MYOCARDIUM AND CONDUCTING SYSTEM
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Myocardium - Cardiac Muscle Layer, Preview from the app.
MYOCARDIUM
What is the myocardium?
- Thick muscular layer of your heart wall
- Responsible for your heart's contractile function
- Composed primarily of cardiac muscle cells
Thickness Variation
How does myocardial thickness vary?
- Thinner in atria
- Significantly thicker in ventricles
- Left ventricle thickest due to systemic pressure demands
- Right ventricle thinner as it pumps to your pulmonary circulation
Vortex of the Heart
What is the 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
Conducting System Overview, Preview from the app.
What is the conducting system of the heart?
- Specialised network embedded within your myocardium
- Generates and transmits electrical impulses
- Ensures coordinated cardiac muscle contraction
- Regulates your heartbeat and maintains rhythm
Components
What are the components of the conducting system?
- Sinoatrial node
- Atrioventricular node
- Atrioventricular bundle
- Bundle branches
- Purkinje fibres
SINOATRIAL NODE
Sinoatrial Node (SA Node), Preview from the app.
What is the sinoatrial node?
- Natural pacemaker of your heart
- Tadpole-shaped structure
- Generates electrical impulses
- Impulses spread throughout your atria first
Location
Where is the sinoatrial node located?
- Right atrium
- Near superior vena cava opening
- Within terminal groove
ATRIOVENTRICULAR NODE
Atrioventricular Node (AV Node), Preview from the app.
What is the atrioventricular node?
- Specialised cluster of cells
- Functions as a critical gateway
- Briefly delays impulse transmission
- Delay allows your atria to fully contract
- Ensures atrial blood empties into your ventricles before ventricular contraction
Location
Where is the atrioventricular node located?
- Right atrium near septum
- Within Triangle of Koch
ATRIOVENTRICULAR BUNDLE
Atrioventricular Bundle (Bundle of His), Preview from the app.
What is the atrioventricular bundle?
- Also known as Bundle of His
- Composed of specialised conducting fibres
- Penetrates fibrous skeleton of your heart
- Only electrical connection between atria and ventricles
- Ensures synchronised chamber contraction
Divisions
How does the atrioventricular bundle divide?
- Divides into two main pathways:
- Right bundle branch
- Left bundle branch
BUNDLE BRANCHES
Right Bundle Branch
What is the right bundle branch?
- Carries impulses along right side of interventricular septum
- Travels beneath endocardium
- Directed toward your right ventricle
- Reaches moderator band
- Muscular band crossing ventricular cavity
- Branches extensively in right ventricular myocardium
Left Bundle Branch
What is the left bundle branch?
- Travels beneath endocardium on left side of septum
- Extends toward your left ventricle
- Divides into three main fascicles:
- Left anterior fascicle
- Left intermediate fascicle
- Left posterior fascicle
What is the 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
What is the left intermediate fascicle?
- Runs superficially through subendocardium
- Travels along septum toward left ventricular apex
- Ensures septum and apex receive synchronised stimulation
- Contributes to your heart's effective pumping action
What is the left posterior fascicle?
- Travels along inferior aspect of left ventricle
- Directed toward posteromedial papillary muscle
- Disperses across muscle
- Synchronises posterior wall contraction
PURKINJE FIBRES
What are the Purkinje fibres?
- Also called subendocardial branches
- Terminal portion of bundle branches
- Specialised conducting fibres
- Form extensive network lining your 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
Why is the conducting system functionally significant?
- Simultaneous ventricular contraction
- Efficient blood ejection into:
- Pulmonary artery from your right ventricle
- Aorta from your left ventricle
- Precise conduction maintains your cardiac rhythm and synchrony
- Disruptions can cause:
- Arrhythmias
- Conduction blocks
- Reduced cardiac output
- Compromised cardiovascular health
BIBLIOGRAPHY
1. Gray H, Lewis W. Angiology. In: Anatomy of the Human Body. 1918. p. 526–542.
2. Gosling JA, Harris PF, Humpherson JR, Whitmore I, Willan PLT. Human anatomy: color atlas and textbook. 6th ed. 2017. 45–58 p.
3. Anderson RH, Spicer DE, Hlavacek AM, Cook AC, Backer CL. (2013). Anatomy of the cardiac chambers. In Wilcox’s Surgical Anatomy of the Heart (4th ed., pp. 13–50). Cambridge University Press.
4. Fritsch H, Kuehnel W. Color Atlas of Human Anatomy. Vol. Volume 2, Color Atlas and Textbook of Human Anatomy. 2005. 10–42 p.
5. Moore K, Dalley A, Agur A. Clinically Oriented Anatomy. Vol. 7ed, Clinically Oriented Anatomy. 2014. 132–151 p.
6. Ho SYen. Anatomy for Cardiac Electrophysiologists: A Practical Handbook. Cardiotext Pub; 2012. 5–27 p.