraction
Left Intermediate Fascicle
  • Runs superficially through subendocardium
  • Travels along septum toward left ventricular apex
  • Ensures septum and apex receive synchronised stimulation
  • Contributes to effective pumping action
Left Posterior Fascicle
  • Travels along inferior aspect of left ventricle
  • Directed toward posteromedial papillary muscle
  • Disperses across muscle
  • Synchronises posterior wall contraction

PURKINJE FIBRES

  • Also called subendocardial branches
  • Terminal portion of bundle branches
  • Specialised conducting fibres
  • Form extensive network lining inner ventricular walls
  • Penetrate into myocardium
  • Interface directly with cardiac muscle cells
  • Enable rapid and synchronised impulse transmission
  • Result in coordinated and forceful ventricular contraction

FUNCTIONAL SIGNIFICANCE

  • Simultaneous ventricular contraction
  • Efficient blood ejection into:
    • Pulmonary artery from right ventricle
    • Aorta from left ventricle
  • Precise conduction maintains cardiac rhythm and synchrony
  • Disruptions can cause:
    • Arrhythmias
    • Conduction blocks
    • Reduced cardiac output
    • Compromised cardiovascular health

BIBLIOGRAPHY

1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 4th ed. Philadelphia: Elsevier; 2020. Chapter 3: Thorax.

2. Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Edinburgh: Elsevier; 2021. p. 996-1046.

3. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018. p. 127-162.

4. Anderson RH, Yanni J, Boyett MR, Chandler NJ, Dobrzynski H. The anatomy of the cardiac conduction system. Clin Anat. 2009;22(1):99-113.

QUICK FACTS: MYOCARDIUM AND CONDUCTING SYSTEM

Key questions answered about this anatomy topic

Which part of the heart has the thickest myocardium?

Answer: Left ventricle. The left ventricle has the thickest myocardium due to the systemic pressure demands. It must generate enough force to pump blood throughout the entire body, requiring a much thicker muscular wall than the other chambers.

Where is the vortex of the heart located?

Answer: Cardiac apex. The vortex of the heart is located at the cardiac apex, where both ventricles meet. Here, muscle fibres twist and spiral, which promotes efficient contraction of the heart.

What is the primary function of the cardiac conducting system?

Answer: Generating and transmitting electrical impulses. The cardiac conducting system is a specialised network that generates and transmits electrical impulses, ensuring coordinated cardiac muscle contraction and maintaining the heart rhythm.

What is the sinoatrial (SA) node commonly called?

Answer: The natural pacemaker of the heart. The sinoatrial node is known as the natural pacemaker of the heart because it generates the electrical impulses that initiate each heartbeat and determine the heart rate.

Where is the SA node located?

Answer: Right atrium near the superior vena cava opening. The SA node is located in the right atrium near the superior vena cava opening, within the terminal groove. This tadpole-shaped structure initiates the electrical impulses that spread throughout the atria.

Want to test yourself? Try the interactive quiz above!

⋮⋮ Myocardium and Conducting System Quiz
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