Introduction
The vagus nerve (also called the vagal nerve) is one of the 12 cranial nerves, which are nerves that start in the brain and control most body functions. It is the tenth cranial nerve, and medical scientists typically describe it as the longest cranial nerve. From its origin in the brain, the vagus nerve sends many nerve fibres to organs and tissues. Nerve fibres are cordlike projections from your neurons (nerve cells). These nerve fibres and their branches control the functions of glands and smooth muscles in most of your internal organs. Vagus nerve damage or injury can lead you to develop various medical conditions. These include problems with speech or swallowing and gastrointestinal dysfunction, which could lead to digestive issues.
Anatomy of the Vagus Nerve
The autonomic nervous system is a part of your nervous system, which altogether makes up your brain, spinal cord, and the nerves throughout your body. The autonomic nervous system controls unconscious activities such as digestion, sweating, and breathing. It consists of two parts, which are the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system controls your “fight or flight” response, which enables you to fight or flee when you face danger. In contrast, the parasympathetic nervous system allows you to rest and relax. The two autonomic nervous systems function to help keep your body in a balanced state.
Structure
Your vagus nerve consists of two different types of nerve fibres. First, there are somatic nerves, which control sensations around your skin and muscles. The second type is visceral fibres, which regulate the functions of your internal organs. The vagus nerve starts from the medulla oblongata, which is a region found in the base of your brain. It exits the skull through the jugular foramen, a small channel at the base of your skull. Outside the brain, the vagus nerve connects and distributes nerve branches. Most of these nerve fibres supply nerve impulses to your local connective tissues, blood vessels, and organs, directing them as to what they should do.
Location
The right and left vagus nerves exit your brain and travel downwards in your neck. They lie along the carotid sheaths, which are protective covering of connective tissues. Here, both vagus nerves are close to the major blood vessels in your neck. These are the internal and common carotid arteries and the internal jugular vein. In the neck, the vagus nerve divides into four major nerve branches—pharyngeal branches, the superior laryngeal nerve, the recurrent laryngeal nerve, and the superior cardiac nerve. These nerves control the muscles and vessels in your neck. As the vagus nerve descends, it enters your lung cavities (the air space within your lungs) and intestines. At these locations, it divides into multiple terminal nerve fibres that supply the blood vessels, connective tissues, and internal organs in these regions with nerve impulses.
Anatomical Variations
The course and distribution of the vagus nerves vary for each person. A 2022 research study found that the vagus nerve had different anatomical locations in 34% of the study participants . Other studies have found significant anatomical variability of the vagus nerve, especially at the oesophageal hiatus, the opening in the diaphragm where the oesophagus passes into the abdominal cavity. Awareness of these anatomical variations is crucial for surgeons to prevent accidental injuries during surgeries around the neck or the area between the stomach and oesophagus.
Functions of the Vagus Nerve
The vagus nerve works by using its branches to provide both sensing and controlling signals to many organs. The brain controls most systemic functions in the body through its connection with vagus nerve fibers. Involuntary functions of the vagus nerve include,
1, Breathing - The vagus nerve branches in the lung cavity control your breathing by coordinating the rhythmic movements of your diaphragm and rib cage muscles.
2, Gastrointestinal functions - The vagal nerve fibres control the functions of your stomach and intestines, such as bowel movements and the production and discharge of gastrointestinal digestive enzymes. These activities are necessary for proper digestion .
3, Cardiovascular functions - The vagus nerve fibres supply your heart muscles and blood vessels with nerve impulses, regulating your heart rate, blood pressure, and the force of contraction in the heart muscles .
4, Other involuntary actions - The vagus nerve sends sensory and motor fibres to various tissues, including skin receptors and smooth muscles in the neck and intestine, controlling actions such as coughing, sneezing, salivation, swallowing, and vomiting.
Associated Conditions
Damage to the vagus nerve can lead to various medical conditions, including
1, Speaking and Swallowing Difficulties - Injury to the vagus nerve branch supplying the larynx (voice box) and throat can cause speaking difficulties and difficulty swallowing. Symptoms may include a crackly or hoarse voice, altered pain sensations around the affected area, and loss of the gag reflex .
2, Cardiovascular Dysfunction - Damage to the vagal nerve fibres to the heart and blood vessels can alter your heart rate, blood pressure, and the force of your heart’s contraction. Symptoms may include low blood pressure, abnormal heart rate, and fainting spells .
3, Gastrointestinal Dysfunction - Vagal nerve injury to the gastrointestinal tract can interfere with digestion, causing symptoms such as nausea, vomiting, delayed gastric emptying, abdominal pain, bloating, and gastric acid reflux .
Diagnostic Testing
Various assessment methods can be used to check the function of your vagus nerve. These include clinical assessment, where your healthcare provider reviews your medical history and conducts a physical exam, and the Valsalva manoeuvre, a breathing technique to stimulate the vagus nerve’s parasympathetic effects .
Tips for Keeping Your Vagus Nerve Healthy
Proper dietary and lifestyle activities can assist in keeping your vagus nerve healthy. Examples include regular deep breathing practices, yoga, light to moderate physical activities like walking, and the intake of anti-inflammatory foods such as salmon, green leafy vegetables, and berries.
The vagus nerve is a crucial component of the nervous system, controlling many involuntary functions and influencing various organ systems. Awareness of its anatomy, functions, and associated conditions is essential for maintaining overall health and preventing potential complications from nerve damage .