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Table of Contents
- Course Home
- Objectives
- Matching Exercise
- Introduction
- Anatomy: The Heart
- Anatomy: The Vessels
- Physiology: Introduction
- Physiology: Review of Circulation
- Physiology: The Cardiac Cycle
- Physiology: Innervation of the Heart
- Cardiac Electrophysiology: Introduction
- Cardiac Electrophysiology: Electrolytes
- Cardiac Electrophysiology: Cardiac Automaticity
- Cardiac Electrophysiology: The Cardiac Conduction System
- Cardiac Electrophysiology: Myocardial Contraction
- Sample Cases
- Case 1: Cardiac Tamponade
- Figure 1: Assessment
- Figure 2: Management
- Case 2: Cocaine Overdose
- Figure 3: Assessment
- Figure 4: Management
- Case 3: Hemorrhagic Shock
- Figure 5: Assessment
- Figure 6: Management
- Conclusion
- References
- Bibliography
Cardiac Electrophysiology: Myocardial Contraction
Introduction:
Once the electrical signal has been generated in the pacemaker cells, and has propagated through the cardiac conduction system, it is then very rapidly transmitted from one myocardial cell to the next so as to achieve a synchronized contraction.
The Intercalated Disc:
The electrical signal is able to pass quickly among the myocardial cells due to a unique structural component of cardiac cells known as the intercalated disc. Intercalated discs are specialized junctions that exist between myocardial cells, which function to increase the rate at which action potentials can be spread from cell to cell.
The Contraction of the Heart as a Coordinated Unit:
Due to this rapid spread of action potentials, cardiac muscle is able to function and contract as a coordinated unit. This coordinated unit of contraction is known as a syncytium and allows the heart to function according to an “all or nothing” principle. That is, if a single muscle fiber is depolarized, the action potential will spread throughout the entire syncytium and the whole area will contract.
The heart is composed of two syncytia, the atrial syncytium and the ventricular syncytium. The two syncytia are separated by dense fibrous tissue that allows them to act independently. The atrial syncytium contracts from superior to inferior, allowing the atria to function as a unit and squeeze blood into the ventricles. The ventricular syncytium contracts from inferior to superior, so as to push blood into the circulation.