Innervation of Esophagus
The esophagus is innervated by the vagus nerve as well as several
sympathetic nerves. The vagus nerve innervates the glands and muscles of the
esophagus, and the sympathetic input primarily innervates the capillary
sphincters associated with the organ’s blood supply.
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Nerves
of esophagus
The vagus nerve conveys both motor
and sensory fibers between the nuclei of the medulla oblongata and esophagus.
Like the pharynx, the skeletal muscle of the upper esophagus is voluntary and
the axons that innervate these fibers arise primarily from nerve cell bodies in
the nucleus ambiguus. However, the amount of smooth muscle within the
muscularis externa of the esophagus becomes more pronounced as one moves
inferiorly and it is primarily innervated by axons from the dorsal vagal
motor nucleus.
In the neck, where skeletal muscle
predominates, the esophagus receives somatomotor axons from the recurrent
laryngeal nerves that run superiorly between the esophagus and trachea. On
the right side the recurrent laryngeal nerve arises from the vagus nerve at the
root of the neck and turns superiorly bypassing inferior to the right
subclavian artery before ascending. The left recurrent laryngeal nerve arises
from the left vagus nerve opposite the aortic arch and curves beneath the arch
of the aorta to reach the groove between the trachea and esophagus. Some
inconstant filaments pass to the esophagus from the main vagus nerves that lie in
the carotid sheath behind and between the common carotid artery and internal
jugular vein.
In the thorax, the esophagus
receives filaments from the left recurrent laryngeal nerve and both vagus
nerves. The vagus nerves descend posterior to the bronchi, giving off branches
that unite with axons from the sympathetic trunk to form the smaller anterior
and larger posterior pulmonary plexuses. Below the bronchi each vagus nerve
usually splits into two to four branches, which apply themselves to the surface
of the esophagus in the posterior mediastinum.
The branches from the right and left vagus nerves rotate posteriorly and
anteriorly (respectively) as they divide and reunite to form an openmeshed esophageal
plexus containing small ganglia. At a variable distance above the
esophageal hiatus in the diaphragm, the meshes of the plexus become
reconstituted into an anterior vagal trunk and posterior vagal trunk, embedded
in the anterior and posterior wall of the lowest part of the esophageal wall.
Offshoots from the esophageal plexus and from the anterior and posterior
vagal trunks sink into the esophageal wall. Common variations in the plexus
and in the vagal trunks are of especial significance to anyone performing
vagotomy, and the surgeon should remember that there may be more than
one anterior or posterior vagal trunk. The vagus nerves and their resultant
trunks interdigitate with filaments from the sympathetic trunks so that, from
the neck downward, they are really mixed parasympatheticsympathetic plexuses.
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Intrinsic
nerves and variations in nerves of esophagus
Sympathetic Supply
The sympathetic preganglionic
fibers are the axons that originate in the intermediolateral cell column,
located mainly in the fourth to sixth thoracic segments
of the spinal cord. These presynaptic axons emerge in the anterior spinal nerve
roots corresponding to the segments containing their parent cells. They leave
the spinal nerves via white rami communicans and pass to the ganglionic
nerve cell bodies located in the sympathetic trunk. Some fibers form
synapses with cells in the mid thoracic ganglia, but others pass to higher and
lower ganglia in the trunk before synapsing. Postsynaptic axons exiting the
sympathetic trunk reach the esophagus through branches from the sympathetic
trunks. The afferent impulses are conveyed in fibers that pursue an
antiparallel route, but they do not relay in the sympathetic trunk. Instead
they pass through the trunk without synapsing, travel through the white rami
communicans to reach the spinal nerve, and then travel along the posterior
nerve roots before reaching the posterior horn of the spinal cord. Their
pseudounipolar nerve cell bodies are located in the posterior (dorsal) root
ganglia.
The uppermost part of the esophagus
is supplied by offshoots from the pharyngeal plexus that contain postsynaptic
sympathetic axons. More inferiorly, it receives axons from the cardiac branches
of the superior cervical ganglia and occasionally from the middle
cervical or vertebral ganglion of the sympathetic trunk. Other
fibers reach the esophagus in the delicate nerve plexuses accompanying the
arteries that supply it. In the upper thorax, esophageal axons are supplied by
the stellate ganglia or ansa subclavia, and the delicate thoracic
cardiac nerves are often associated with fibers for the esophagus, trachea,
aorta, and pulmonary structures.
In the lower thorax, axons pass
from the greater (thoracic) splanchnic nerves to the nearby esophageal
plexus. The greater splanchnic nerves generally arise by three or
four larger roots and an inconstant number of smaller rootlets from the fifth
to the ninth thoracic ganglia of the sympathetic trunk, although there is significant
variation. The roots and rootlets pass obliquely anteriorly, medially, and
inferiorly across the sides of the thoracic vertebral bodies and intervertebral
disks and coalesce to form a nerve of considerable size. On each side the nerve
enters the abdomen by piercing the homolateral diaphragmatic crus or, less
often, by passing between the lateral margins of the
crura and the fibers arising from the medial arcuate ligament. The
intraabdominal course is short, and each nerve breaks up into branches that end
mainly in the celiac ganglion. The lesser and least thoracic splanchnic nerves
terminate mainly in the aorticorenal and superior mesenteric ganglia. Filaments
from the terminal part of the left greater splanchnic nerve reach the abdominal
part of the esophagus.
