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The heart is innervated by parasympathetic and sympathetic fibres, with the medulla being the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels. The heart's atrial muscle is innervated by vagal efferents, while the ventricular myocardium is only sparsely innervated by vagal efferents. This selective innervation helps to modulate cardiac output efficiently.
| Characteristics | Values |
|---|---|
| Innervated by | Parasympathetic and sympathetic fibres |
| Atrial muscle innervated by | Vagal efferents |
| Ventricular myocardium innervated by | Sparsely innervated by vagal efferents |
| Vagus nerve reduces heart rate by | Releasing acetylcholine at synapses within cardiac ganglia situated around the heart |
| Primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels | The medulla |
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What You'll Learn
- The heart is innervated by parasympathetic and sympathetic fibres
- The medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow
- Atrial muscle is innervated by vagal efferents
- The ventricular myocardium is sparsely innervated by vagal efferents
- The vagus nerve reduces the heart rate by releasing acetylcholine
The heart is innervated by parasympathetic and sympathetic fibres
Atrial muscle is also innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. This selective innervation helps modulate cardiac output efficiently. Studies have revealed significant muscarinic receptor distribution and direct vagal influence on ventricular myocytes, affecting electrophysiology and contractility.
The cardiac muscle is densely innervated by the myocardium, and the direct interaction between SN and myocardial target cells suggests that neuro-cardiac coupling may occur at specific junctional sites. The left bundle branch fans out into interconnecting fascicles, which then ramify into thinner and thinner strands toward the apex. The right bundle branch, a cord-like structure, is a direct continuation of the AV bundle.
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The medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow
The heart is innervated by parasympathetic and sympathetic fibres. The medulla oblongata is the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels. The hypothalamus and higher centres modify the activity of the medullary centres and are particularly important in regulating cardiovascular responses to emotion and stress. The parasympathetic control of the heart is primarily mediated by the vagus nerve, which significantly influences the heart rate and rhythm. The vagus nerve originates in the brainstem at the medulla oblongata and has three nuclei in the central nervous system associated with cardiovascular control: the dorsal motor nucleus, the nucleus ambiguus, and the solitary nucleus. The vagus nerve reduces the heart rate by releasing acetylcholine at synapses within cardiac ganglia situated around the heart. This neurotransmitter binds to muscarinic receptors, leading to a decreased heart rate and reduced force of contraction.
The sympathetic system (thoracolumbar division) originates from the thoracolumbar region of the spinal cord and radiates out towards the target organs. In contrast, the parasympathetic system originates within the midbrain, pons, and medulla oblongata of the brain stem, and part of these fibres originate in the sacral region of the spinal cord. The sympathetic and parasympathetic divisions typically function in opposition to each other, but this opposition is better termed complementary in nature rather than antagonistic. The structural details, demonstrating the dense innervation of the myocardium, and the direct interaction between SN and myocardial target cells, suggest that neuro-cardiac coupling may occur at specific junctional sites.
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Atrial muscle is innervated by vagal efferents
The heart is innervated by parasympathetic and sympathetic fibres. The medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels. Atrial muscle is innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. This selective innervation helps modulate cardiac output efficiently.
Studies have revealed significant muscarinic receptor distribution and direct vagal influence on ventricular myocytes, affecting electrophysiology and contractility. This effect is achieved through interactions that counteract sympathetic activity, demonstrating a refined balance between the two autonomic systems. The vagus nerve reduces the heart rate by releasing acetylcholine at synapses within cardiac ganglia situated around the heart. This neurotransmitter binds to muscarinic receptors, leading to a decreased heart rate and reduced force of contraction.
The structural details, demonstrating the dense innervation of the myocardium, and the direct interaction between SN and myocardial target cells, suggest that neuro-cardiac coupling may occur at specific junctional sites. The fascicles then ramify into thinner and thinner strands toward the apex. The right bundle branch, a cord-like structure, is a direct continuation of the AV bundle.
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The ventricular myocardium is sparsely innervated by vagal efferents
The ventricular myocardium is only sparsely innervated by vagal efferents. This is in contrast to the atrial muscle, which is also innervated by vagal efferents but to a greater extent. The ventricular myocardium is a part of the heart muscle that undergoes changes in inotropy when the body is under stress. The myocardium is densely innervated, with the vagus nerve reducing the heart rate by releasing acetylcholine at synapses within cardiac ganglia situated around the heart. This neurotransmitter binds to muscarinic receptors, leading to a decreased heart rate and reduced force of contraction. This effect is achieved through interactions that counteract sympathetic activity, demonstrating a refined balance between the two autonomic systems. The medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels.
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The vagus nerve reduces the heart rate by releasing acetylcholine
The heart is innervated by parasympathetic and sympathetic fibres. The vagus nerve is a parasympathetic nerve that plays a crucial role in reducing the heart rate. It does so by releasing acetylcholine, a neurotransmitter, at synapses within cardiac ganglia situated around the heart. Acetylcholine binds to muscarinic receptors, leading to a decreased heart rate and reduced force of contraction. This phenomenon is known as "accentuated antagonism".
The vagus nerve's role in reducing heart rate is particularly important during heightened sympathetic activity, which occurs when the body is under stress. During these times, the sympathetic nervous system releases stress hormones such as cortisol and adrenaline, increasing the heart rate. The vagus nerve counteracts this by releasing acetylcholine, which binds to inhibitory G proteins (Gi) and prevents the production of cyclic adenosine monophosphate (cAMP), ultimately slowing down the heart rate.
The right vagus nerve primarily innervates the sinoatrial (SA) node, while the left vagus nerve innervates the atrioventricular (AV) node. However, there can be significant overlap in their anatomical distribution. The vagus nerve's ability to reduce heart rate by releasing acetylcholine highlights its clinical importance, particularly in regulating arrhythmogenesis and protecting against ventricular fibrillation.
The vagus nerve's influence on the heart rate is a complex process involving the interaction of multiple systems and receptors. It is regulated by the medulla, the primary site in the brain for controlling sympathetic and parasympathetic outflow to the heart and blood vessels. The vagus nerve's ability to release acetylcholine and slow down the heart rate demonstrates the body's refined balance between the sympathetic and parasympathetic systems.
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Frequently asked questions
The heart is innervated by parasympathetic and sympathetic fibres. The medulla is the primary site in the brain for regulating sympathetic and parasympathetic outflow to the heart and blood vessels.
The vagus nerve reduces the heart rate by releasing acetylcholine at synapses within cardiac ganglia situated around the heart. This neurotransmitter binds to muscarinic receptors, leading to a decreased heart rate and reduced force of contraction.
The entire heart muscle undergoes changes in inotropy at the same time. This response is regulated by the sympathetic nervous system, which operates on a beat-to-beat basis.
Atrial muscle is innervated by vagal efferents, whereas the ventricular myocardium is only sparsely innervated by vagal efferents. This selective innervation helps modulate cardiac output efficiently.
