Vagus Nerve: Cranial nerve X

Vagus Nerve (Cranial Nerve 10)

  • The vagus nerve, also known as Cranial Nerve X, is a vital component of the autonomic nervous system, providing an extensive supply to numerous structures within the body. It plays a crucial role in regulating various bodily functions, including heart rate, digestion, and respiration. Damage to the vagus nerve can result in a wide range of clinical issues, underscoring its importance.

  • This lecture will cover:

    • Origin of the nerve: the medulla oblongata in the brainstem.

    • Course of the nerve: traversing from the brainstem through the neck, thorax, and abdomen.

    • Structures supplied: including the pharynx, larynx, esophagus, trachea, lungs, heart, stomach, liver, pancreas, and intestines.

    • Functions of those structures: such as swallowing, speech, breathing, heart rate regulation, digestion, and secretion.

    • Basic clinical correlations: including vagal nerve dysfunction, which can lead to issues like dysphagia (difficulty swallowing), hoarseness, reduced heart rate variability, and digestive problems. Detailed discussion in autonomic nervous system videos, specifically the parasympathetic nervous system.

Fiber Types

The vagus nerve contains a diverse array of fiber types, each responsible for specific functions:

  • GVE (General Visceral Efferent) fibers:

    • These are secreto-motor fibers, which stimulate secretion from various glands and control smooth muscle contraction in organs like the stomach and intestines.

    • Part of the parasympathetic nervous system (detailed discussion in parasympathetic nervous system videos).

  • GVA (General Visceral Afferent) fibers:

    • These fibers transmit sensory information from the internal organs back to the central nervous system, including sensations like fullness, pain, and nausea. Important; discussed in parasympathetic nervous system and other contexts.

  • GSA (General Somatic Afferent) fibers:

    • These fibers carry sensory information from the skin and muscles to the brain, including touch, pain, and temperature sensations.

  • SVA (Special Visceral Afferent) fibers:

    • Responsible for taste sensation from the epiglottis and pharynx, allowing individuals to perceive flavors in these regions.

  • SVE (Special Visceral Efferent) fibers:

    • These fibers innervate muscles derived from the fourth and sixth pharyngeal arches, which are involved in swallowing and speech.

GSA Fibers (Touch, Pain, Temperature)

  • Supply:

    • Tympanic cavity: The air-filled space within the middle ear.

    • Tympanic membrane: Also known as the eardrum, which vibrates in response to sound waves.

    • External acoustic meatus: The ear canal that leads to the tympanic membrane.

    • Patch of skin behind the ear (auricle or pinna).

  • Ganglion:

    • Superior ganglion of cranial nerve 10 (jugular ganglion).

    • Located close to the jugular foramen, the opening through which the vagus nerve exits the skull.

  • Course:

    • Fibers from the supplied structures go to the superior ganglion.

    • Pass through the jugular foramen.

    • Move towards the medulla.

    • Give off an auricular branch.

    • Give off a meningeal branch, which supplies pain fibers to the meninges, the protective membranes surrounding the brain and spinal cord.

  • Destination in the medulla:

    • Spinal nucleus of the trigeminal nerve (cranial nerve 5).

SVA Fibers (Taste)

  • Function:

    • Taste (gustation).

    • Taste buds on the epiglottis (primarily) and a small amount in the pharynx.

    • Sense sweet, salty, bitter, sour, and umami tastes.

  • Ganglion:

    • Inferior ganglion of cranial nerve 10 (nodose ganglion).

  • Course:

    • Central processes from the epiglottis and pharynx.

    • Pass through the jugular foramen.

    • Enter the posterior cranial fossa.

  • Destination in the medulla:

    • Nucleus of tractus solitarius.

SVE Fibers (Motor)

  • Origin:

    • Nucleus ambiguus.

  • Course:

    • Vagus nerve gives off branches.

    • Cranial nerve 11 (accessory nerve) runs with the vagus nerve. Main motor nerve

    • Most internal branches of the accessory nerve travel with the vagus nerve, innervating muscles in the pharynx and larynx.

    • Cranial nerve 9 (glossopharyngeal nerve) also runs with it.

    • These nerves form the pharyngeal plexus, a network of nerves that control the muscles of the pharynx.

  • Supply:

    • Pharynx:

      • Superior, middle, and inferior pharyngeal constrictors, which are involved in deglutition (swallowing).

    • Soft palate:

      • Palatoglossus: pulls the back of the tongue upwards.

      • Palatopharyngeus: elevates the pharynx.

      • Salpingopharyngeus: elevates the pharynx, pulls on the auditory tube.

      • Levator veli palatini: elevates the palate.

      • Muscles of the uvula.

Superior Laryngeal Nerve (Branch of Vagus Nerve, SVE)

  • Course:

    • Branches from the vagus nerve and gets close to the larynx then bifurcates.

    • Gives off two branches:

      • Internal branch of the superior laryngeal nerve: primarily sensory, providing sensation to the larynx above the vocal cords.

      • External branch of the superior laryngeal nerve: primarily motor, supplying the cricothyroid muscle.

  • External Branch Supply:

    • Cricothyroid muscle:

    • Cricoarytenoid.

    • Involved in phonation or speech production, as the cricothyroid muscle adjusts the tension of the vocal cords.

Recurrent Laryngeal Nerve (Branch of Vagus Nerve, SVE)

  • Course:

    • There is a right and left recurrent laryngeal nerve.

    • The right goes underneath the subclavian artery.

    • The left goes underneath the aortic arch.

    • Gives off the inferior laryngeal nerve, which innervates the intrinsic muscles of the larynx.

  • Supply:

    • Intrinsic muscles of the larynx via inferior laryngeal nerve.

    • Posterior and lateral cricoarytenoid muscles.

    • Transverse and oblique arytenoid muscles.

    • Thyroarytenoid muscle.

GVA and GVE Fibers Associated with Laryngeal Nerves

  • Superior Laryngeal Nerve:

    • GVA fibers move with the superior laryngeal nerve.

    • Mainly the internal branch.

    • Pierces the thyrohyoid membrane.

    • Supplies:

      • Mucosa of the larynx above the true vocal cords.

      • Mucosa of the epiglottis.

  • Recurrent Laryngeal Nerve:

    • GVA fibers move with the recurrent laryngeal nerve and inferior laryngeal nerve.

    • Supplies:

      • Mucosa of the larynx below the true vocal cords.

GVA Fibers from Aortic and Carotid Bodies

  • GVA fibers from the aortic arch and carotid bodies.

  • Carotid sinus branch and carotid body branch and aortic arch branch.

  • Course:

    • Move upwards to the inferior ganglion (nodose ganglion).

    • Also receives GVA fibers from the superior laryngeal nerve and recurrent laryngeal nerve.

    • Pass through the jugular foramen.

  • Destination:

    • Nucleus of tractus solitarius.

Parasympathetic Fibers (GVE) to Esophagus and Trachea

  • Some GVE fibers move with the recurrent laryngeal nerve.

  • Supply:

    • Esophagus (for peristalsis).

    • Trachea (for secretion and smooth muscle constriction).

Thoracic and Abdominal Viscera (GVA and GVE Fibers)

  • Vagus nerve gives off several branches to the thoracic and abdominal viscera, containing GVA and GVE fibers.

Pulmonary Plexus

  • Bronchial branches from the vagus nerve form the pulmonary plexus.

  • Supplies:

    • Lungs and associated bronchi.

  • GVA fibers:

    • Afferent fibers from stretch receptors and irritant receptors within the bronchi and trachea.

  • GVE fibers:

    • Secretion or contraction

Cardiac Plexus

  • Superior, inferior, and thoracic cardiac nerves form the cardiac plexus.

  • Intramural (terminal) ganglia located within the heart.

  • Function:

    • GVE fibers slow down heart rate via SA and AV nodes.

Esophageal Plexus

  • Supplies the esophagus to produce peristaltic contractions.

Gastric Nerves

  • Anterior and posterior gastric nerves originate from the esophageal plexus.

  • Supply the stomach to aid peristalsis and mechanical digestion.

Celiac Plexus

  • Originates from the right vagus nerve.

  • Supplies:

    • Adrenal glands

    • Kidneys

    • Large intestine (up to the splenic flexure)

    • Small intestine.

    • Pancreas (for secretion of pancreatic juices)

    • Spleen

Hepatic Plexus

  • Originates from the left vagus nerve.

  • Supplies:

    • Liver

    • Gallbladder

Clinical Correlations

  • Damaged vagus nerve can result in a negative gag reflex.

  • If the vagus nerve is damaged: Uvulamovestotheoppositesideofthelesion.Uvula moves to the opposite side of the lesion.

    • Example: If the right vagus nerve is damaged, the uvula moves to the left.

  • Damage to nerves supplying thoracic and abdominal viscera can lead to various issues, such as:

    • Inability to slow heart rate.

    • Impaired secretion or peristaltic activities in the abdominal viscera.