6. Gross Anatomy
Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific
nerves include several cranial nerves, specifically the oculomotor nerve, facial
nerve, glossopharyngeal nerve, and vagus nerve.
The vagus nerve has the longest course of all the cranial nerves, extending from the head to the
abdomen. Its name is derived from the Latin ‘vagary’ – meaning wandering. It is sometimes referred
to as the wandering nerve.
It originates from Medulla Oblongata. It contains motor and sensory fibers and, because it passes
through the neck and thorax to the abdomen, has the widest distribution in the body. It contains
somatic and visceral afferent fibers, as well as general and special visceral efferent fibers.
7. Fibres
General visceral efferent( GVE): provides parasympathetic innervations to glands of mucous
membranes of the pharynx, larynx, organs in the neck, thorax and abdomen.
Special visceral efferent (SVE): innervates skeletal muscles of the pharynx and larynx.
General somatic afferent(GSA): carries sensation from the external auditory meatus and
tympanic membrane.
General visceral afferent(GVA): carries information from the thoracic and abdominal viscera;
aortic body and arch.
Special visceral afferent(SVA): carries taste of the epiglottis region of the tongue.
8. Distribution
In Head: The vagus nerve originates from the medulla of the brainstem. It exits the cranium via the
jugular foramen, with the glossopharyngeal and accessory nerves (CN IX and XI respectively).
Within the cranium, the auricular branch arises. This supplies sensation to the posterior part of the
external auditory canal and external ear.
9. In Neck
The vagus nerve passes into the carotid sheath, travelling inferiorly with the internal jugular vein and common
carotid artery. At the base of the neck, the right and left nerves have differing pathways
10. The right vagus nerve passes anterior to the subclavian artery
and posterior to the sternoclavicular joint, entering the thorax.
The left vagus nerve passes inferiorly between the left
common carotid and left subclavian arteries, posterior to the
sternoclavicular joint, entering the thorax.
11. Several branches arise in the neck:
Pharyngeal branches – Provides motor
innervation to the majority of the muscles of the
pharynx and soft palate.
Superior laryngeal nerve – Splits into internal
and external branches. The external laryngeal
nerve innervates the cricothyroid muscle of the
larynx. The internal laryngeal provides sensory
innervation to the laryngopharynx and superior
part of the larynx.
Recurrent laryngeal nerve (right side only) –
Hooks underneath the right sub-clavian artery,
then ascends towards to the larynx. It innervates
the majority of the intrinsic muscles of the larynx.
12. In Thorax
In the thorax, the right vagus nerve forms the
posterior vagal trunk, and the left forms the
anterior vagal trunk. Branches from the vagal
trunks contribute to the formation of the
oesophageal plexus, which innervates the smooth
muscle of the oesophagus.
Two other branches arise in the thorax:
Left recurrent laryngeal nerve – it hooks under
the arch of the aorta, ascending to innervate the
majority of the intrinsic muscles of the larynx.
Cardiac branches – these innervate regulate
heart rate and provide visceral sensation to the
organ.
The vagal trunks enter the abdomen via the
oesophageal hiatus, an opening in the diaphragm.
13. In Abdomen
In the abdomen, the vagal trunks terminate by dividing into branches that supply the oesophagus,
stomach and the small and large bowel (up to the splenic flexure).
14. Organs innervating
Organ Nerves
Stomach PS: anterior and posterior vagal trunks
S: greater splanchnic nerves
Duodenum PS: vagus nerves
S: greater splanchnic nerves
Jejunum and ileum PS: posterior vagal trunks
S: greater splanchnic nerves
Gallbladder and liver PS: vagus nerve
S: celiac plexus
right phrenic nerve
Colon PS: vagus nerves and pelvic splanchnic nerves
S: lesser and least splanchnic nerves
Pancreatic head PS: vagus nerves
S: thoracic splanchnic nerves
Kidneys and ureters PS: vagus nerve
S: thoracic and lumbar splanchnic nerves
15. Effects of Vagus Nerve
Sensory : from throat, heart, lungs, and abdomen.
Special sensory: Provides taste sensation behind the tongue.
Motor: Provides movement functions for the muscles in the neck responsible for swallowing
and speech.
Parasympathetic: Responsible for the digestive tract, respiration, and heart rate
functioning. The vagus nerve also helps with defecation, urination, and sexual arousal.
16. Communication between the brain and the gut: vagus delivers information from the gut to
the brain.
Relaxation with deep breathing: vagus nerve communicates with the diaphragm. With deep
breaths, a person feels more relaxed.
Lowering the heart rate and blood pressure: if the vagus nerve is overactive, it can lead to
heart being unable to pump enough blood around the body. In some cases, excessive vagus
nerve activity can cause loss of consciousness and organ damage.
Fear management: vagus nerve sends information from gut to the brain, which is linked to
dealing with stress, anxiety, and fear- hence the saying ”gut feeling”. These signals help a
person to recover from stressful and scary situations.
17. Sensory functions
The sensory functions of the vagus nerve are divided into two components:
Somatic components. These are sensations felt on the skin or in the muscles.
Visceral components. These are sensations felt in the organs of the body.
Laryngopharynx – via the internal laryngeal nerve.
Superior aspect of larynx (above vocal folds) – via the internal laryngeal nerve.
Heart – via cardiac branches of the vagus nerve.
Gastro-intestinal tract (up to the splenic flexure) – via the terminal branches of the vagus
nerve.
18. Motor functions
The vagus nerve innervates the
majority of the muscles associated
with the pharynx and larynx. These
muscles are responsible for the
initiation of swallowing and phonation.
Pharynx
Most of the muscles of the pharynx
are innervated by the pharyngeal
branches of the vagus nerve:
Superior, middle and inferior
pharyngeal constrictor muscles
Stylopharyngeus
19. Larynx: Innervations' to the intrinsic muscles of the
larynx is achieved via the recurrent laryngeal
nerve and external branch of the superior laryngeal
nerve.
Recurrent laryngeal nerve:
• Thyro-arytenoid
• Posterior crico-arytenoid
• Lateral crico-arytenoid
• Transverse and oblique arytenoids
• Vocalis
External laryngeal nerve: Cricothyroid
Other Muscles: In addition to the pharynx and larynx,
the vagus nerve also innervates the palatoglossus of
the tongue, and the majority of the muscles of the soft
palate.
20. Parasympathetic function
In the thorax and abdomen, the vagus nerve is
the main parasympathetic outflow to the heart
and gastro-intestinal organs.
The Heart
Cardiac branches arise in the thorax,
conveying parasympathetic innervations to the
sino-atrial and atrio-ventricular nodes of the
heart.
21. Gastro-Intestinal System
The vagus nerve provides parasympathetic innervation to the majority of the abdominal
organs. It sends branches to the oesophagus, stomach and most of the intestinal tract –
up to the splenic flexure of the large colon.
The function of the vagus nerve is to stimulate smooth muscle contraction and glandular
secretions in these organs. For example, in the stomach, the vagus nerve increases the
rate of gastric emptying, and stimulates acid production.
22. Vagus Indigestion (Hoflund syndrome)
It is a chronic unusual type of indigestion manifested by in coordinated
contractions of rumen. It is an infrequent clinical problem of both cattle and
buffaloes. It is very difficult to diagnose the case clinically as there is no clear-cut
manifestation.
Stimulates the profile of traumatic reticulo-peritonitis at the initial stage.
Noticeable symptoms: Constipation
Prognosis: poor.
23. Aetiology
Traumatic reticulo peritonitis.
Adhesions between rumen and abomasums.
Inflammation of reticular wall damaging stretch receptors.
Any affection interfering with esophageal groove reflexes.
Enlarged mediastinal lymph nodes exerting pressure on vagus nerve.
Diaphragmatic hernia.
Chronic pleurisy.
Peritonitis due to perforating abomasal ulcer
24. Types
Type 1 vagus indigestion: failure of eructation, and results in free gas bloat and ruminal distention.
Chronic pneumonia or a localized peritonitis following hardware disease of the vagus nerve cranial to
the cardia. Mechanical factors not related to vagus nerve damage that cause esophageal obstruction
may also cause failure of eructation. Other potential cause is pharyngeal trauma, which affects a
more proximal part of the vagus nerve, and esophageal compression by abscesses or neoplasia,
such as lymphosarcoma.
Type 2 vagus indigestion : failure of omasal transport. The rumen becomes distended with feed.
Functional disturbances in omasal motility are the result of vagus nerve damage from inflammation
due to conditions such as mycotic omasitis, reticular abscesses and localized adhesions. The
reticulo-omasal orifice can be mechanically obstructed by an ingested placenta, papillomas or
lymphosarcoma.
25. Type 3 vagus digestion: result of primary or secondary abomasal impaction. Primary impaction
occurs when animals are fed dry, coarse feed with limited water. Secondary impaction is the result
of disturbances in abomasal motility or pyloric outflow failure. Altered motility following an episode
of traumatic reticulo peritonitis is common.
26. Ischemia of the vagus nerve as a sequel to right abomasal torsion also may
occur. Mechanical obstruction or neurogenic dysfunction at the level of the
pylorus can occur with lympho-sarcoma.
Type 4 vagus indigestion: partial fore stomach obstruction, more common
in late pregnancy. During advanced pregnancy, the enlarged uterus
displaces the abomasum cranially which physically interferes with normal
motility.
27. Pathogenesis
Omasal transport failure:
• Atony of the reticulo rumen is often recurrent chronic bloat, or
• There may be hyper motility of the rumen.
• Omasal transport failure associated with ruminal hypermotility : there is gradual
accumulation of ingesta in the rumen and reticulum causing distention but omasum and
abomasums are relatively empty. Animal looks apparently healthy with gross distension
of the rumen. Characteristic contour of the abdomen thus produces is called “Apple”
shaped abdomen. Because the left abdomen is distended and assume the appearance
of an apple whereas the right side assumes the contour of a “pear”.
28. • The decreased rate of evacuation of ingesta produces characteristic grassy and
pasty feces. Animal continue to drink water but there is decreased absorption of
fluid from rumen. On deep palpation, vigorous contraction of the rumen can be
felt in the left paralumbar fossa. In some cases, there is complete atony due to
reticulo-omasal paralysis.
Pyloric outflow failure:
• Pyloric outflow failure leads to accumulation of the ingesta in the abomasums
and omasum. Eventually there is gross distention of rumen and reticulum.
Failure of the ingesta to flow into the intestinal tract combined with sequestration
of the chloride rich fluid into the stomach produce marked dehydration and hypo-
chloremic metabolic alkalosis.
29. Clinical Findings
Atony of rumen with distended abdomen.
Apple shaped abdomen .
Increased rumen motility with foam.
Moderate to severe tympany.
Scanty pasty feces (constipation).
Rustling or gargling sound from omasum.
Accumulation of impacted food in rumen and reticulum.
Slow heart rate: Systolic murmurs.
Sunken eyes, dehydration.
Sudden drop in milk yield.
Hyperacidity in abomasums will cause irritation of the mucosa later on ulceration and bleeding.
Complete depression, anemia and recumbency stimulating downer cow syndrome.
Non-responsive to treatment.
Collapse, coma and death.
30. Ruminal distension with hypermotility (Type 1): gaseous distension of rumen. Animal remains in
off fed condition. Left and right flank ballotment show fluid splashing sound. The feces are scanty
and pasty. Heart rate may be decreased (bradycardia). Rectal examination reveals distension of
rumen. Enlarged rumen when viewed from rear angle looks L-shaped. Right flank remain distended
only in the lower half- assuming apple shaped abdomen.
31. Ruminal distension with atony (Type 2): usually observed in late pregnancy and continues to exist
even following calving. Such case always show normal picture except the problem like off fed
condition, scanty feces and obvious distension of abdomen. They seldom show response to
purgatives or para-sympathomimetic drugs. Bloat used to persist. Fluid splashing sound may be
observed.
Pyloric obstruction and abomasal impaction (Type 3): abomasal impaction is mostly noted in
the later part of gestation. Clinical signs include anorexia and scanty feces. Rumen motility is
absent. The impacted abomasums can be felt in the lower right abdomen having doughy feeling.
Finally, the animal becomes weal and recumbent. Die due to dehydration, electrolyte and acid-base
imbalance. Occasionally, impacted abomasums may rupture causing eventual death.
32. Diagnosis
Left abomasal displacement: history of
calving; develop following calving;
chronic indigestion; constipation;
abomasal sound on auscultation at left
lower flank; contracted abdomen.
Right abomasal displacement:
displaced abomasums can be palpated;
it fills up almost entire right half of the
abdominal cavity.
33. Intestinal obstruction: faecolith; lipoma of fat necrosis can be felt through rectal palpation as hard
mass. This interferes the process of defecation.
Diaphragmatic hernia: ventral thorax on auscultation will reveal splashing reticular sound.
Radiograph will show disruption in the continuity of the diaphragm with reticular shadows
extending into thoracic cavity.
Diffuse peritonitis: abdominal distension, febrile reaction, short course.
Omental bursitis: rumen is small; abdomenocentesis will reveal thick pus from the omental bursa.
X-ray may be done to explore the condition.
Exploratory laparotomy may be required to determine the etiology.
34. Atropine Test
Diagnosis can be tentatively made based on abdominal distension along with ruminal
hyperactivity and bradycardia. Bradycardia can be considered as diagnostic facet for
vagal indigestion. For this, animal has to be given 30 mg atropine sulphate
subcutaneously and heart beat has to be monitored for every 5 minutes for 20 minutes.
Heart Beat Condition/ Disease
5% or less increase Intracardial lesion
7-16% increase Vagotonic bradycardia
More than 16% increase Vagal indigestion
35. Treatment
Administration of liquid paraffin 2.5 liters orally for 3 to 5 days.
Use of dioctyl sodium sulfosuccinate orally.
Injection vitamin B1 (500mg) daily through intramuscular route.
Use of parasympathetic drugs e.g. Neostigmine hydrochloride.
Infusion of magnesium sulphate into the abomasums.
5% Dextrose saline 2 to 5 litres daily through intravenous drip till recovery. Vitamin B complex may be added
to it.
Subcutaneous calcium gluconate.
Betamethasone or Dexamethasone preparations 4-10 ml through intramuscular route for 23 days.
Rumen fistula.
Rumenotomy and evacuation of rumen contents followed by cud transplantation and symptomatic treatment
with ruminotorics, calcium and potassium solutions.
36. Treatment of Type 1 vagus indigestion: relieve free gas accumulation. (Diagnosis and removal of
any possible esophageal foreign bodies should proceed surgery).
Treatment of early case of Type 2 vagus indigestion : Fluids, electrolytes, rumen cathartics,
access to water and exercise are important. Subcutaneous administration of calcium boroglocunate
may be indicated. A left paralumbar fossaceliotomy and rumenotomy.
Type 3 vagus indigestion: Intravenous fluid administration can be used to correct these
abnormalities. A left paralumbar fossaceliotomy and rumenotomy. Severe cases of abomasal
impaction may require an abomasotomy via a right paracostal approach, but affected animals have
a poor prognosis.
Type 4 vagus indigestion: treated with fluids, electrolytes and calcium. A rumenotomy using a left
paralumbar fossa approach can be utilized to detect and treat underlying disease processes.
37. Prevention
The most common cause of vagal indigestion syndrome is traumatic reticulo-peritonitis,
which causes adhesions and abscesses that interfere with both reticular motility and the
appropriate stratification of feed particles for passage through the abomasum. Therefore,
prevention of traumatic reticulo-peritonitis is important.
Good management practices may prevent some cases of vagal indigestion associated
with chronic pneumonia.
38. References
Text book of clinical veterinary medicine by Prof. Amalendu Chakarbarti
MSD Veterinary Manual
Fall 1996 Newsletter by Joel Russo, Diagnostic Pathology Clerk
Wikipedia
