What Is a Vasovagal Response?

The vagus nerve is a mixed nerve. Its motor fibers originate from the suspicious nucleus and run parallel to the glossopharyngeal nerve. After passing through the brain stem, it exits the cranial cavity through the jugular foramen. The sensory neurons are in the cervical ganglia and nodal ganglia near the jugular foramen. The peripheral branches of the cervical ganglion conduct part of the general sensations of the external auditory canal, tympanic membrane, and auricle; the central branch branches into the spinal nucleus of the brain stem of the trigeminal nerve. The peripheral branches of the nodular ganglion conduct the sensations of the pharynx, larynx, trachea, esophagus, and internal organs, as well as the taste of the pharynx, soft palate, hard palate, and epiglottis; the central branch enters the arcuate nucleus. Parasympathetic nerves originate from the dorsal nucleus of the vagus nerve at the bottom of the fourth ventricle and are distributed to internal organs.

The vagus nerve is a mixed nerve. Its motor fibers originate from the suspicious nucleus and run parallel to the glossopharyngeal nerve. After passing through the brain stem, it exits the cranial cavity through the jugular foramen. The sensory neurons are in the cervical ganglia and nodal ganglia near the jugular foramen. The peripheral branches of the cervical ganglion conduct part of the general sensations of the external auditory canal, tympanic membrane, and auricle; the central branch branches into the spinal nucleus of the brain stem of the trigeminal nerve. The peripheral branches of the nodular ganglion conduct the sensations of the pharynx, larynx, trachea, esophagus, and internal organs, as well as the taste of the pharynx, soft palate, hard palate, and epiglottis; the central branch enters the arcuate nucleus. Parasympathetic nerves originate from the dorsal nucleus of the vagus nerve at the bottom of the fourth ventricle and are distributed to internal organs.

Chinese name

Vagus nerve

Foreign name

(vagus nerve)

Function

Dominate the two systems of breathing and digestion

Nature

Mixed nerve

Make up

Four fiber components

Definition

10th pair of brain nerves

Vagus nerve fiber composition

Contains four kinds of fibers: somatic, visceral, visceral, and somatic.

1. Body movement fiber: Skeletal muscles that control the throat, can move freely.

2. Visceral motor parasympathetic fiber: It is the main component of the vagus nerve and is distributed in thoracic internal organs (such as trachea, bronchus, lung, heart, etc.) and abdominal internal organs (such as liver, pancreas, spleen, kidney, adrenal gland, and stomach to transverse colon Digestive tract, etc.), regulate the activities of these organs.

3. Visceral sensory fibers: Conduct the sensory impulses of the viscera in the chest and abdomen.

4. Somatosensory fibers: Conduct the general sensations of the auricle, external auditory canal, and pleura. Vagus nerve trunk injury is characterized by increased heart rate, nausea, vomiting, and slow breathing. Due to the paralysis of the throat muscles, hoarseness, speech difficulties, and swallowing disorders can occur.

Physiological characteristics of vagus nerve

The vagus nerve has multiple branches in the neck, chest, and abdomen, which dominate the neck, intrathoracic organs, and most of the organs in the abdominal cavity. It regulates circulation through the sensory impulses of the organs and organs and controls the activity of the heart muscle, smooth muscle, and glands. Respiratory and digestive systems.

(1) Circulation system:

The parasympathetic ganglia fibers that dominate the heart walk in the vagus nerve trunk. The cell bodies of these preganglionic neurons are located in the dorsal and skeletal nucleus of the medulla oblongata. Postganglionic fibers dominate the sinoatrial node, atrioventricular junction, atrial muscle, atrioventricular bundle and its branches. The right vagus nerve mainly governs the sinoatrial node, and the left vagus nerve mainly governs the atrioventricular junction area. The vagus nerve also governs the ventricular muscle, but its The number of fiber ends is much less than in the atrial muscle. The acetylcholine (Ach) released from the fiber end of the cardiac vagus ganglia after acting on the M-type cholinergic receptors on the myocardial cell membrane can cause slow heart rate (ie, negative frequency effect) and slow atrioventricular node conduction (ie, negative Sexual conduction effect), atrial muscle contraction is weakened (ie, negative muscle effect), and it also has a direct inhibitory effect on ventricular muscles, but atrial muscles are more sensitive to Ach than ventricles. In addition, Ach released from the vagus nerve fiber end binds to M-type cholinergic receptors of vascular smooth muscle, leading to the release of nitric oxide and causing vasodilation. Aortic arch baroreceptor afferent nerve fibers walk within the vagus nerve, enter the medulla oblongata and reach NTS. When the arterial blood pressure rises, the afferent impulse of the baroreceptor increases, and through related cardiovascular central integration, the heart vagus tension, heart sympathy, and sympathy Reduced vasoconstriction has the effect of slowing heart rate, reducing cardiac output, reducing peripheral vascular resistance, and lowering arterial blood pressure, and vice versa when arterial blood pressure increases, thereby rapidly adjusting arterial blood pressure. Sensory signals from chemoreceptors in the aorta are also transmitted to NTS via the vagus nerve, which changes cardiovascular activity during hypoxia, suffocation, blood loss, hypo-arterial blood pressure, and acidosis.

(B) the respiratory system:

The vagus nerve bronchus branch and the sympathetic nerves together form the lung plexus, which issues thin branches to control the bronchi and lungs. Ach released from the vagus nerve terminal binds to the airway surface epithelial and secretory cell M-type cholinergic receptors, causing increased ciliary swing frequency and increased airway mucus secretion, and binding to the M-type cholinergic receptors of bronchial smooth muscle, causing bronchial smooth muscle spasm , Bronchoconstriction, increased airway tension. In the lungs, the vagus nerve participates in lung dilatation reflexes. When the lungs are dilated, the airway is stretched, expanding the airway, stimulating the stretch receptors, transmitting impulses along the vagus nerve into the medulla, accelerating the inhalation process into the exhalation process, and increasing the breathing rate. In addition, aortic chemoreceptors are stimulated when the arterial blood oxygen partial pressure decreases, the arterial carbon dioxide partial pressure or hydrogen ion concentration increases, and the sensory signal is transmitted to the NTS through the vagus nerve, which reflexively causes the deepening of breathing to accelerate.

(3) Digestive system:

In the cervical and thorax, the branch of the superior laryngeal nerve of the vagus nerve mainly dominates the ciliate muscle, strains the vocal cords, and conducts general visceral sensory impulses in the distribution area. The motor fibers of the recurrent laryngeal nerve branch of the vagus nerve dominate all laryngeal muscles except the ciliary thyroid muscle, and the sensory fibers are distributed in the laryngeal mucosa below the glottis. The pharyngeal branch of the vagus nerve controls the movement of the pharyngeal contractile and soft palate muscles and the pharyngeal mucosa. Therefore, when one side of the vagus nerve is injured, the affected laryngeal muscle may be paralyzed, and the throat mucosal sensory conduction disorder may cause the affected side pharyngeal reflex and the affected side laryngeal cough reflex to disappear. The clinical manifestations are hoarseness, speech disturbance, and swallowing. Obstacles or choking. When bilateral vagus nerve damage occurs, swallowing disorders, slow breathing, severe difficulty breathing, or asphyxia. In the abdomen, prevagal ganglion fibers enter the gastrointestinal tissue and form synapses with the neurons of the intermuscular plexus and submucosal plexus. The postganglionic fibers dominate glandular cells, epithelial cells, blood vessels, and smooth muscle cells of the digestive tract. Ach released from the fiber end of the vagus ganglion activates M-type cholinergic receptors, which causes the digestive tract to contract and increase glandular secretion, while the digestive sphincter is relaxed.