📝 STANDARD DESCRIPTION:
Course:
- Right and Left vagus enter thorax along the trachea.
- Each gives off the Recurrent Laryngeal Nerve at the base of heart.
- Each vagus then splits into Dorsal & Ventral branches at the level of bronchi.
- Right & left dorsal branches join → Dorsal Vagal Trunk.
- Right & left ventral branches join → Ventral Vagal Trunk.
- Both trunks pass through the OESOPHAGEAL HIATUS into the abdomen.
Supply (parasympathetic):
- Heart (slows rate)
- Lungs / Bronchi (constricts airways)
- Oesophagus
- All abdominal viscera up to about 2/3 of transverse colon.
📚 DETAILED DESCRIPTION:
THE WANDERING NERVE IN THE CHEST
The vagus (CN X) is the longest cranial nerve. After leaving the head and travelling down the neck inside the carotid sheath, both right and left vagi enter the thorax beside the trachea.
STAGE 1 — At the heart base:
Each vagus gives off its recurrent laryngeal nerve, which loops underneath a big artery and runs back up to the larynx (see separate entry).
STAGE 2 — At the lung roots (hilus):
Each vagus sends small branches to the cardiac plexus (around the heart) and the pulmonary plexus (around the bronchi). Then the vagus itself splits into a dorsal and a ventral branch.
STAGE 3 — Formation of vagal trunks:
The dorsal branch of the right vagus joins the dorsal branch of the left vagus to form the Dorsal Vagal Trunk. Similarly, the two ventral branches form the Ventral Vagal Trunk. These two trunks lie on top and bottom of the oesophagus.
STAGE 4 — Exit to abdomen:
Both trunks travel with the oesophagus through the oesophageal hiatus of the diaphragm and reach the rumen and other abdominal organs.
PARASYMPATHETIC ACTIONS in thorax:
• Heart: SLOWS the rate (opposite of sympathetic).
• Bronchi: CONSTRICTS smooth muscle, increases mucus secretion.
• Oesophagus: Drives swallowing waves.
• In ruminants the abdominal vagal supply is especially important for forestomach motility (rumen contractions).
// COMPARATIVE ANALYSIS
| HORSE |
Vagal trunks well defined on the oesophagus. |
| RUMINANT |
Vagal Indigestion (Hoflund's syndrome) — damage to vagal branches around reticulum/abomasum causes failure of forestomach motility. |
| DOG |
Vagal arrhythmias common — strong vagal tone normally slows heart rate during expiration. |
CLINICAL RELEVANCE
Vagal indigestion in cattle: Hardware disease (a swallowed nail/wire piercing the reticulum) damages the ventral vagal branches → rumen stops moving → progressive bloat and weight loss.
