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In most cases, vagal tone is not measured directly. Instead the processes affected by the vagus nerve – specifically heart rate and heart rate variability – are measured and used as a surrogate for vagal tone. Increased vagal tone (and thus vagal action) is generally associated with a lower heart rate and increased heart rate variability.
Vagusstoff (literally translated from German as "Vagus Substance") refers to the substance released by stimulation of the vagus nerve which causes a reduction in the heart rate. Discovered in 1921 by physiologist Otto Loewi , vagusstoff was the first confirmation of chemical synaptic transmission and the first neurotransmitter ever discovered.
As a general consideration, increased vagal tone (and thus vagal action) is associated with a diminished and more variable heart rate. [ 18 ] [ 19 ] The main mechanism by which the parasympathetic nervous system acts on vascular and cardiac control is the so-called respiratory sinus arrhythmia (RSA).
This is a potential cause of vomiting due to the inability of the proximal stomach smooth muscle to undergo receptive relaxation. The vagal afferents are activated during the gastric phase of digestion when the corpus and fundus of the stomach are distended secondary to the entry of a food bolus. The stimulation of the mechanical receptors ...
The mechanism of development of Cushing ulcers is thought to be due to direct stimulation of vagal nuclei as a result of increased intracranial pressure.Brain tumors, traumatic head injury, and other intracranial processes including infections, can cause increased intracranial pressure and lead to overstimulation of the vagus nerve. [3]
Methyldopa acts on the vasomotor center, leading to selective stimulation of α 2-adrenergic receptor. [8] Guanfacine also causes the same stimulation. [9] This reduces sympathetic tone to vascular smooth muscle. [9] This reduces heart rate and vascular resistance. [9] Digoxin increases vagal tone from the vasomotor centre, which decreases ...
In a worst-case scenario, if the flare also spawns a supersize coronal mass ejection that happens to be aimed at Earth, it could cause a violent geomagnetic storm, inducing electric currents that ...
The stimulation of the J-receptors causes a reflex increase in breathing rate, and is also thought to be involved in the sensation of dyspnea, the subjective sensation of difficulty breathing. [ 4 ] [ 5 ] The reflex response that is produced is apnea followed by rapid breathing, bradycardia , and hypotension (pulmonary chemoreflex).