VAN 121: Veterinary Gross Anatomy-II (2+2)

Vagus nerve

VAGUS OR PNEUMOGASTRIC NERVE

• This is a mixed nerve.
• It is the longest and the most widely distributed of all the cranial nerves.
• It is attached to the lateral aspect of the medulla oblongata by several filaments, which arise in a series with those of the glossopharyngeal in front and the spinal accessory behind.
• The bundles converge to form a trunk that passes outward pierces the dura and emerges out of the cranium through the foramen lacerum. In the foramen, it bears the jugular ganglion. Beyond this, it runs backward and downward with the eleventh cranial nerve. Then the two nerves separate and the twelfth cranial nerve passes between them.
• It descends along with cervical sympathetic to form a common vago-sympathetic cord on the dorsal part of the carotid sheath above carotid artery and descends deeply in the jugular furrow and enters the thorax.

Collateral branches

• The right vagus crosses under the right brachial artery across the trachea, reaches the oesophagus behind the aortic arch and divides into dorsal and ventral branches.
• The left vagus enters the thoracic cavity, passes under the arch of the left brachial artery and the root of the aorta, reaches the left lung and then across the surface of the oesophagus, divides into dorsal and ventral branches.
• The two dorsal and the two ventral branches of the vagi unite forming the two trunks dorsal and ventral oesophageal continuations of the vagi on the respective faces of the oesophagus, which pass through the diaphragm into the abdominal cavity to supply the abdominal organs.

• The auricular branch from the jugular ganglion enters the facial canal, emerges out at the stylomastoid foramen passes through the foramen in the conchal cartilage and supplies branches to the lining membrane of the external ear.
• The pharyngeal branch along with the pharyngeal branch of glossopharyngeal and the sympathetic fibres form a plexus from which motor fibres are supplied to the pharyngeal constrictors, muscles of soft palate except tensor palati.
• The anterior laryngeal nerve presents at its origin the ganglion nodosum. It arises at about the level of the division of the carotid artery, supplies sensory branches to the mucous membrane of the larynx and an external laryngeal branch for the cricothyroid muscle.
• In the neck, the vagus gives off branches to trachea and oesophagus.
• In the thoracic cavity, the vagus gives off the following branches
  • Cardiac branches to the heart.
  • Pulmonary branches to the lungs.
  • The posterior or recurrent laryngeal nerve: It arises from the vagus at different levels on the two sides. The right is in advance of the left at the posterior border of the first rib, gives off sensory branches to the trachea and oesophagus, leaves the thorax, passes up the neck in the jugular furrow inside the carotid sheath below the common carotid artery and gives off branches to all the laryngeal muscles except the cricothyroid.
  • The left recurrent laryngeal arises at the level of the base of the heart, winds round the right face of the aortic arch, passes forward, gives off sensory branches to the trachea and oesophagus, leaves the thorax, passes in the neck deeply in the jugular furrow along the ventral face of the oesophagus which separates it from the carotid sheath. It reaches the larynx and is distributed to the muscles of the larynx as on the right side.
• In the abdominal cavity, the dorsal and ventral oesophageal trunks are distributed as follows:
• The dorsal trunk gives off
  • Branch accompanying omaso abomasal artery and its divisions and supplies omasum and abomasum.
  • Branches which accompany splenic, right and left ruminal arteries, supply corresponding organs
  • Branches which accompany the divisions of anterior mesenteric artery, supply the small and large intestines except the terminal colon and rectum
  • Branches to kidney.
• The ventral trunk passes on the right face of reticulum and terminates on the parietal surface of the abomasum. It gives off the pyloric branch which passes along the lesser omentum to supply the liver, first and second parts of duodenum and pyloric part of abomasum.