Anatomy
Summary
The vagus nerve (CN X) serves as a major conduit for parasympathetic innervation to thoracoabdominal organs, affecting the heart, lungs, and the gastrointestinal tract up to the splenic flexure. It plays a critical role in slowing the heart rate by modulating the SA node and AV node, and in reducing systemic vascular resistance through vasodilation, collectively termed the vasovagal reaction. Additionally, CN X carries afferent signals from baroreceptors and chemoreceptors in the aortic arch, participating in reflex loops that regulate cardiovascular functions.
In conjunction with CN IX, or the glossopharyngeal nerve, the vagus nerve is implicated in baroreflexes involving the carotid sinus and the aortic arch, effectively lowering heart rate and blood pressure. Carotid sinus massage, can slow the heart rate and is used clinically to terminate tachycardic rhythms. Parasympathetic influence from the vagus nerve also affects the GI tract by increasing gastric acid secretion and GI motility. The anatomical pathway of the vagus nerve makes it vulnerable to injury, especially as it passes through the esophageal hiatus as anterior and posterior vagal trunks.
Lesson Outline
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FAQs
The vagus nerve, or cranial nerve X, plays a central role in the parasympathetic system. This nerve regulates the functions of the heart, lungs, peripheral vasculature, and proximal digestive tract to the splenic flexure. It helps to slow the heart rate, stimulate digestion, promote saliva production, and stimulate gastric secretion, among other functions.
Vagal parasympathetics help reduce the heart rate and lower blood pressure. This effectively impacts the peripheral vasculature by causing vessel dilation, reducing the overall workload on the heart.
Vasovagal syncope is a sudden drop in heart rate and blood pressure that results in fainting, often in response to a stressful trigger. This happens because of overstimulation of the vagus nerve, resulting in bradycardia and dilation of the peripheral vasculature, reducing systemic vascular resistance and blood flow to the brain.
The baroreceptor reflex helps maintain blood pressure at nearly constant levels. Parasympathetic innervation, mediated by the vagus nerve, is vital to this reflex. When blood pressure rises, the baroreflex is stimulated, and the vagus nerve is activated leading to a decrease in heart rate, cardiac contractility, and ultimately blood pressure.
The vagus nerve plays a crucial role in the regulation of gastrointestinal motility. It provides parasympathetic innervation to the majority of the digestive tract, including the esophagus, stomach, and parts of the small and large intestines. Activation of the vagus nerve can stimulate peristalsis, promoting the movement of food along the digestive tract.
