The Sympathetic Ganglia of the Head and Their Associations with the Cranial Nerves
The sympathetic system of the head, like that of the remainder of the body described below, is arranged in the form of a continuous gangHated plexus subdivided into sub-plexuses.
Unlike the great unpaired prevertebral plexuses in the thoracic and abdominal cavities, all the larger sympathetic ganglia of the head are paired, gangha corresponding to each other being found on either side. Thus they may be considered as an upward extension of the series of paired lumbar, thoracic and cervical ganglia belonging to the sympathetic trunks lying along either side of the vertebral column. Numerous small ganglia, many of them microscopic, occur in the sub-plexuses throughout the head. These are irregular in size and position and those in the region of the median line are no doubt unpaired.
In origin, the ganglia of the cephalic plexus consist of cell-bodies which, in the early stages of development, migrated from the fundaments of the ganglia of the vagus, glosso-pharyngeal and glosso-palatine nerves, and most especially from that of the semilunar (Gasserian) ganglion of the trigeminus - a developmental relation identical with that of the remainder of the sympathetic system to the ganglia of the spinal nerves. Just as is known for the spina! ganglia, some cell-bodies destined to develop into sympathetic neurones, instead of migrating, remained within the confines of the ganglia of the above nerves, in company with the cell-bodies of their sensory neurones. This is thought to be especially true for the geniculate, the petrosal and the jugular ganglion. Therefore these ganglia must be considered as in small part sympathetic ganglia.
The gangliated cephalic plexus could properly be included as a division of the general sympathetic system described later. However, because its larger ganglia are so intimately associated with branches of the oculomotor, trigeminal, masticator, glosso-palatine, glosso-pharyngeal and vagus nerves, it is customary to describe it in connexion with the cranial nerves.
The larger ganglia, one on either side of the head, comprise the ciliary ganglion, the spheno-palatine (Meckel's) ganglion, the otic and the submaxillary ganglion. To these must be added portions of the geniculate, petrosal, jugular and the ganglion nodosum, and a part of the superior cervical sympathetic ganglion. The chief relations of the gangliated cephalic plexus to the cranial nerves are shown in the figure below.
The so-called roots and branches of the ganglia carry three varieties of fibers:
- Motor (visceral motor or preganglionic), and
Most roots and branches are mixed, the name of a root being determined only by the variety of fibers predominating in it.
A bundle of sensory fibers going to a ganglion is called its sensory root. Such, however, cannot comprise a true root since none of its fibers arises in the ganglion and very few or none may terminate in it. The only sensory fibers terminating in a ganglion are the few which may approach it in any of the roots to terminate in its capsule or the capsules of its cells and convey impulses of general sensibility from the ganglion to the central nervous system. Almost all of the fibers of a "sensory root" merely pass around or through a ganglion and into its branches beyond, which they borrow as paths for reaching their allotted fields of distribution. In this relation it should be realized that while the cihary, spheno-palatine, otic and submaxillary ganglia are customarily described under the discussion of the trigeminus, this nerve has functionally less to do with them than any of the other cranial nerves with which they are associated. Bundles of trigeminal (sensory) fibers, traceable in gross anatomy because meduUated and of appreciable size, pass to the gangha, but only to pass through them as continuations of the terminal branches of the trigeminus.
The so-called motor root of a ganglion may carry two kinds of fibers:
(a) visceral motor (preganglionic) fibers, arising in the nuclei of origin in the central system and passing in the trunk and branches of a cranial nerve (oculomotor, masticator, etc.) to enter and terminate in contact with the ceU-bodies of the ganglion, which, in their turn, give fibers to the branches of the ganglion;
(b) fibers of the same origin, name and course but which may pass thi-ough the ganglion to terminate in contact with the cells of a more distant ganglion. Any root, the motor especially, may contain somatic motor fibers, that is, fibers of central origin which pass through the ganglion uninterrupted and into its branches to terminate upon the fibers of skeletal (voluntary) muscle.
A sympathetic root likewise may carry two and perhaps three varieties of fibers conforming to the name:
(a) fibers arising from the cells of other sympathetic gangha and terminating in the ganglion in question;
(b) fibers arising in other ganglia which pass through the gangfion in question to enter its branches and terminate either in other ganglia or upon their allotted muscular or glandular elements. A third is the fiber of the sensory sympathetic neurone, probably quite rare, which may arise from a cell-body in the ganglion and pass centralward in its root and in the appropi'iate cranial nerve to terminate about a cell-body of the dorsal-root or spinal ganglion type, the central process of which latter conveys this sensory impulse of sympathetic origin into the central system just as sensory oranio-spinal impulses are conveyed.
Branches of distribution
The branches of distribution of the gangha, the larger of them often called nerves, are those bundles in which the fibers, both arising in or passing through the gangha, course toward their terminations upon their allotted tissue elements of the head. The larger gangha of the head are described as each possessing the three roots above mentioned. In the branches pass fibers motor to the vessels of the head, to the intrinsic muscles of the eye bulb, to the [lacrimal glands, the mucous membranes (gland cells) of the nasal and oral cavities and the salivary glands, and sensory fibers conveying impulses from these structures.
The plexuses into which the gangliated cephalic plexus is divided and which connect the ganglia to form it, are numerous and vary greatly in size. They underlie the mucous membranes and they surround all the vessels and glands. They are named according to their locahty. The largest of them are the tympanic plexus and the carotid and cavernous plexuses. They have been repeatedly referred to in their relations to the branches of the cranial nerves.
Of the numerous branches described from the superior cervical sympathetic ganglion, the two large ones which pass upward associate it especially with the gangliated cephalic plexus. That branch known as the internal carotid nerve may be considered as the direct continuation upward of the gangUated sympathetic trunk of the body. Through the branches of this, the carotico-tympanic and the deep petrosal nerves, and through the plexuses derived from it, the superior cervical ganglion may be associated with practically all the other sympathetic gangha of the head. The other branch from the superior cervical ganglion, the jugular nerve, associates it with the ganglia of the glosso-pharyngeal and vagus nerves, with the petrosa gangion by a direct branch and with the gangha of the vagus through the nodosal plexus. These latter gangha (and the nerves to which they belong) are connected, chiefly by way of the tympanic nerve, which is from the petrosal ganglion, with the tympanic plexus.
The tympanic plexus serves as a common point of distribution of fibers from the superior cervical sympathetic ganglion, the gangha of the vagus, the petrosal ganglion, and the geniculate ganglion, to the cavernous and carotid plexuses and to the spheno-palatine and otic ganglia. The superior cervical ganglion is associated with the cavernous and carotid plexuses direct by the internal carotid nerve and with the tympanic plexus by the Inferior and superior carotico-tympanic nerves. The tympanic plexus receives fibers from the geniculate ganglion by a small geniculo-tympanic branch and it is connected with the spheno-palatine ganglion by a small anastomotic or tympano-petrosal branch to the great superficial petrosal nerve, and with the otic ganglion by the small superficial petrosal nerve. It is not directly connected with either the cihary or the submaxillary ganglion. However, these ganglia, as well as the sphenopalatine and otic, are connected with the carotid plexus either directly by named branches or indirectly by way of plexuses derived from the carotid. The geniculo-tympanic branch, the tympanic nerve and twigs of the nodosal plexus may be considered as analogous to the rami oommunicantes of the spinal nerves.
The parotid branches, described above as branches of the auriculo-temporal nerve (from the trigeminus) and as containing fibers from the glossopharyngeal, should be mentioned here as belonging to the gangliated cephalic plexus. These branches are sympathetic fibers arising in the otic ganglion and passing as branches of the ganglion to the auriculo-temporal in which they remain till this nerve enters the parotid gland and then they are distributed to the gland. The visceral motor or preganglionic fibers which terminate about their cells of origin in the otic ganglion are derived from the glosso-pharyngeal nerve and pass successively through the tympanic nerve, the tympanic plexus, and the small superficial petrosal nerve to the otic ganglion.
The tympanic nerve (tympanic branch of the glosso-pharyngeal, or nerve of Jacobson), the branch to the Eustachian tube (ramus tubes), and the superior and inferior carotico-lympanic branches are also described as branches of the glosso-pharyngeal nerve. These must hkewise be considered as belonging to the gangliated cephahc plexus.
For purposes of dissection, it may be more expedient to consider separately, with its roots and branches, each of the larger ganglia of the gangliated cephalic plexus. Under this heading belong in part the geniculate ganglion of the glosso-palatine nerve, and the ganglia of the glosso-pharyngeal and vagus, especially the petrosal ganglion of the former and the jugular ganglion of the latter, from the fact that these ganglia contain numerous cell-bodies of sympathetic neurones as well as those of the sensory neurones of their nerves.
These ganglia, however, have been described with their corresponding cranial nerves. The sensory and motor roots of their sympathetic portions are contained in the roots of their nerves. The geniculate probably has no sympathetic root. The sympathetic roots of the petrosal and jugular ganglia are contained in the branches of the jugular nerve. The chief branches of distribution of the geniculate are the geniculo-tympanic branch, the great superficial petrosal nerve, and the external superficial petrosal nerve. The branches of the petrosal ganglion are the tympanic nerve and its branches of the tympanic plexus. The chief branch of distribution from the jugular ganglion is contained in the auricular branch of the vagus, or nerve of Arnold, supplemented by sympathetic fibers in the trunk of the vagus itself.
The principal cephalic sympathetic ganglia are the ciliary, the spheno-palatine (Meckel's), the otic and the submaxillary.
The Ciliary Ganglion
The ciliary, lenticular, or ophthalmic ganglion lies in the posterior part of the orbital cavity, about 6 mm. in front of the superior orbital (sphenoidal) fissure, to the lateral side of the optic nerve, and between the optic nerve and the external rectus muscle. It is a small, reddish, quadrangular body, compressed laterally, and it measures about two millimetres from before backward.
- Its motor or short root enters its lower and posterior angle and is a visceral motor branch derived from the branch of the inferior division of the oculomotor nerve which supplies the inferior oblique muscle. The fibers of the motor root probably all terminate in the ciliary ganglion in connection with motor sympathetic neurones.
- The sensory or long root passes through the upper and back part of the ganglion. It is a branch of the naso-oiliary (nasal) nerve and is, therefore, composed of fibers from the trigeminus passing through the ganglion.
- The sympathetic root consists of fibers derived from the cavernous plexus of the sympathetic; it passes to the ganglion with the long root.
From three to six short ciliary nerves emerge from the anterior border of the ganglion ; they divide as they pass forward and eventually form about twenty nerves which are arranged in aii upper and a lower group, and the latter group is joined by the long ciliary branches of the naso-ciliary (nasal) nerve, now sensory and sympathetic. When they reach the eyeball, the ciliary nerves pierce the sclerotic around the optic nerve, and pass forward in grooves on the inner surface of the sclera. The sympathetic fibers contained are distributed as motor fibers to the ciliary muscle, the sphincter of the iris, and to the vessels of these and of the cornea.
The Spheno-palatine or Meckel's Ganglion
This ganglion is associated with the maxillary nerve. It is a small reddish-grey body of triangular form, which is flattened at the sides, and measiu-es about five millimetres from before backward. It lies deeply in the pterygo-palatine (spheno-maxillary) fossa at the lateral side of the spheno-palatine foramen and in front of the anterior end of the pterygoid (Vidian) canal. It is attached to the maxillary nerve, from which it receives its sensory root, and it is connected with the Vidian nerve, which furnishes it with motor and sympathetic filaments.
The exact position of the ganglion depends upon the size and shape of the sphenoidal air cells. When these are small, or high and narrow, the ganglion lies lateral to them; when they are large, or broad and fiat, the ganglion lies inferior to them. Sometimes it may lie anterior to them if the cells are short from in front backward. The ganglion may be reached with ease by chipping away the bone around the sphenoidal air cells after the skull is divided sagitally.
(a) Its motor root, consisting of visceral motor fibers of the glosso-palatine nerve, is contained in the great superficial petrosal nerve which is incorporated in the Vidian nerve. It springs from the anterior angle of the geniculate ganglion and passes through the hiatus of the facial canal (hiatus Fallopii) into the middle fossa of the cranium, where it runs forward and medialward, in a groove on the upper surface of the petrous part of the temporal bone, to the foramen laoerum, and in this part of its course it passes beneath the semilunar (Gasserian) ganglion and the masticator nerve. In the foramen lacerum it joins with the great deep petrosal nerve to form the Vidian nerve (nerve of the pterygoid canal), which passes forward through the pterygoid (Vidian) canal and its motor and sympathetic fibers terminate in the spheno-palatine ganglion in the pterygo-palatine (spheno-maxillary) fossa. The great superficial petrosal nerve contains sensory as well as sympathetic and motor fibers. The sensory fibers pass through the ganglion and, in the small palatine nerve, descend to the soft palate, where they terminate in the epithelium covering it and some are probably concerned with peripheral taste organs found there. They arise from the cells of the geniculate ganglion and therefore belong to the glosso-palatine nerve.
(b) The sympathetic root is the great deep petrosal portion of the Vidian nerve. This root, which is of reddish colour and of soft texture, springs from the carotid plexus which lies on the outer side of the internal carotid artery in the carotid canal. It enters the foramen lacerum through the apex of the petrous portion of the temporal bone, and unites with the great superficial petrosal branch of the facial nerve to form the Vidian nerve. The great superficial petrosal nerve also carries sympathetic fibers to the spheno-palatine ganglion, derived from the geniculate ganglion and from the tj'mpanic plexus.
The Vidian nerve [n. canalis pterygoidei] commences by the union of the great superficial and deep petrosal nerves in the foramen lacerum, and runs forward through the pterygoid (Vidian) canal to the pterygo-palatine (spheno-maxillary) fossa to the spheno-palatine ganglion. The Vidian nerve often may be seen in a ridge of bone along the floor of the sphenoidal cells and its direction there depends upon the position of the spheno-palatine ganglion. While it is in the pterygoid canal the Vidian nerve is joined by a sphenoidal filament from the otic ganglion, and it gives branches to the upper and back part of the roof and septum of the nose, and to the lower end of the Eustachian tube.
(c) The sensory roots consist of the sensory fibers mentioned above in the great superficial petrosal nerve and of usually two spheno-palatine branches from the maxillary nerve. The majority of the fibers of these roots do not join the ganglion, but pass by its medial side and enter the palatine branches.
The branches of the ganglion, containing sensory, vaso-motor and secretory fibers, are orbital or ascending, internal or nasal, descending or palatine, and posterior or pharyngeal.
The orbital or ascending branches are two or three small twigs which enter the orbit through the inferior orbital (spheno-maxillary) fissure and proceed, within the periosteum, to the inner wall of the orbit, where they pass through the posterior ethmoidal foramen and through the foramina in the suture behind that foramen to be distributed to the mucous membrane which lines the posterior ethmoidal cells and the sphenoidal sinus.
The internal or nasal branches are derived in part from the medial side of the ganglion, but are also largely made up of fibers which pass from the spheno-palatine branches of the maxillary nerve without traversing the ganglionic substance. They are disposed in two sets, the lateral and the medial (septal) posterior superior nasal branches.
The lateral posterior superior nasal branches are six or seven small twigs which pass through the spheno-palatine foramen, and are distributed to the mucous membrane covering the posterior parts of the superior and middle nasal conchae (turbinated bones). They also furnish twigs to the lining membrane of the posterior etlimoidal cells.
The medial posterior superior nasal (septal) branches, two or three in number, pass medial-ward through the spheno-palatine foramen. They cross the roof of the nasal fossa to reach the back part of the nasal septum, where the smaller twigs terminate. The largest nerve of the set, the naso-palatine nerve, or nerve of Cotunnius, runs downward and forward in a groove in the vomer between the periosteum and the mucous membrane to the incisive (anterior palatine) canal, where it communicates with the nasal branch of the anterior superior alveolar nerve. The two naso-palatine nerves then pass through the foramina of Scarpa in the intermaxillary suture, the left nerve passing through the anterior of the two foramina. In the lower part of the incisive (anterior palatine) canal the two nerves form a plexiform communication (formerly described as Cloquet's ganglion) and they furnisli twigs to the anterior or premaxillary part of the hard palate behind the incisor teeth. In this situation they communicate with the anterior palatine nerves.
The descending branches are the great or anterior, the posterior, and the middle (external) palatine nerves. Like the internal set of branches, they are in part derived from the ganglion and in part are directly continuous with the spheno-palatine nerves.
The great or anterior palatine nerve, its sensory fibers derived from the maxillary nerve, arises from the inferior angle of Meckel's ganglion, and passes downward through the pterygo-palatine canal, accompanied by the descending palatine artery. Emerging from the canal at the greater (posterior) palatine foramen it divides into two or three branches, which pass forward in gi-ooves in the hard palate and supply the glands and mucous membrane of the hard palate and the gums on the inner aspect of the alveolar border of the upper jaw. During its cour.se through the pterygo-palatine canal the anterior palatine nerve gives off the posterior inferior nasal nerves. These nerves pass through small openings in the perpendicular plate of the palate bone to supply the mucous membrane covering the posterior part of the inferior nasal concha (turbinated bone) and the adjacent portions of the middle and inferior meatuses of the nose.
The posterior or small palatine nerve passes downward through a lesser palatine foramen (accessory palatine canal), and enters the soft palate, distributing branches to that organ, to the uvula, and to the tonsil. Its sensory fibers are derived from the glosso-palatine nerve, through the great superficial petrosal nerve and through the spheno-palatine ganglion. It was formerly believed to convey motor fibers from the facial nerve to the levator palati and azygos uvulae, but it is now beheved that these muscles are supplied by the spinal accessory nerve through the pharyngeal plexus.
The middle (external) palatine nerve, the smallest of the three, in part, likewise from the glosso-palatine nerve, traverses a lesser palatine foramen and supplies twigs to the tonsil and to the adjacent part of the soft palate.
The pharyngeal branch, which is of small size, passes backward and somewhat medialward through the pharyngeal canal accompanied by a pharyngeal branch of the spheno-palatine artery. It is distributed to the mucous membrane of the uppermost part of the pharynx, to the upper part of the posterior nares, to the opening of the Eustachian tube, and to the lining of the sphenoidal sinus. Its sensory fibers are derived from the maxillary nerve.
The Otic Ganglion
The otic or Arnold's ganglion is a small reddish-grey body which is associated with the mandibular nerve. It lies deeply in the zygomatic fossa, immediately below the foramen ovale, on the inner side of the trunk of the mandibular nerve. It is in relation internally with the tensor palati, which separates it from the Eustachian tube. In front of it is the posterior border of the pterygoideus internus, and behind it lie the middle and small meningeal arteries. It is compressed laterally, and its greatest diameter, which lies antero-posteriorly, is about three millimetres.
The ganglion is closely connected with the nerve to the pterygoideus internus, through which it may receive a motor root from the masticator nerve. Through the small superficial petrosal nerve, which joins the upper and back part of the ganglion, it receives a motor root from the glosso-palatine nerve and sensory and motor fibers from the glosso-pharyngeal nerve. It receives also a slender sphenoidal filament from the Vidian nerve. The sympathetic roots are derived from the small superficial petrosal nerve and from the sympathetic plexus on the middle meningeal artery.
The communicating branches which pass from the ganglion are:
- The filaments to the chorda tympani; some of whose fibers probably terminate in the submaxillary ganglion;
- filaments to the auriculo-temporal nerve;
- filaments to the spinous nerve (the recurrent branch of the mandibular nerve). The branches of distribution are sympathetic to the vessels and somatic motor branches to the tensor tympani, and tensor veli palatini.
The Submaxillary Ganglion
The submaxillary ganglion is suspended from the lingual division of the mandibular nerve by anterior and posterior branches. It is a small reddish body, of triangular or fusiform shape, which lies between the mylo-hyoideus and hyoglossus and above the duct of the submaxillary gland.
The sensory root is received from the lingual nerve. The motor root is from both the masticator nerve by way of the lingual nerve, and from the glosso-palatine nerve by way of the chorda tympani. The motor fibers pass from the chorda tympani after it has joined the lingual, and the sensory fibers come directly from the lingual nerve. The sympathetic root is formed by filaments from the sympathetic plexus on the facial artery.
- Five or six glandular branches are given to the submaxillary gland and to Wharton's duct.
- Branches to the lingual nerve and the sublingual gland.
- To the mucous membrane of the floor of the mouth.