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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
Physiology: Innervation of the Heart
Introduction:
The heart is controlled by two opposing divisions of the autonomic nervous system – the sympathetic and parasympathetic nervous systems. These two systems will ideally balance each other out and create a steady state. However, during stressful situations the sympathetic nervous system dominates, which leads to tachycardia, increased cardiac output, and increased oxygen demand of the heart. Conversely, during relaxed states, such as sleep, the parasympathetic nervous system predominates, which leads to the resting heart rate, baseline cardiac output, and decreased oxygen demand of the heart.
The Sympathetic Nervous System:
The sympathetic innervation of the heart consists of nerves that arise from the thoracic and lumbar spine and synapse (or connect) with the nervous tissue of the heart, which is known as the cardiac plexus. The nerves of the cardiac plexus serve as a conduit through which certain neurotransmitters (such as norepinephrine and acetylcholine) can travel to reach their target receptors in the heart. The target receptor for the sympathetic nervous system in the heart is the Beta-1-receptor. This receptor is responsible for increasing the heart’s rate and contractility.
When referring to the sympathetic nervous system, the term “adrenergic,” may be used. This term refers to the nerve cells or fibers of the autonomic nervous system that employ norepinephrine as their neurotransmitter. Since norepinephrine is used exclusively in the sympathetic nervous system, one can see how “adrenergic” also implies “sympathetic.”
The Parasympathetic Nervous System:
The parasympathetic nervous system exerts its control on the heart through the vagus nerve, which originates from the brainstem as cranial nerve ten. The vagus fibers connect to the atria and the superior portions of the ventricles. The release of neurotransmitters from the vagus nerve results in a decrease in heart rate and contractility.
When referring to the parasympathetic nervous system, the term, “cholinergic” is often used. This word refers to nerve cells or fibers that employ acetylcholine as their neurotransmitter.