The anterior vagal trunk is a nerve branch of the vagus nerve involved in parasympathetic innervation of the stomach and liver. Thus, the visceromotor fibers of the nerve control portions of involuntary organ activity. Failure of the anterior vagal trunk leads to dysregulation of the liver and stomach.
What is the anterior vagal trunk?
The vagus nerve corresponds to the tenth cranial nerve and also the largest nerve of the parasympathetic nervous system. Its branches are involved in the regulation of nearly all internal organ activities, which is how the nerve got its name in the first place. Literally translated, vagus nerve means “wandering nerve”. The truncus vagalis anterior is a ramus of the vagus nerve. The nerve branch originates in the esophageal plexus, the nerve plexus of the esophagus between the thoracic inlet and the diaphragmatic passage. The plexus, along with the vagus, gives off many fibers to the esophagus, then passes into the gastric plexus and is connected to the cardiac plexus. The anterior vagal trunk contains rami gastrici anteriores and rami hepatici, which are part of the left portion of the vagus nerve. The vagus nerve carries general-somatosensory, general-visceromotor, and special-visceromotor fibers in addition to general-viscerosensory and special-viscerosensory fibers.
Anatomy and structure
Like the vagus nerve, the anterior vagal truncus carries parasympathetic nerve fibers that arise from the dorsal nucleus nervi vagi, or posterior nucleus of the vagus nerve, in the medulla oblongata region. The nucleus dorsalis nervi vagi, and thus nucleus of the truncus vagalis anterior, is a cranial nerve nucleus of the brainstem and also a parasympathetically important nucleus area. The nucleus is composed of motor neurons of relatively small size. Due to their small size, their axons do not directly reach the region to be innervated, but are connected to an additional neuron in the ganglia. The nucleus is composed of general-visceromotor fibers. The nucleus area is controlled by afferent sensory fibers from the nucleus tractus solitarii and hypothalamus. The anterior vagal trunk contains primary fibers from the left vagus nerve due to gastric torsion during embryonic development and gives off two branches itself. The rami gastrici anteriores run to the anterior surface of the stomach and also innervate the small curvature. The rami hepatici of the truncus vagalis anterior run to the liver, where they form the plexus hepaticus or plexus of hepatic nerves. The plexus gives off the ramus pyloricus to the gastric pylorus.
Function and Tasks
The vagus nerve influences the thoracic as well as abdominal organs parasympathetically. The parasympathetic innervation of the organs belongs to the autonomic innervation. This nervous system, unlike the central or peripheral nervous system, is considered an autonomic nervous system. Autonomy implies that the autonomic nervous system regulates and adapts biologically determined, automatically occurring processes of the inner-body realm without being consciously perceived or volitionally influenced by the human being. The truncus vagalis anterior contains specifically general visceromotor fibers and thus enables the contraction of the involuntary musculature, in the narrower sense the movements of the viscera. The motor function of the innervated organs takes place via visceroefferent signals. For example, the truncus vagalis anterior with its rami gastrici anteriores is responsible for the motor function of the anterior surface of the stomach and the small curvature. It also controls the activity of the liver with the hepatic plexus and the actions of the gastric portal with the ramus pyloricus. Like all autonomic nerve fibers, those of the truncus vagalis anterior are mandatory for survival. The vagus nerve supplies visceromotor fibers to both smooth and striated muscle, making it one of the most crucial nerves for human organ activity. In the medulla oblongata and medulla spinalis lies the nucleus spinalis nervi trigemini as the nerve nucleus for the general-somatosensory fiber portions of the vagus nerve. The general-visceromotor fibers originate in the dorsal nucleus nervi vagi of the medulla oblongata. The nucleus of the special-visceromotor vagus fibers is the nucleus ambiguus of the medulla oblongata. The general and special viscerosensitive fibers arise from the nucleus tractus solitarii.
Diseases
When the vagus nerve is compressed, anterior truncus vagalis disorders present along with many other nerve disorders. The vagus nerve is at some anatomic risk of compression when there is a malalignment of the atlas or first cervical vertebra. Thus, because of its proximity to the atlas, the vagus nerve can become entrapped when this vertebra is malpositioned. Depending on how the atlas is misaligned, there may be pressure or irritation of the nerve that affects its functionality. This usually results in vagus nerve symptoms. In addition to nausea, stomach acidity and dizziness, vagus compression may be symptomatic as facial flushing, rapid heartbeat, neck stiffness or pain, or headache. In addition, symptoms such as difficulty swallowing, excessive sweating, more or less severe sleep disturbances, irregular heartbeat, chronic persistent constipation, diarrhea, and thyroid problems may be due to nerve compression. Primary diseases in the autonomic nervous system are rarely seen. Damage to autonomic nerves is usually due to mechanical trauma. Most commonly, such nerve damage is preceded by spinal cord injury. Indeed, the fibers of the autonomic nervous system travel to their target organs via the spinal cord. In addition to traumatic spinal cord lesions, spinal cord infarctions or tumors in the spinal cord are also conceivable causes of functional impairment of the autonomic nervous system. Complete failure of the autonomic nervous system is rarely observed. However, because the parasympathetic and sympathetic nervous systems are antagonists and regulate each other interactively, failure of even one of the fiber qualities leads to severe organ dysfunction.