autonomic nervous system
X Vagus nerve (mixed) contains motor fibers which start from nucleus ambiguus, parasympathetic (preganglionic) fibers form dorsal nucleus and sensory fibers from superior and inferior ganglia in jugular foramen.
* Cranial part of vagus nerve gives off the following branches:
Meningeal branch which starts from superior ganglion and passes to cranial dura mater in posterior cranial fossa;
Auricular branch, which starts from superior ganglion
, passes over mastoid canalicule of temporal bone and innervates the skin of external surface of auricle and posterior wall of external acoustic meatus.
The vagus nerve is composed of both motor and sensory fibers, and has a more extensive course and distribution than any of the other cranial nerves, since it passes through the neck and thorax to the abdomen.
The vagus is attached by eight or ten filaments to the medulla oblongata in the groove between the olive and the inferior peduncle, below the glossopharyngeal. The sensory fibers arise from the cells of the jugular ganglion and ganglion nodosum of the nerve, and, when traced into the medulla oblongata mostly end by arborizing around the cells of the inferior part of a nucleus which lies beneath the ala cinerea in the lower part of the rhomboid fossa. These are the sympathetic afferent fibers. Some of the sensory fibers of the glossopharyngeal nerve have been seen to end in the upper part of this nucleus. A few of the sensory fibers of the vagus, probably taste fibers, descend in the fasciculus solitarius and end around its cells. The somatic sensory fibers, few in number, from the posterior part of the external auditory meatus and the back of the ear, probably join the spinal tract of the trigeminal as it descends in the medulla. The somatic motor fibers arise from the cells of the nucleus ambiguus, already referred to in connection with the motor root of the glossopharyngeal nerve.
The sympathetic efferent fibers, distributed probably as preganglionic fibers to the thoracic and abdominal viscera, i. e., as motor fibers to the bronchial tree, inhibitory fibers to the heart, motor fibers to the esophagus, stomach, small intestine and gall passages, and as secretory fibers to the stomach and pancreas, arise from the dorsal nucleus of the vagus.
The filaments of the nerve unite, and form a flat cord, which passes beneath the flocculus to the jugular foramen, through which it leaves the cranium. In emerging through this opening, the vagus is accompanied by and contained in the same sheath of dura mater with the accessory nerve, a septum separating them from the glossopharyngeal which lies in front (792). In this situation the vagus presents a well-marked ganglionic enlargement, which is called the jugular ganglion (ganglion of the root); to it the accessory nerve is connected by one or two filaments. After its exit from the jugular foramen the vagus is joined by the cranial portion of the accessory nerve, and enlarges into a second gangliform swelling, called the ganglion nodosum (ganglion of the trunk); through this the fibers of the cranial portion of the accessory pass without interruption, being principally distributed to the pharyngeal and superior laryngeal branches of the vagus, but some of its fibers descend in the trunk of the vagus, to be distributed with the recurrent nerve and probably also with the cardiac nerves.
The vagus nerve passes vertically down the neck within the carotid sheath, lying between the internal jugular vein and internal carotid artery as far as the upper border of the thyroid cartilage, and then between the same vein and the common carotid artery to the root of the neck. The further course of the nerve differs on the two sides of the body.
On the right side, the nerve passes across the subclavian artery between it and the right innominate vein, and descends by the side of the trachea to the back of the root of the lung, where it spreads out in the posterior pulmonary plexus. From the lower part of this plexus two cords descend on the esophagus, and divide to form, with branches from the opposite nerve, the esophageal plexus. Below, these branches are collected into a single cord, which runs along the back of the esophagus enters the abdomen, and is distributed to the postero-inferior surface of the stomach, joining the left side of the celiac plexus, and sending filaments to the lienal plexus.
On the left side, the vagus enters the thorax between the left carotid and subclavian arteries, behind the left innominate vein. It crosses the left side of the arch of the aorta, and descends behind the root of the left lung, forming there the posterior pulmonary plexus. From this it runs along the anterior surface of the esophagus, where it unites with the nerve of the right side in the esophageal plexus, and is continued to the stomach, distributing branches over its anterosuperior surface; some of these extend over the fundus, and others along the lesser curvature. Filaments from these branches enter the lesser omentum, and join the hepatic plexus.
The Jugular Ganglion (ganglion jugulare; ganglion
of the root) is of a grayish color, spherical in form, about
Branches of Communication.—This ganglion is connected by several delicate filaments to the cranial portion of the accessory nerve; it also communicates by a twig with the petrous ganglion of the glossopharyngeal, with the facial nerve by means of its auricular branch, and with the sympathetic by means of an ascending filament from the superior cervical ganglion.
The Ganglion Nodosum (ganglion of the trunk;
inferior ganglion) is cylindrical in form, of a reddish color, and
Branches of Communication.—This ganglion is connected with the hypoglossal, the superior cervical ganglion of the sympathetic, and the loop between the first and second cervical nerves.
Branches of Distribution.—The branches of distribution of the vagus are:
In the Jugular Fossa…
In the Neck…………
In the Thorax……….
In the Abdomen…….
The Meningeal Branch (ramus meningeus; dural branch) is a recurrent filament given off from the jugular ganglion; it is distributed to the dura mater in the posterior fossa of the base of the skull.
The Auricular Branch (ramus auricularis; nerve of
Arnold) arises from the jugular ganglion, and is joined soon after
its origin by a filament from the petrous ganglion of the glossopharyngeal; it
passes behind the internal jugular vein, and enters the mastoid canaliculus on
the lateral wall of the jugular fossa. Traversing the substance of the temporal
bone, it crosses the facial canal about
The Pharyngeal Branch (ramus pharyngeus), the principal motor nerve of the pharynx, arises from the upper part of the ganglion nodosum, and consists principally of filaments from the cranial portion of the accessory nerve. It passes across the internal carotid artery to the upper border of the Constrictor pharyngis medius, where it divides into numerous filaments, which join with branches from the glossopharyngeal, sympathetic, and external laryngeal to form the pharyngeal plexus. From the plexus, branches are distributed to the muscles and mucous membrane of the pharynx and the muscles of the soft palate, except the Tensor veli palatini. A minute filament descends and joins the hypoglossal nerve as it winds around the occipital artery.
The Superior Laryngeal Nerve (n. laryngeus superior) larger than the preceding, arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic. It descends, by the side of the pharynx, behind the internal carotid artery, and divides into two branches, external and internal.
The external branch (ramus externus), the smaller, descends on the larynx, beneath the Sternothyreoideus, to supply the Cricothyreoideus. It gives branches to the pharyngeal plexus and the Constrictor pharyngis inferior, and communicates with the superior cardiac nerve, behind the common carotid artery.
The internal branch (ramus internus) descends to the hyothyroid membrane, pierces it in company with the superior laryngeal artery, and is distributed to the mucous membrane of the larynx. Of these branches some are distributed to the epiglottis, the base of the tongue, and the epiglottic glands; others pass backward, in the aryepiglottic fold, to supply the mucous membrane surrounding the entrance of the larynx, and that lining the cavity of the larynx as low down as the vocal folds. A filament descends beneath the mucous membrane on the inner surface of the thyroid cartilage and joins the recurrent nerve.
The Recurrent Nerve (n. recurrens; inferior or recurrent laryngeal nerve) arises, on the right side, in front of the subclavian artery; winds from before backward around that vessel, and ascends obliquely to the side of the trachea behind the common carotid artery, and either in front of or behind the inferior thyroid artery. On the left side, it arises on the left of the arch of the aorta, and winds below the aorta at the point where the ligamentum arteriosum is attached, and then ascends to the side of the trachea. The nerve on either side ascends in the groove between the trachea and esophagus, passes under the lower border of the Constrictor pharyngis inferior, and enters the larynx behind the articulation of the inferior cornu of the thyroid cartilage with the cricoid; it is distributed to all the muscles of the larynx, excepting the Cricothyreoideus. It communicates with the internal branch of the superior laryngeal nerve, and gives off a few filaments to the mucous membrane of the lower part of the larynx.
As the recurrent nerve hooks around the subclavian artery or aorta, it gives off several cardiac filaments to the deep part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the esophagus; branches to the mucous membrane and muscular fibers of the trachea; and some pharyngeal filaments to the Constrictor pharyngis inferior.
The Superior Cardiac Branches (rami cardiaci superiores; cervical cardiac branches), two or three in number, arise from the vagus, at the upper and lower parts of the neck.
The upper branches are small, and communicate with the cardiac branches of the sympathetic. They can be traced to the deep part of the cardiac plexus.
The lower branch arises at the root of the neck, just above the first rib. That from the right vagus passes in front or by the side of the innominate artery, and proceeds to the deep part of the cardiac plexus; that from the left runs down across the left side of the arch of the aorta, and joins the superficial part of the cardiac plexus.
* Cervical part of vagus nerve gives off:
Pharyngeal branches with branches of Glossopharyngeal nerve and sympathetic trunk form pharyngeal plexus, that innervates mucous membrane and muscles of the throat (superior and middle constrictors; levator veli palatini, palatopharyngeus and palatoglossus, uvulae muscles).
Superior cervical cardiac branches pass downward along common carotid artery and communicate with sympathetic nerves, enter into cardiac plexus and supply the heart (sensory and parasympathetic innervating).
Superior laryngeal nerve originate from inferior ganglion and carry sensory, motor and parasympathetic preganglionic fibers. Motor fibers of the external branch innervate cricothyroid and inferior constrictor muscles, sensory fibers (internal branch) supply mucous membrane of the larynx over vocal fold, mucous membrane of the epiglottis and tongue root.
Recurrent laryngeal nerve passes upward between esophagus and trachea and sends a numerous twigs. Inferior laryngeal nerve supplies mucous membrane of the larynx below vocal fold and the rest of muscles (thyroarytenoid, lateral and posterior cricoarytenoid, transverse and oblique arytenoid, vocalis). Tracheal, esophageal and inferior cervical cardiac branches supply internal organs.
* Thoracic part of vagus nerve gives off:
Thoracic cardiac branches which pass to cardiac plexus;
Bronchial branches with sympathetic nerves form pulmonary plexus. Last enters in lungs with bronchi.
Esophageal branches form esophageal plexus round this organ.
Abdominal part of vagus nerve is represented by anterior and posterior vagal trunks, which originate from esophageal plexus. Anterior vagal trunk located on front surface of the stomach and gives branches gives off the anterior gastric and hepatic branches. Posterior vagal trunk supplies back gastric wall, and gives off coeliac branches to reach coeliac plexus. Then fibers of vagus nerve with sympathetic fibers supply the liver, spleen, pancreas, kidneys, small and large intestine (including a upper department of descending colon).
Sympathetic centres are located in lateral intermediate nuclei of lateral horns (spinal cord segments C8-Th1-Th12-L1-L2).
Peripheral sympathetic division includes right and left sympathetic trunks, communicating branches, prevertebral sympathetic ganglia, plexuses and fibbers, which pass to organs and tissues.
Sympathetic trunk is a paired formation, which is found on sides from vertebral column and consists of 20-25 paravertebral sympathetic ganglia, joint between each other by interganglionic rami. The white communicating branches from spinal nerves approach to sympathetic trunk They are preganglionic fiber (passes from lateral intermediate nucleus in composition of anterior rootlets and spinal nerve to nearest paravertebral sympathetic ganglion). The white communicating branches pass to eighth cervical, all thoracic and two top lumbar spinal ganglion.
Sympathetic trunk consists of 3 cervical, 10-12 thoracic, 4-5 lumbar, 4-5 sacral and one unpaired coccigeal ganglia. White communicating branches (preganglionic fibers) approach to upper cervical, lower sacral and coccigeal ganglia by the interganglionic branches. Ganglia of sympathetic trunk give off the gray communicating branches, which direct to nearest spinal nerve and contain postganglionic fibers.
Superior cervical ganglion is a largest ganglion of sympathetic trunk, is located in the level of transversal processes of 2-3 cervical vertebrae. Superior cervical ganglion gives off the following branches:
- gray communicating rami for I-IV cervical spinal nerves;
- internal carotid nerve passes to carotid artery and forms internal carotid plexus, which passes into cranial cavity. Sympathetic rootlet for pterygopalatine ganglion (radix sympathica - deep petrosal nerve) separates from internal carotid plexus. Deep petrosal nerve passes through the pterygopalatine canal get the pterygopalatine fossa, transitory passing through the ganglion and realize innervation of the vessels and glands of mucous membrane of the nose cavity and mouth, conjuctive and face skin;
- jugular nerve is passes on wall of internal jugular vein, where divides into branches passing to the 9th, 10th and 11th cranial nerves;
- laryngо-pharyngeі nerves take hand in formation laryngо-pharyngeus plexus, innervating mucous membrane and vessels of the pharynx and larynx;
- superior cervical cardiac nerve passes down parallelly with sympathetic trunk, to deep part of cardiac plexus.
Middle cervical ganglion, inconstant, located anteriorly from transversal process of 6th cervical vertebra. This ganglion is connected with superior and inferior ganglia by interganglionic rami. They form subclavian loop around subclavian artery. Middle cervical ganglion gives off such branches:
- gray communicating branches to V-VI cervical spinal nerves;
- common carotid nerves, which take hand in formation of external carotid plexus and plexus of inferior thyroid artery;
- middle cervical cardiac nerve passes alongside of superior cervical cardiac nerve and enters into deep part of cardiac plexus.
Inferior cervical ganglion frequently flows together with first thoracic ganglion and forms a cervicothoracic ganglion (stellate ganglion). It lies on neck of first rib, behind subclavian artery. Ganglion gives off the following branches:
- gray communicating branches to VI-VIII cervical spinal nerves;
- subclavian nerves, which form subclavian plexus, that ramifies on branches of this artery;
- branches to vagus and phrenic nerves;
- vertebral nerve, which forms vertebral plexus round vertebral artery. This plexus spreads with branches of vertebral artery to spinal cord and brain meninges;
inferior cervical cardiac nerve is passes to deep part of cardiac plexus.
The cephalic portion of the sympathetic system begins as the internal carotid nerve, which appears to be a direct prolongation of the superior cervical ganglion. It is soft in texture, and of a reddish color. It ascends by the side of the internal carotid artery, and, entering the carotid canal in the temporal bone, divides into two branches, which lie one on the lateral and the other on the medial side of that vessel.
The lateral branch, the larger of the two, distributes filaments to the internal carotid artery, and forms the internal carotid plexus.
The medial branch also distributes filaments to the internal carotid artery, and, continuing onward, forms the cavernous plexus.
The internal carotid plexus (plexus caroticus internus; carotid plexus) is situated on the lateral side of the internal carotid artery, and in the plexus there occasionally exists a small gangliform swelling, the carotid ganglion, on the under surface of the artery. The internal carotid plexus communicates with the semilunar ganglion, the abducent nerve, and the sphenopalatine ganglion; it distributes filaments to the wall of the carotid artery, and also communicates with the tympanic branch of the glossopharyngeal nerve.
The communicating branches with the abducent nerve consist of one or two filaments which join that nerve as it lies upon the lateral side of the internal carotid artery. The communication with the sphenopalatine ganglion is effected by a branch, the deep petrosal, given off from the plexus on the lateral side of the artery; this branch passes through the cartilage filling up the foramen lacerum, and joins the greater superficial petrosal to form the nerve of the pterygoid canal (Vidian nerve), which passes through the pterygoid canal to the sphenopalatine ganglion. The communication with the tympanic branch of the glossopharyngeal nerve is effected by the caroticotympanic, which may consist of two or three delicate filaments.
The cavernous plexus (plexus cavernosus) is situated below and medial to that part of the internal carotid artery which is placed by the side of the sella turcica in the cavernous sinus, and is formed chiefly by the medial division of the internal carotid nerve. It communicates with the oculomotor, the trochlear, the ophthalmic and the abducent nerves, and with the ciliary ganglion, and distributes filaments to the wall of the internal carotid artery. The branch of communication with the oculomotor nerve joins that nerve at its point of division; the branch to the trochlear nerve joins it as it lies on the lateral wall of the cavernous sinus; other filaments are connected with the under surface of the ophthalmic nerve; and a second filament joins the abducent nerve.
The filaments of connection with the ciliary ganglion arise from the anterior part of the cavernous plexus and enter the orbit through the superior orbital fissure; they may join the nasociliary branch of the ophthalmic nerve, or be continued forward as a separate branch.
The terminal filaments from the internal carotid and cavernous plexuses are prolonged as plexuses around the anterior and middle cerebral arteries and the ophthalmic artery; along the former vessels, they may be traced to the pia mater; along the latter, into the orbit, where they accompany each of the branches of the vessel. The filaments prolonged on to the anterior communicating artery connect the sympathetic nerves of the right and left sides.
The cervical portion of the sympathetic trunk consists of three ganglia, distinguished, according to their positions, as the superior, middle, and inferior ganglia, connected by intervening cords. This portion receives no white rami communicantes from the cervical spinal nerves; its spinal fibers are derived from the white rami of the upper thoracic nerves, and enter the corresponding thoracic ganglia of the sympathetic trunk, through which they ascend into the neck.
The superior cervical ganglion (ganglion cervicale superius), the largest of the three, is placed opposite the second and third cervical vertebræ. It is of a reddishgray color, and usually fusiform in shape; sometimes broad and flattened, and occasionally constricted at intervals; it is believed to be formed by the coalescence of four ganglia, corresponding to the upper four cervical nerves. It is in relation, in front, with the sheath of the internal carotid artery and internal jugular vein; behind, with the Longus capitis muscle.
Its branches may be divided into inferior, lateral, medial, and anterior.
The Inferior Branch communicates with the middle cervical ganglion.
The Lateral Branches (external branches) consist of gray rami communicantes to the upper four cervical nerves and to certain of the cranial nerves. Sometimes the branch to the fourth cervical nerve may come from the trunk connecting the upper and middle cervical ganglia. The branches to the cranial nerves consist of delicate filaments, which run to the ganglion nodosum of the vagus, and to the hypoglossal nerve. A filament, the jugular nerve, passes upward to the base of the skull, and divides to join the petrous ganglion of the glossopharyngeal, and the jugular ganglion of the vagus.
The Medial Branches (internal branches) are peripheral, and are the larnygopharyngeal branches and the superior cardiac nerve.
The laryngopharyngeal branches (rami laryngopharyngei) pass to the side of the pharynx, where they join with branches from the glossopharyngeal, vagus, and external laryngeal nerves to form the pharyngeal plexus.
The superior cardiac nerve (n. cardiacus superior) arises by two or more branches from the superior cervical ganglion, and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the neck behind the common carotid artery, and in front of the Longus colli muscle; and crosses in front of the inferior thyroid artery, and recurrent nerve. The course of the nerves on the two sides then differ. The right nerve, at the root of the neck, passes either in front of or behind the subclavian artery, and along the innominate artery to the back of the arch of the aorta, where it joins the deep part of the cardiac plexus. It is connected with other branches of the sympathetic; about the middle of the neck it receives filaments from the external laryngeal nerve; lower down, one or two twigs from the vagus; and as it enters the thorax it is joined by a filament from the recurrent nerve. Filaments from the nerve communicate with the thyroid branches from the middle cervical ganglion. The left nerve, in the thorax, runs in front of the left common carotid artery and across the left side of the arch of the aorta, to the superficial part of the cardiac plexus.
The Anterior Branches (nn. carotici externi) ramify upon the common carotid artery and upon the external carotid artery and its branches, forming around each a delicate plexus, on the nerves composing which small ganglia are occasionally found. The plexuses accompanying some of these arteries have important communications with other nerves. That surrounding the external maxillary artery communicates with the submaxillary ganglion by a filament; and that accompanying the middle meningeal artery sends an offset to the otic ganglion, and a second, the external petrosal nerve, to the genicular ganglion of the facial nerve.
The middle cervical ganglion (ganglion cervicale medium) is the smallest of the three cervical ganglia, and is occasionally wanting. It is placed opposite the sixth cervical vertebra, usually in front of, or close to, the inferior thyroid artery. It is probably formed by the coalescence of two ganglia corresponding to the fifth and sixth cervical nerves.
It sends gray rami communicantes to the fifth and sixth cervical nerves, and gives off the middle cardiac nerve.
The Middle Cardiac Nerve (n. cardiacus medius; great cardiac nerve), the largest of the three cardiac nerves, arises from the middle cervical ganglion, or from the trunk between the middle and inferior ganglia. On the right side it descends behind the common carotid artery, and at the root of the neck runs either in front of or behind the subclavian artery; it then descends on the trachea, receives a few filaments from the recurrent nerve, and joins the right half of the deep part of the cardiac plexus. In the neck, it communicates with the superior cardiac and recurrent nerves. On the left side, the middle cardiac nerve enters the chest between the left carotid and subclavian arteries, and joins the left half of the deep part of the cardiac plexus.
The inferior cervical ganglion (ganglion cervicale inferius) is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery. Its form is irregular; it is larger in size than the preceding, and is frequently fused with the first thoracic ganglion. It is probably formed by the coalescence of two ganglia which correspond to the seventh and eighth cervical nerves. It is connected to the middle cervical ganglion by two or more cords, one of which forms a loop around the subclavian artery and supplies offsets to it. This loop is named the ansa subclavia (Vieussenii).
The ganglion sends gray rami communicantes to the seventh and eighth cervical nerves.
It gives off the inferior cardiac nerve, and offsets to bloodvessels.
The inferior cardiac nerve (n. cardiacus inferior) arises from either the inferior cervical or the first thoracic ganglion. It descends behind the subclavian artery and along the front of the trachea, to join the deep part of the cardiac plexus. It communicates freely behind the subclavian artery with the recurrent nerve and the middle cardiac nerve.
The offsets to bloodvessels form plexuses on the subclavian artery and its branches. The plexus on the vertebral artery is continued on to the basilar, posterior cerebral, and cerebellar arteries. The plexus on the inferior thyroid artery accompanies the artery to the thyroid gland, and communicates with the recurrent and external laryngeal nerves, with the superior cardiac nerve, and with the plexus on the common carotid artery.