Vagus nerve: what it is and what functions it has in the nervous system

The vagus nerve is number 10 of the cranial nerves.. Among other things, it is responsible for transmitting information related to sensory and muscular activity, as well as anatomical functions.

Next we will briefly see what the cranial nerves are, and later we will define the vagus nerve.

• Related article: "Parts of the Nervous System: functions and anatomical structures"

cranial nerves

The lower part of our brain is made up of a complex network of nerves that we know as “cranial nerves” or “cranial nerves”. In total there are 12 originate directly in our brain and they are distributed along different fibers by means of holes that are in the base of the skull towards the neck, the thorax and the abdomen.

Each of these nerves is made up of fibers that fulfill different functions and that arise from a specific part of the brain (it can be at the base or in the stem). Depending on their location and the specific place they depart from, cranial nerves are divided into subgroups:

• On the stem are pairs I and II.
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• Pairs III and IV are found in the midbrain.
• On the Varolio bridge are the V, VI, VII and VIII.
• Finally, in the medulla oblongata are the IX, X, XI and XII.

At the same time, each one of them has different names according to its origin, its activity, or the specific function that they comply In the following sections we will see how it is defined and what functions the vagus nerve has.

What is the vagus nerve?

The vagus nerve is one of the cranial nerves that is distinguished by having four nuclei and five different types of fiber. Specifically, it is the cranial nerve number X and it is the most predominant neural effector of the parasympathetic nervous system, since it comprises 75% of all its nerve fibers (Czura & Tracey, 2007).

It is known as the “vagus” nerve to refer to ramblings and detours. It is the nerve whose course is the longest of the cranial nerves, extending and distributing widely below the level of the head.

It arises in the medulla oblongata or medulla oblongata, and advances towards the jugular foramen., passing between the glossopharyngeal and spinal accessory nerves, and is composed of two ganglia: one superior and one inferior.

starting from medulla oblongata and through the jugular foramen, the vagus nerve descends towards the thorax, crossing different nerves, veins and arteries. Both its left and right parts extend inside the neck to the thorax; For this reason, it is responsible for carrying part of the parasympathetic fibers to the thoracic viscera.

The vagus nerve especially interacts with the immune system and the central nervous system and performs motor functions in the larynx, diaphragm, stomach, heart. It also has sensory functions in the ears, tongue, and visceral organs such as the liver.

Damage to this nerve can cause dysphagia (trouble swallowing), or incomplete closure of the oropharynx and nasopharynx. On the other hand, pharmacological interventions on the vagus nerve can help control different pains, for example those that are caused by cancer and by tumors of the larynx or intrathoracic diseases.

• You may be interested in: "Parasympathetic nervous system: functions and route"

Connection with other nerves

As we saw before, the vagus nerve connects with different nerves, that is, it exchanges several of its fibers and functions. According to Barral, J-P. & Croibier, A. (2009), the nerves with which it connects are the following:

• Accessory nerve.
• Glossopharyngeal nerve.
• Facial nerve.
• Hypoglossal nerve.
• sympathetic nerve.
• The first two spinal nerves.
• Phrenic nerve.

Its 5 types of fibers and their functions

Nerve fibers, or nerves, are the processes that connect the center of each nerve cell to the next. They transmit signals known as action potentials. and allow us to process stimuli.

The latter are not the only types of fibers, there are also those used to connect and activate effector organs, muscle fibers or glands. According to Rea (2014), the vagus nerve has the following types of fibers.

1. brachial motor fiber

activates and regulates the muscles of the pharynx and larynx.

2. sensory visceral fiber

Responsible for transmitting information from a wide variety of organssuch as the heart and lungs, the pharynx and larynx, and the uppermost part of the gastrointestinal tract.

3. visceral motor fiber

It is responsible for carrying the parasympathetic fibers from smooth muscle to the respiratory tract, heart, and gastrointestinal tract.

4. special sensory fiber

The vagus nerve transmits information necessary for taste to the palate and the epiglottis (the fibrous cartilage that closes the entrance to the larynx during swallowing).

5. general sensory fiber

This component allows the passage of information from parts of the ear and the dura mater within the posterior cranial fossa.

Bibliographic references:

• Barral, J-P. (2009). Vagus nerve. Manual Therapy for the Cranial Nerves. Elsevier: USA.
• Rhea, P. (2014). Vagus Nerve. Clinical Anatomy of the Cranial Nerves. Elsevier Academic Press: UK.
• Czura, C. (2007). Cholinergic Regulation of Inflammation. Psychoneuroimmunology (Fourth Edition). Elsevier Academic Press: USA.
• Waldman, S. (2007). Pain management. Saunders: USA.