1.     1st division of trigeminal nerve 

2.     2nd division of trigeminal nerve

3.     3rd division of trigeminal nerve

Lesson No 21

Theme 1.  I division of V cranial nerve, areas of distribution. Ciliary ganglion

V Trigeminal nerve has one motor nucleus and mesencephalic, pontine & spinal sensory nuclei. They localised in pons (rhomboid fossa), mesencephalon and spinal cord. Nerve starts from brain by sensory rootlet and motor rootlet between pons and middle cerebellar pedunculi. Sensory rootlet represents by central process of sensory cells, which lie in trigeminal ganglion (Gasser`s) on top of pyramide of temporal bone. This ganglion is contained in trigeminal cavity (Меckel`s) which is formed by dura mater. Motor rootlet represents by axons from motor cells (motor nucleus).

Trigeminal nerve passes from skull by three divisions:

1.     Ophthalmic nerve, sensory, exits  from skull through the superior orbital fissura;

2.     Maxillary nerve, sensory, exits  from skull through the rotundum foramen;

3.     Mandibular nerve, mixed, exits from skull through the ovale foramen.

1.1          Ophthalmic nerve fossa subdivides in orbital into frontal nerve, lacrimal nerve and nasociliary nerve. Nasociliary nerve passes on superomedial wall of orbite and under block innervating medial eye corner and nose. Sensory long ciliary nerves pass to the coats of the eyeball, short ciliary nerves pass through the ciliary ganglion and carry parasympathetic and sympathetic fibres for eyeball with all its  tissues and muscles (sphincter pupillae, dilator pupillae and ciliary muscle). Posterior and anterior ethmoidal nerves pass through the posterior and anterior ethmoidal foramen. They innervate mucous membrane of ethmoidal cells (air sinus) and anterior part of nose cavity.

 

Frontal nerve passes on middle part of upper wall of orbite and passes on forehead skin over supraorbital and frontal notches by three branches, innervating forehead skin and top eyelid. Lacrimal nerve passes on upper-lateral wall of orbite, transfixes a lacrimal gland, innervating it. Passing out from gland, it innervates the skin of lateral eye corner. Postganglionic and parasympathetic fibres from pterygopalatine ganglion (which pass with zygomatic nerve) pass to lacrimal nerve and provide a secretory innervation of the lacrimal gland.

Fifth Or The trigeminal nerve is the largest cranial nerve and is the great sensory nerve of the head and face, and the motor nerve of the muscles of mastication.

  It emerges from the side of the pons, near its upper border, by a small motor and a large sensory root—the former being situated in front of and medial to the latter.

 

 

Motor Root.—The fibers of the motor root arise from two nuclei, a superior and an inferior. The superior nucleus consists of a strand of cells occupying the whole length of the lateral portion of the gray substance of the cerebral aqueduct. The inferior or chief nucleus is situated in the upper part of the pons, close to its dorsal surface, and along the line of the lateral margin of the rhomboid fossa. The fibers from the superior nucleus constitute the mesencephalic root: they descend through the mid-brain, and, entering the pons, join with the fibers from the lower nucleus, and the motor root, thus formed, passes forward through the pons to its point of emergence. It is uncertain whether the mesencephalic root is motor or sensory.

 

Sensory Root.—The fibers of the sensory root arise from the cells of the semilunar ganglion which lies in a cavity of the dura mater near the apex of the petrous part of the temporal bone. They pass backward below the superior petrosal sinus and tentorium cerebelli, and, entering the pons, divide into upper and lower roots. The upper root ends partly in a nucleus which is situated in the pons lateral to the lower motor nucleus, and partly in the locus cæruleus; the lower root descends through the pons and medulla oblongata, and ends in the upper part of the substantia gelatinosa of Rolando. This lower root is sometimes named the spinal root of the nerve. Medullation of the fibers of the sensory root begins about the fifth month of fetal life, but the whole of its fibers are not medullated until the third month after birth.

  The Semilunar Ganglion (ganglion semilunare [Gasseri]; Gasserian ganglion) occupies a cavity (cavum Meckelii) in the dura mater covering the trigeminal impression near the apex of the petrous part of the temporal bone. It is somewhat crescentic in shape, with its convexity directed forward: medially, it is in relation with the internal carotid artery and the posterior part of the cavernous sinus. The motor root runs in front of and medial to the sensory root, and passes beneath the ganglion; it leaves the skull through the foramen ovale, and, immediately below this foramen, joins the mandibular nerve. The greater superficial petrosal nerve lies also underneath the ganglion.

  The ganglion receives, on its medial side, filaments from the carotid plexus of the sympathetic. It give off minute branches to the tentorium cerebelli, and to the dura mater in the middle fossa of the cranium. From its convex border, which is directed forward and lateralward, three large nerves proceed, viz., the ophthalmic, maxillary, and mandibular. The ophthalmic and maxillary consist exclusively of sensory fibers; the mandibular is joined outside the cranium by the motor root.

  Associated with the three divisions of the trigeminal nerve are four small ganglia. The ciliary ganglion is connected with the ophthalmic nerve; the sphenopalatine ganglion with the maxillary nerve; and the otic and submaxillary ganglia with the mandibular nerve. All four receive sensory filaments from the trigeminal, and motor and sympathetic filaments from various sources; these filaments are called the roots of the ganglia.

  The Ophthalmic Nerve (n. ophthalmicus) or first division of the trigeminal, is a sensory nerve. It supplies branches to the cornea, ciliary body, and iris; to the lacrimal gland and conjunctiva; to the part of the mucous membrane of the nasal cavity; and to the skin of the eyelids, eyebrow, forehead, and nose. It is the smallest of the three divisions of the trigeminal, and arises from the upper part of the semilunar ganglion as a short, flattened band, about 2.5 cm. long, which passes forward along the lateral wall of the cavernous sinus, below the oculomotor and trochlear nerves; just before entering the orbit, through the superior orbital fissure, it divides into three branches, lacrimal, frontal, and nasociliary.

Nerves of the orbit. Seen from above.

 

The ophthalmic nerve is joined by filaments from the cavernous plexus of the sympathetic, and communicates with the oculomotor, trochlear, and abducent nerves; it gives off a recurrent filament which passes between the layers of the tentorium.

Nerves of the orbit, and the ciliary ganglion. Side view.

 

  The Lacrimal Nerve (n. lacrimalis) is the smallest of the three branches of the ophthalmic. It sometimes receives a filament from the trochlear nerve, but this is possibly derived from the branch which goes from the ophthalmic to the trochlear nerve. It passes forward in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior orbital fissure. In the orbit it runs along the upper border of the Rectus lateralis, with the lacrimal artery, and communicates with the zygomatic branch of the maxillary nerve. It enters the lacrimal gland and gives off several filaments, which supply the gland and the conjunctiva. Finally it pierces the orbital septum, and ends in the skin of the upper eyelid, joining with filaments of the facial nerve. The lacrimal nerve is occasionally absent, and its place is then taken by the zygomaticotemporal branch of the maxillary. Sometimes the latter branch is absent, and a continuation of the lacrimal is substituted for it.

  The Frontal Nerve (n. frontalis) is the largest branch of the ophthalmic, and may be regarded, both from its size and direction, as the continuation of the nerve. It enters the orbit through the superior orbital fissure, and runs forward between the Levator palpebræ superioris and the periosteum. Midway between the apex and base of the orbit it divides into two branches, supratrochlear and supraorbital.

  The supratrochlear nerve (n. supratrochlearis), the smaller of the two, passes above the pulley of the Obliquus superior, and gives off a descending filament, to join the infratrochlear branch of the nasociliary nerve. It then escapes from the orbit between the pulley of the Obliquus superior and the supraorbital foramen, curves up on to the forehead close to the bone, ascends beneath the Corrugator and Frontalis, and dividing into branches which pierce these muscles, it supplies the skin of the lower part of the forehead close to the middle line and sends filaments to the conjunctiva and skin of the upper eyelid.

  The supraorbital nerve (n. supraorbitalis) passes through the supraorbital foramen, and gives off, in this situation, palpebral filaments to the upper eyelid. It then ascends upon the forehead, and ends in two branches, a medial and a lateral, which supply the integument of the scalp, reaching nearly as far back as the lambdoidal suture; they are at first situated beneath the Frontalis, the medial branch perforating the muscle, the lateral branch the galea aponeurotica. Both branches supply small twigs to the pericranium.

  The Nasociliary Nerve (n. nasociliaris; nasal nerve) is intermediate in size between the frontal and lacrimal, and is more deeply placed. It enters the orbit between the two heads of the Rectus lateralis, and between the superior and inferior rami of the oculomotor nerve. It passes across the optic nerve and runs obliquely beneath the Rectus superior and Obliquus superior, to the medial wall of the orbital cavity. Here it passes through the anterior ethmoidal foramen, and, entering the cavity of the cranium, traverses a shallow groove on the lateral margin of the front part of the cribriform plate of the ethmoid bone, and runs down, through a slit at the side of the crista galli, into the nasal cavity. It supplies internal nasal branches to the mucous membrane of the front part of the septum and lateral wall of the nasal cavity. Finally, it emerges, as the external nasal branch, between the lower border of the nasal bone and the lateral nasal cartilage, and, passing down beneath the Nasalis muscle, supplies the skin of the ala and apex of the nose.

  The nasociliary nerve gives off the following branches, viz.: the long root of the ciliary ganglion, the long ciliary, and the ethmoidal nerves.

  The long root of the ciliary ganglion (radix longa ganglii ciliaris) usually arises from the nasociliary between the two heads of the Rectus lateralis. It passes forward on the lateral side of the optic nerve, and enters the postero-superior angle of the ciliary ganglion; it is sometimes joined by a filament from the cavernous plexus of the sympathetic, or from the superior ramus of the trochlear nerve.

  The long ciliary nerves (nn. ciliares longi), two or three in number, are given off from the nasociliary, as it crosses the optic nerve. They accompany the short ciliary nerves from the ciliary ganglion, pierce the posterior part of the sclera, and running forward between it and the choroid, are distributed to the iris and cornea. The long ciliary nerves are supposed to contain sympathetic fibers from the superior cervical ganglion to the Dilator pupillæ muscle.

  The infratrochlear nerve (n. infratrochlearis) is given off from the nasociliary just before it enters the anterior ethmoidal foramen. It runs forward along the upper border of the Rectus medialis, and is joined, near the pulley of the Obliquus superior, by a filament from the supratrochlear nerve. It then passes to the medial angle of the eye, and supplies the skin of the eyelids and side of the nose, the conjunctiva, lacrimal sac, and caruncula lacrimalis.

  The ethmoidal branches (nn. ethmoidales) supply the ethmoidal cells; the posterior branch leaves the orbital cavity through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus.

 

The Ciliary Ganglion (ophthalmic or lenticular ganglion) is a small, sympathetic ganglion, of a reddish-gray color, and about the size of a pin’s head; it is situated at the back part of the orbit, in some loose fat between the optic nerve and the Rectus lateralis muscle, lying generally on the lateral side of the ophthalmic artery.

Plan of oculomotor nerve.

 

  Its roots are three in number, and enter its posterior border. One, the long or sensory root, is derived from the nasociliary nerve, and joins its postero-superior angle. The second, the short or motor root, is a thick nerve (occasionally divided into two parts) derived from the branch of the oculomotor nerve to the Obliquus inferior, and connected with the postero-inferior angle of the ganglion. The motor root is supposed to contain sympathetic efferent fibers (preganglionic fibers) from the nucleus of the third nerve in the mid-brain to the ciliary ganglion where they form synapses with neurons whose fibers (postganglionic) pass to the Ciliary muscle and to Sphincter muscle of the pupil. The third, the sympathetic root, is a slender filament from the cavernous plexus of the sympathetic; it is frequently blended with the long root. According to Tiedemann, the ciliary ganglion receives a twig of communication from the sphenopalatine ganglion.

  Its branches are the short ciliary nerves. These are delicate filaments, from six to ten in number, which arise from the forepart of the ganglion in two bundles connected with its superior and inferior angles; the lower bundle is the larger. They run forward with the ciliary arteries in a wavy course, one set above and the other below the optic nerve, and are accompanied by the long ciliary nerves from the nasociliary. They pierce the sclera at the back part of the bulb of the eye, pass forward in delicate grooves on the inner surface of the sclera, and are distributed to the Ciliaris muscle, iris, and cornea. Tiedemann has described a small branch as penetrating the optic nerve with the arteria centralis retinæ.

Central part of parasympathetic division consists of the cranial part and pelvic part. Cranial part located in midbrain and rhomboid fossa. Mesencephalic portion contains accessory oculomotor (Yakubovych-Edinger-Westphal) nucleus, and bulbar portion contains superior salivary nucleus and inferior salivary nucleus and dorsal nucleus of vagus nerve. Pelvic part carries the parasympathetic nuclei, which lie in gray matter of sacral segments S_II - S_IV of spinal cord.

Peripheral part consists of the ganglia, nerves and fibers.

Ciliary ganglion is formed by bodies of second /postganglionic/ neurons. It positioned in orbite near the optic nerve. The preganglionic fibres start from accessory oculomotor (Yakubovych-Edinger-Westphal) nucleus in composition of oculomotor nerve and separate from inferior branch as a radix oculomotorius, terminate by synapse with cells in ciliary ganglion. The postganglionic nervous fibres in composition of short ciliary nerves (nervi ciliares breves) pass to sphincter muscle of pupil and ciliary muscle. Sensory branches of nasociliary nerve and sympathetic postganglionic fibres from cavernous plexus pass through the ganglion.

 

Theme 2. 2nd divisions of trigeminal nerve.

areas of distribution. Autonomic nerves of the head

Maxillary nerve passes through the rotundum foramen and reaches the pterygopalatine fossa, where ramifies on three branches: infraorbital nerve, zygomatic nerve and ganglionic branches to pterygopalatine ganglion.

 Infraorbital nerve passes through the inferior orbital fissura enters into orbite, where lies on its lower wall, passes in infraorbital fissura and infraorbital sulcus and canal. Nerve passes into canine fossa, forming ‘pes anserinus minor’. There are inferior palpebral, external nasal and superior labial nerves that innervate skin from medial eye corner to mouth corner. Superior alveolar nerves (posterior, middle and inferior) start from infraorbital nerve in maxilla. They innervate mucous membrane of the maxillary (Haymori) sinus and form superior dental plexus. The last gives off the superior dental nerves and superior gingival branches of the upper jaw.

Distribution of the maxillary and mandibular nerves, and the submandibular ganglion.

 

Zygomatic nerve passes through the inferior orbital fissura entering orbite. Then it passes into zygomaticoorbital foramen and divided into zygomaticofacial and zygomaticotemporal sensory branches for skin of face and temporal region. Zygomatic nerve carries postganglionic parasympathetic fibres from pterygopalatine ganglion and gives off them to lacrimal nerve. Parasympathetic fibres provide secretory innervation of the lacrimal gland.

The ganglionic branches start from maxillary nerve and pass to pterygopalatine ganglion. Postganglionic branches include greater palatine nerve and lesser palatine nerve that pass through the greater palatine canal and lesser palatine foramens, innervating mucous membrane of the hard and soft palatine. The posterior nasal (medial and lateral) nerves pass through the sphenopalatine foramen pass into nasal cavity, where innervate mucous membrane of the nasal cavity. Nasopalatine nerve (Scarp’) start from the nasal branches and reach the mucous membrane of the hard palatine through the incisive canal. Postganglionic parasympathetic fibres from pterygopalatine ganglion are in composition of these nerves.

INNERVATION

The infratemporal fossa contains the major subdivisions of the mandibular branch of the trigeminal nerve, together with the chorda tympani, which enters the fossa and joins the lingual nerve, and the otic ganglion, which is functionally related to the parotid gland. The main sensory branches of the mandibular nerve extend beyond the infratemporal fossa and their distribution to the face is described in Chapter 29.

Mandibular nerve

The mandibular nerve is the largest trigeminal division and is a mixed nerve. Its sensory branches supply the teeth and gums of the mandible, the skin in the temporal region, part of the auricle – including the external meatus and tympanic membrane – and the lower lip, the lower part of the face and the mucosa of the anterior two-thirds (presulcal part) of the tongue and the floor of the oral cavity (Figs 31.12, 31.13A, 31.15). The motor branches innervate the muscles of mastication. The large sensory root emerges from the lateral part of the trigeminal ganglion and exits the cranial cavity through the foramen ovale. The small motor root passes under the ganglion and through the foramen ovale to unite with the sensory root just outside the skull. As it descends from the foramen ovale, the nerve is usually around 4 cm from the surface and a little anterior to the neck of the mandible. The mandibular nerve immediately passes between tensor veli palatini, which is medial, and lateral pterygoid, which is lateral, and gives off a meningeal branch and the nerve to medial pterygoid from its medial side. The nerve then divides into a small anterior and large posterior trunk. The anterior division gives off branches to the four main muscles of mastication and a buccal branch which is sensory to the cheek. The posterior division gives off three main sensory branches, the auriculotemporal, lingual and inferior alveolar nerves, and motor fibres to supply mylohyoid and the anterior belly of digastric.

Fig. 31.15 Arteries and nerves of the head, deepest lateral regions. (From Sobotta 2006.)

Meningeal branch (nervus spinosus)

The meningeal branch re-enters the cranium through the foramen spinosum with the middle meningeal artery. It divides into anterior and posterior branches which accompany the main divisions of the middle meningeal artery and supply the dura mater in the middle cranial fossa and, to a lesser extent, in the anterior fossa and calvarium.

Nerve to medial pterygoid

The nerve to medial pterygoid is a slender ramus which enters the deep aspect of the muscle. It supplies one or two filaments that pass through the otic ganglion without interruption to supply tensor tympani and tensor veli palatini.

Anterior trunk of mandibular nerve

The anterior trunk of the mandibular nerve gives rise to the buccal nerve, which is sensory, and the masseteric, deep temporal and lateral pterygoid nerves, which are all motor.

Buccal nerve

The buccal nerve passes between the two heads of lateral pterygoid. It descends deep to the tendon of temporalis, passes laterally in front of masseter, and anastomoses with the buccal branches of the facial nerve. It carries the motor fibres to lateral pterygoid, and these are given off as the buccal nerve passes through the muscle. It may also give off the anterior deep temporal nerve. The buccal nerve supplies sensation to the skin over the anterior part of buccinator and the buccal mucous membrane, together with the posterior part of the buccal gingivae adjacent to the second and third molar teeth.

Nerve to masseter

The nerve to masseter passes laterally above lateral pterygoid, on to the skull base, anterior to the temporomandibular joint and posterior to the tendon of temporalis. It crosses the posterior part of the mandibular notch with the masseteric artery and ramifies on and enters the deep surface of masseter. It also provides articular branches which supply the temporomandibular joint.

Deep temporal nerves

The deep temporal nerves usually consist of two branches, anterior and posterior, although there may be a middle branch. They pass above lateral pterygoid to enter the deep surface of temporalis. The anterior nerve frequently arises as a branch of the buccal nerve. The small posterior nerve sometimes arises in common with the nerve to masseter.

Nerve to lateral pterygoid

The nerve to lateral pterygoid enters the deep surface of the muscle. It may arise separately from the anterior division of the mandibular nerve or from the buccal nerve.

Posterior trunk of mandibular nerve

The posterior trunk of the mandibular nerve is larger than the anterior and is mainly sensory, although it receives fibres from the motor root for the nerve to mylohyoid. It divides into auriculotemporal, lingual and inferior alveolar (dental) nerves.

Auriculotemporal nerve

The auriculotemporal nerve usually has two roots which encircle the middle meningeal artery. It runs back under lateral pterygoid on the surface of tensor veli palatini, passes between the sphenomandibular ligament and the neck of the mandible, and then runs laterally behind the temporomandibular joint related to the upper part of the parotid gland. Emerging from behind the joint, it ascends over the posterior root of the zygoma, posterior to the superficial temporal vessels, and divides into superficial temporal branches. It communicates with the facial nerve and otic ganglion. The rami to the facial nerve, usually two, pass anterolaterally behind the neck of the mandible to join the facial nerve at the posterior border of masseter. Filaments from the otic ganglion join the roots of the auriculotemporal nerve close to their origin. The sensory distribution of the auriculotemporal nerve on the face is described in Chapter 29.

Lingual nerve

The lingual nerve is sensory to the mucosa of the anterior two-thirds of the tongue, the floor of the mouth and the mandibular lingual gingivae. It arises from the posterior trunk of the mandibular nerve and at first runs beneath lateral pterygoid and superficial to tensor veli palatini, where it is joined by the chorda tympani branch of the facial nerve, and often by a branch of the inferior alveolar nerve. Emerging from under cover of lateral pterygoid, the lingual nerve then runs downwards and forwards on the surface of medial pterygoid, and is thus carried progressively closer to the medial surface of the mandibular ramus. It becomes intimately related to the bone a few millimetres below and behind the junction of the vertical ramus and horizontal body of the mandible. Here it lies anterior to, and slightly deeper than, the inferior alveolar (dental) nerve. It next passes below the mandibular attachment of the superior pharyngeal constrictor and pterygomandibular raphe, closely applied to the periosteum of the medial surface of the mandible, until it lies opposite the posterior root of the third molar tooth, where it is covered only by the gingival mucoperiosteum. At this point it usually lies 2–3 mm below the alveolar crest and 0.6 mm from the bone, however in 5% of cases it lies above the alveolar crest. It next passes medial to the mandibular origin of mylohyoid, and this carries it progressively away from the mandible, and separates it from the alveolar bone covering the mesial root of the third molar tooth. The rest of the nerve is described with the mouth and oral cavity in Chapter 30.

Inferior alveolar (dental) nerve

The inferior alveolar nerve descends behind lateral pterygoid. At the lower border of the muscle the nerve passes between the sphenomandibular ligament and the mandibular ramus and enters the mandibular canal via the mandibular foramen. Below lateral pterygoid it is accompanied by the inferior alveolar artery, a branch of the first part of the maxillary artery, which also enters the canal with associated veins. The subsequent course of the inferior alveolar nerve is described in Chapter 30.

Otic ganglion

This is a small, oval, flat reddish-grey ganglion situated just below the foramen ovale. It is a peripheral parasympathetic ganglion related topographically to the mandibular nerve, but connected functionally with the glossopharyngeal nerve. Near its junction with the trigeminal motor root, the mandibular nerve lies lateral to the ganglion; tensor veli palatini lies medially, separating the ganglion from the cartilaginous part of the pharyngotympanic tube, and the middle meningeal artery is posterior to the ganglion. The otic ganglion usually surrounds the origin of the nerve to medial pterygoid.

Like all parasympathetic ganglia, there are three roots, motor, sympathetic and sensory. Only the parasympathetic fibres relay in the ganglion. The motor, parasympathetic, root of the otic ganglion is the lesser petrosal nerve, conveying preganglionic fibres from the glossopharyngeal nerve which originate from neurones in the inferior salivatory nucleus. The lesser petrosal nerve runs intracranially in the middle cranial fossa on the anterior surface of the petrous bone before passing through the foramen ovale to join the otic ganglion. The nerve synapses in the otic ganglion, and postganglionic fibres pass by a communicating branch to the auriculotemporal nerve and so to the parotid gland. The sympathetic root is from a plexus on the middle meningeal artery. It contains postganglionic fibres from the superior cervical sympathetic ganglion which traverse the otic ganglion without relay and emerge with parasympathetic fibres in the connection with the auriculotemporal nerve to supply blood vessels in the parotid gland. The sensory fibres from the gland are derived from the auriculotemporal nerve. Clinical observations suggest that in humans the gland also receives secretomotor fibres through the chorda tympani.

Branches

A branch connects the otic ganglion to the chorda tympani nerve, while another ramus ascends to join the nerve of the pterygoid canal. These branches may form an additional pathway by which gustatory fibres from the anterior two-thirds of the tongue may reach the facial ganglion without traversing the middle ear, and they do not synapse in the otic ganglion. Motor branches to tensor veli palatini and tensor tympani, derived from the nerve to medial pterygoid, also pass through the ganglion without synapsing.

Chorda tympani

The chorda tympani nerve enters the infratemporal fossa region by passing through the medial end of the petrotympanic fissure behind the capsule of the temporomandibular joint. The nerve descends medial to the spine of the sphenoid bone – which it sometimes grooves – lying posterolateral to tensor veli palatini. It is crossed medially by the middle meningeal artery, the roots of the auriculotemporal nerve and by the inferior alveolar nerve (Fig. 31.15). The chorda tympani joins the posterior aspect of the lingual nerve at an acute angle. It carries taste fibres for the anterior two-thirds of the tongue and efferent preganglionic parasympathetic (secretomotor) fibres destined for the submandibular ganglion in the floor of the mouth.

 

Nuclei of the V-XII Cranial Nerves

 

INTERNAL STRUCTURE

Transverse section of the medulla at the level of the pyramidal decussation

A transverse section across the lower medulla oblongata (Fig. 19.4) intersects the dorsal, lateral and ventral funiculi, which are continuous with their counterparts in the spinal cord. The ventral funiculi are separated from the central grey matter by corticospinal fibres, which cross in the pyramidal decussation to reach the contralateral lateral funiculi (see Fig. 19.8). The decussation displaces the central grey matter and central canal dorsally. Continuity between the ventral grey column and central grey matter, which is maintained throughout the spinal cord, is lost. The column subdivides into the supraspinal nucleus (continuous above with that of the hypoglossal nerve), which is the efferent source of the first cervical nerve, and the spinal nucleus of the accessory nerve, which provides some spinal accessory fibres and merges rostrally with the nucleus ambiguus.

Fig. 19.8 The decussation of the pyramids.

The dorsal grey column is also modified at this level as the nucleus gracilis appears as a grey lamina in the ventral part of the fasciculus gracilis. The nucleus begins caudal to the nucleus cuneatus, which invades the fasciculus cuneatus from its ventral aspect in similar fashion.

The spinal nucleus and spinal tract of the trigeminal nerve are visible ventrolateral to the dorsal columns. They are continuous with the substantia gelatinosa and tract of Lissauer of the spinal cord.

Transverse section of the medulla at the level of the decussation of the medial lemniscus

The medullary white matter is rearranged above the level of the pyramidal decussation (Fig. 19.5). The pyramids form two large ventral bundles flanking the ventral median fissure on the ventral surface of the medulla.

They contain corticospinal fibres of ipsilateral origin. The nucleus gracilis is prominent on the dorsal aspect, with diminishing numbers of fibres of the fasciculus gracilis located on its dorsal, medial and lateral margins. The nucleus cuneatus is well developed. Both nuclei retain continuity with the central grey matter at this level, but this is lost more rostrally. First-order afferent fibres contained within the fasciculi gracilis and cuneatus synapse upon neurones in their respective nuclei. Second-order axons emerge from the nuclei as internal arcuate fibres, at first curving ventrolaterally around the central grey matter and then ventromedially between the spinal tract of the trigeminal nerve and the central grey matter. The fibres decussate in the midline thereafter forming the medial lemniscus which ascends to the thalamus. The decussation of internal arcuate fibres is located dorsal to the pyramids and ventral to the central grey matter, which is therefore more dorsally displaced than in the previous section.

The medial lemniscus ascends from the decussation as a flattened tract, near the median raphe. The pyramidal tract lies ventrally, and the medial longitudinal fasciculus and the tectospinal tract lie dorsally. Decussating lemniscal fibres are rearranged as they cross, so that those derived from the nucleus gracilis come to lie ventral to those from the nucleus cuneatus. Above this level, the medial lemniscus is further rearranged so that ventral (gracile) fibres migrate laterally, whilst dorsal (cuneate) fibres migrate medially. After such rearrangement, the medial lemniscus is somatotopically organized with C1 to S4 spinal segments represented sequentially from medial to lateral.

The nucleus of the spinal tract of the trigeminal nerve is separated from the central grey matter by internal arcuate fibres, and from the lateral medullary surface by the spinal tract of the trigeminal and by some dorsal spinocerebellar tract fibres. The latter progressively incline dorsally, and enter the inferior cerebellar peduncle at a higher level.

Transverse section of the medulla at the caudal end of the fourth ventricle

A transverse section at the lower end of the fourth ventricle (Fig. 19.6) shows some new features together with most of those already described. The total area of grey matter is increased by the presence of the large olivary nuclear complex and nuclei of the vestibulocochlear, glossopharyngeal, vagus and accessory nerves.

Fig. 19.6 Transverse section through the medulla oblongata at the caudal end of the fourth ventricle.

A smooth, oval elevation, the olive, lies between the ventrolateral and dorsolateral sulci of the medulla. It is formed by the underlying inferior olivary complex of nuclei, and lies lateral to the pyramid, separated from it by the ventrolateral sulcus and emerging hypoglossal nerve fibres. The roots of the facial nerve emerge between its rostral end and the lower pontine border, in the cerebellopontine angle. The arcuate nuclei are curved, interrupted bands, ventral to the pyramids, and are said to be displaced pontine nuclei. Anterior external arcuate fibres and those of the striae medullares are derived from them. They project mainly to the contralateral cerebellum through the inferior cerebellar peduncle (Fig. 19.7).

Fig. 19.7 Some of the afferent components of the inferior cerebellar peduncles. The efferent components have been omitted.

The inferior olivary nucleus is an irregularly crenated mass of grey matter with a medially directed hilum, through which numerous fibres enter and leave the nucleus. It has prominent connections with the cerebellum and is described more fully in Chapter 20.

The central grey matter at this level constitutes the ventricular floor. It contains (sequentially from medial to lateral): the hypoglossal nucleus, dorsal motor nucleus of the vagus, nucleus solitarius, and the caudal ends of the inferior and medial vestibular nuclei.

The tractus solitarius and the associated nucleus solitarius extend throughout the length of the medulla. The tract is composed of general visceral afferents from the vagus and glossopharyngeal nerves. The nucleus and its central connections with the reticular formation subserve the reflex control of cardiovascular, respiratory and cardiac functions. The rostral portion of the tract consists of gustatory fibres from the facial, glossopharyngeal and vagal nerves; they project to the rostral pole of the nucleus solitarius, which is sometimes referred to as the gustatory nucleus.

The medial longitudinal fasciculus is a small compact tract near the midline, ventral to the hypoglossal nucleus, that is continuous with the ventral vestibulospinal tract. At this medullary level it is displaced dorsally by the pyramidal and lemniscal decussations. It ascends in the pons and midbrain, maintaining its relationship to the central grey matter and midline, and is therefore near the somatic efferent nuclear column. Fibres from a variety of sources course for short distances in the tract.

The spinocerebellar, spinotectal, vestibulospinal, rubrospinal and lateral spinothalamic (spinal lemniscal) tracts all lie in the ventrolateral area of the medulla at this level. The tracts are limited dorsally by the nucleus of the spinal tract of the trigeminal and ventrally by the pyramid.

Numerous islets of grey matter are scattered centrally in the ventrolateral medulla, an area intersected by nerve fibres that run in all directions. This is the reticular formation, which exists throughout the medulla and extends into the pontine tegmentum and midbrain.

Pyramidal tract

Each pyramid contains descending corticospinal fibres, derived from the ipsilateral cerebral cortex, which have traversed the internal capsule, midbrain and pons (Fig. 19.8). Approximately 70–90% of the axons leave the pyramids in successive bundles, crossing in and deep to the ventral median fissure as the pyramidal decussation. In the rostral medulla fibres cross by inclining ventromedially, whereas more caudally they pass dorsally, decussating ventral to the central grey matter. The decussation is orderly, such that fibres destined to end in the cervical segments cross first. Fibres continue to pass dorsally as they descend, and reach the contralateral spinal lateral funiculus as the crossed lateral corticospinal tract. Most uncrossed corticospinal fibres descend ventromedially in the ipsilateral ventral funiculus, as the ventral corticospinal tract. A minority run dorsolaterally to join the lateral corticospinal tracts as a small uncrossed component. The corticospinal tracts display somatotopy at almost all levels. In the pyramids the arrangement is like that at higher levels, in that the most lateral fibres subserve the most medial arm and neck movements. Similar somatotopy is ascribed to the lateral corticospinal tracts within the spinal cord.

Dorsal column nuclei

The nuclei gracilis and cuneatus are part of the pathway that is the major route for discriminative aspects of tactile and proprioceptive sensation. The upper regions of both nuclei are reticular and contain small and large multipolar neurones with long dendrites. The lower regions contain clusters of large round neurones with short and profusely branching dendrites. Upper and lower zones differ in their connections but both receive terminals from the dorsal spinal roots at all levels. Dorsal funicular fibres from neurones in the spinal grey matter terminate only in the superior, reticular zone. Variable ordering and overlap of terminals, on the basis of spinal root levels, occur in both zones. The lower extremity is represented medially, the trunk ventrally, and the digits dorsally. There is modal specificity, i.e. lower levels respond to low-threshold cutaneous stimuli, and upper reticular levels to inputs from fibres serving receptors in the skin, joints and muscles. The cuneate nucleus is divided into several parts. Its middle zone contains a large pars rotunda, in which rostrocaudally elongated medium-sized neurones are clustered between bundles of densely myelinated fibres. The reticular poles of its rostral and caudal zones contain scattered, but evenly distributed, neurones of various sizes. The pars triangularis is smaller and laterally placed.

There is a somatotopic pattern of termination of cutaneous inputs from the upper limb upon the cell clusters of the pars rotunda. Terminations are diffuse in the reticular poles.

The gracile and cuneate nuclei serve as relays between the spinal cord and higher levels. Primary spinal afferents synapse with multipolar neurones in the nuclei that form the major nuclear efferent projection. The nuclei also contain interneurones, many of which are inhibitory. Descending afferents from the somatosensory cortex reach the nuclei through the corticobulbar tracts, and appear to be restricted to the upper, reticular zones. These afferents both inhibit and enhance activity and are believed to be involved in sensory modulation. The reticular zones also receive connections from the reticular formation.

Neurones of dorsal column nuclei receive terminals of long, uncrossed, primary afferent fibres of the fasciculi gracilis and cuneatus, which carry information concerning deformation of skin, movement of hairs, joint movement and vibration. Unit recording of the neurones in dorsal column nuclei shows that their tactile receptive fields (i.e. the skin area in which a response can be elicited) vary in size, although they are mostly small, and are smallest for the digits. Some fields have excitatory centres and inhibitory surrounds, which means that stimulation just outside its excitatory field inhibits the neurone. Neurones in the nuclei are spatially organized into a somatotopic map of the periphery (in accord with the similar localization in the dorsal columns). In general, specificity is high. Many cells receive input from one or a few specific receptor types, e.g. hair, type I and II slowly adapting receptors and Pacinian corpuscles, and some cells respond to Ia muscle spindle input. However, some neurones receive convergent input from tactile pressure and hair follicle receptors.

A variety of control mechanisms can modulate the transmission of impulses through the dorsal column–medial lemniscus pathway. Concomitant activity in adjacent dorsal column fibres may result in presynaptic inhibition by depolarization of the presynaptic terminals of one of them. Stimulation of the sensory–motor cortex also modulates the transmission of impulses by both pre- and postsynaptic inhibitory mechanisms, and sometimes by facilitation. These descending influences are mediated by the corticospinal tract. Modulation of transmission by inhibition also results from stimulation of the reticular formation, raphe nuclei and other sites.

The accessory cuneate nucleus, dorsolateral to the cuneate nucleus, is part of the spinocerebellar system of precerebellar nuclei (Fig. 19.7). It contains large neurones like those in the spinal thoracic nucleus and receives the lateral fibres of the fasciculus cuneatus, which carry proprioceptive impulses from the upper limb that enter the cervical spinal cord rostral to the thoracic nucleus. The accessory cuneate neurones give rise to the posterior external arcuate fibres that enter the cerebellum by the ipsilateral inferior cerebellar peduncle in the cuneocerebellar tract. A group of neurones, nucleus Z, identified in animals between the upper pole of the nucleus gracilis and the inferior vestibular nucleus, is said to be present in the human medulla. Its input is probably from the dorsal spinocerebellar tract, which carries proprioceptive information from the ipsilateral lower limb, and it projects through internal arcuate fibres to the contralateral medial lemniscus.

Trigeminal sensory nucleus

The trigeminal sensory nucleus receives the primary afferents of the trigeminal nerve. It is a large nucleus, and extends caudally into the cervical spinal cord and rostrally into the midbrain. The principal and largest division of the nucleus is located in the pontine tegmentum.

On entering the pons, the fibres of the sensory root of the trigeminal nerve run dorsomedially towards the principal sensory nucleus, which is situated at this level (Fig. 19.9). Before reaching the nucleus approximately 50% of the fibres divide into ascending and descending branches – the others ascend or descend without division. The descending fibres, of which 90% are less than 4 μm in diameter, form the spinal tract of the trigeminal nerve, which reaches the upper cervical spinal cord. The tract embraces the nucleus of the spinal tract of the trigeminal (spinal trigeminal nucleus; Fig. 19.4, Fig. 19.5, Fig. 19.6, Fig. 19.10, Fig. 19.11). There is a precise somatotopic organization in the tract. Fibres from the ophthalmic division of the trigeminal lie ventrolaterally, those from the mandibular division lie dorsomedially, and the maxillary fibres lie between them. The tract is completed on its dorsal rim by fibres from the sensory roots of the facial, glossopharyngeal and vagus nerves. All of these fibres synapse in the nucleus caudalis.

Fig. 19.9 Transverse section of the pons at the level of the trigeminal nerve.

Fig. 19.10 Transverse section through the superior half of the medulla oblongata at the level of the inferior olivary nucleus.

Fig. 19.11 Transverse section through the pons at the level of the facial colliculus.

The detailed anatomy of the spinal tract of the trigeminal excited early clinical interest because it was recognized that dissociated sensory loss could occur in the trigeminal area. For example, in Wallenberg's syndrome, occlusion of the posterior inferior cerebellar branch of the vertebral artery leads to loss of pain and temperature sensation in the ipsilateral half of the face with retention of common sensation. Neurosurgery in this region, as early as the 1890s, attempted to alleviate paroxysmal trigeminal neuralgia. The introduction of medullary tractotomy confirmed that dissociated thermoanalgesia of the face was associated with destruction of the tract.

There are conflicting opinions on the pattern of termination of the fibres in the spinal nucleus. It has long been held that fibres are organized rostrocaudally within the tract. According to this view, ophthalmic fibres are ventral and descend to the lower limit of the first cervical spinal segment, maxillary fibres are central and do not extend below the medulla oblongata, whilst mandibular fibres are dorsal and do not extend much below the mid-medullary level. The results of section of the spinal tract in cases of severe trigeminal neuralgia support this distribution. It was found that a section 4 mm below the obex rendered the ophthalmic and maxillary areas analgesic but tactile sensibility, apart from the abolition of ‘tickle', was much less affected. To include the mandibular area it was necessary to section at the level of the obex. More recently, it has been proposed that fibres are arranged dorsoventrally within the spinal tract. There appear to be sound anatomico-physiological and clinical reasons for believing that all divisions terminate throughout the whole nucleus, although the ophthalmic division may not project fibres as far caudally as the maxillary and mandibular divisions. Fibres from the posterior face (adjacent to C2) terminate in the lower (caudal) part, whilst those from the upper lip, mouth and nasal tip terminate at a higher level. This can give rise to a segmental (cross-divisional) sensory loss in syringobulbia. Tractotomy of the spinal tract, if carried out at a lower level, can spare the perioral region, a finding that would accord with the ‘onion-skin’ pattern of loss of pain sensation. However, in clinical practice, the progression of anaesthesia on the face is most commonly ‘divisional’ rather than onion-skin in distribution.

Fibres of the glossopharyngeal, vagus and facial nerves subserving common sensation (general visceral afferent) form a column dorsally within the spinal tract of the trigeminal nerve and synapse with cells in the lowest part of the spinal trigeminal nucleus. Consequently, operative section of the dorsal part of the spinal tract results in analgesia that extends to the mucosa of the tonsillar sinus, the posterior third of the tongue and adjoining parts of the pharyngeal wall (glossopharyngeal nerve), and the cutaneous area supplied by the auricular branch of the vagus.

Other afferents that reach the spinal nucleus are from the dorsal roots of the upper cervical nerves and from the sensorimotor cortex.

The spinal nucleus is considered to consist of three parts: the subnucleus oralis (which is most rostral and adjoins the principal sensory nucleus); the subnucleus interpolaris; and the subnucleus caudalis (which is the most caudal part and is continuous below with the dorsal grey column of the spinal cord). The structure of the subnucleus caudalis is different from that of the other subnuclei. It has a structure analogous to that of the dorsal horn of the spinal cord, with a similar arrangement of cell laminae, and is involved in trigeminal pain perception. Cutaneous nociceptive afferents and small-diameter muscle afferents terminate in layers I, II, V and VI of the subnucleus caudalis. Low-threshold mechanosensitive afferents of Aβ neurones terminate in layers III and IV of the subnucleus caudalis and rostral (interpolaris, oralis and main sensory) nuclei.

Many of the neurones in the subnucleus caudalis that respond to cutaneous or tooth-pulp stimulation are also excited by stimulation of jaw or tongue muscles. This indicates that convergence of superficial and deep afferent inputs via wide-dynamic-range or nociceptive-specific neurones occurs in the nucleus. Similar convergence of superficial and deep inputs occurs in the rostral nuclei and may account for the poor localization of trigeminal pain, and for the spread of pain, which often makes diagnosis difficult.

There are distinct subtypes of cells in lamina II. Afferents from ‘higher-centres’ arborize within it, as do axons from nociceptive and low-threshold afferents. Descending influences from these higher centres include fibres from the periaqueductal grey matter and from the nucleus raphe magnus and associated reticular formation.

The nucleus raphe magnus projects directly to the subnucleus caudalis, probably via enkephalin, noradrenaline and 5-HT-containing terminals. These fibres directly or indirectly (through local interneurones) influence pain perception. Stimulation of periaqueductal grey matter or nucleus raphe magnus inhibits the jaw opening reflex to nociception, and may induce primary afferent depolarization in tooth-pulp afferents and other nociceptive facial afferents. Neurones in the subnucleus caudalis can be suppressed by stimuli applied outside their receptive field, particularly by noxious stimuli. The subnucleus caudalis is an important site for relay of nociceptive input and functions as part of the pain ‘gate-control'. However, rostral nuclei also have a nociceptive role. Tooth-pulp afferents via wide-dynamic-range and nociceptive-specific neurones may terminate in rostral nuclei, which all project to the subnucleus caudalis.

Most fibres arising in the trigeminal sensory nuclei cross the midline and ascend in the trigeminal lemniscus. They end in the contralateral thalamic nucleus ventralis posterior medialis, from which third-order neurones project to the cortical postcentral gyrus (areas 1, 2 and 3). However, some trigeminal nucleus efferents ascend to the nucleus ventralis posterior medialis of the ipsilateral thalamus.

Fibres from the subnucleus caudalis, especially from laminae I, V and VI, also project to the rostral trigeminal nuclei, cerebellum, periaqueductal grey of the midbrain, parabrachial area of the pons, the brain stem reticular formation and the spinal cord. Fibres from lamina I project to the subnucleus medius of the medial thalamus.

Vagal nucleus

The vagal nucleus (also known as the dorsal motor nucleus of the vagus) lies dorsolateral to the hypoglossal nucleus, from which it is separated by the nucleus intercalatus. It extends caudally to the first cervical spinal segment and rostrally to the open part of the medulla under the vagal triangle of the floor of the fourth ventricle (Fig. 19.6).

The vagal nucleus is a general visceral efferent nucleus and is the largest parasympathetic nucleus in the brain stem. Most (80%) of its neurones give rise to the preganglionic parasympathetic fibres of the vagus nerve. The remainder are interneurones or project centrally. The vagal nucleus controls the non-striated muscle of the viscera of the thorax (heart, bronchi, lungs and oesophagus) and abdomen (stomach, liver, pancreas, spleen, small intestine and proximal part of the colon). Neurones within the nucleus are heterogeneous and can be classified into nine subnuclei, which are regionally grouped into rostral, intermediate and caudal divisions. Topographic maps of visceral representation in animals suggest that the heart and lungs are represented in the caudal and lateral part of the nucleus, the stomach and pancreas in intermediate regions, and the remaining abdominal organs in the rostral and medial part of the nucleus.

There may be a sparse sensory afferent supply, which arises in the nodose ganglion and projects directly to the nucleus and possibly beyond into the nucleus tractus solitarius.

Hypoglossal nucleus

The prominent hypoglossal nucleus lies near the midline in the dorsal medullary grey matter. It is approximately 2 cm long. Its rostral part lies beneath the hypoglossal triangle in the floor of the fourth ventricle (Fig. 19.3) and its caudal part extends into the closed part of the medulla.

The hypoglossal nucleus consists of large motor neurones interspersed with myelinated fibres. It is organized into dorsal and ventral nuclear tiers, each divisible into medial and lateral subnuclei. There is a musculotopic organization of motor neurones within the nuclei that corresponds to the structural and functional divisions of tongue musculature. Thus, motor neurones innervating tongue retrusor muscles are located in dorsal/dorsolateral subnuclei, whereas motor neurones innervating the main tongue protrusor muscle are located in ventral/ventromedial regions of the nucleus. Although relatively little is known about the organization of motor neurones innervating the intrinsic muscles of the tongue, experimental evidence suggests that motor neurones of the medial division of the hypoglossal nucleus innervate tongue muscles that are oriented in planes transverse to the long axis of the tongue (transverse and vertical intrinsics and genioglossus), whereas motor neurones of the lateral division innervate tongue muscles that are oriented parallel to this axis (styloglossus, hyoglossus, superior and inferior longitudinal).

Several smaller groups of cells lie near the hypoglossal nucleus (perihypoglossal nuclei), but none is known for certainty to be connected with the hypoglossal nerve or nucleus. They include the nucleus intercalatus, sublingual nucleus, nucleus prepositus hypoglossi and nucleus paramedianus dorsalis (reticularis). Gustatory and visceral connections are attributed to the nucleus intercalatus.

Hypoglossal fibres emerge ventrally from their nucleus, traverse the reticular formation lateral to the medial lemniscus, pass medial to (sometimes through) the inferior olivary nucleus, and curve laterally to emerge as a linear series of 10–15 rootlets in the ventrolateral sulcus between the pyramid and olive.

The hypoglossal nucleus receives corticobulbar fibres from the precentral gyrus and adjacent areas of (mainly) the contralateral hemisphere. They either synapse on motor neurones of the nucleus directly or on interneurones. Evidence indicates that the most medial hypoglossal subnuclei receive projections from both hemispheres. The nucleus may connect with the cerebellum via adjacent perihypoglossal nuclei, and perhaps also with the medullary reticular formation, the trigeminal sensory nuclei and the solitary nucleus.

Inferior olivary nucleus

The olivary nuclear complex consists of the large inferior olivary nucleus and the much smaller medial accessory and dorsal accessory olivary nuclei (Fig. 19.6). They are the so-called precerebellar nuclei, a group that also includes the pontine, arcuate, vestibular, reticulocerebellar and spinocerebellar nuclei, all of which receive afferents from specific sources and project to the cerebellum. The inferior olivary nucleus contains small neurones, most of which form the olivocerebellar tract, which emerges either from the hilum or through the adjacent grey matter, to run medially and intersect the medial lemniscus (Fig. 19.6). Its fibres cross the midline, and sweep either dorsal to, or through, the opposite olivary nucleus. They intersect the lateral spinothalamic and rubrospinal tracts and the spinal trigeminal nucleus, and enter the contralateral inferior cerebellar peduncle, where they constitute its major component. Fibres from the contralateral inferior olivary complex terminate on Purkinje cells in the cerebellum as climbing fibres – there is a one-to-one relationship between Purkinje cells and neurones in the complex. Afferent connections to the inferior olivary nucleus are both ascending and descending. Ascending fibres, mainly crossed, arrive from all spinal levels in the spino-olivary tracts and via the dorsal columns. Descending ipsilateral fibres come from the cerebral cortex, thalamus, red nucleus and central grey of the midbrain. In part the two latter projections make up the central tegmental tract (fasciculus).

The medial accessory olivary nucleus is a curved grey lamina, concave laterally, between the medial lemniscus and pyramid and the ventromedial aspect of the inferior olivary nucleus. The dorsal accessory olivary nucleus is a similar lamina, dorsomedial to the inferior olivary nucleus. Both nuclei are connected to the cerebellum. The accessory olivary nuclei are phylogenetically older than the inferior olivary nucleus, and they are connected with the paleocerebellum. In all connections, cerebral, spinal and cerebellar, the olivary nuclei display specific topographical organization (Ch. 20).

Nucleus solitarius

The nucleus solitarius (solitary nucleus, nucleus of the solitary tract) lies ventrolateral to the vagal nucleus and is almost coextensive with it. A neuronal group ventrolateral to the nucleus solitarius has been termed the nucleus parasolitarius. The nucleus solitarius is intimately related to, and receives fibres from, the tractus solitarius, which carries afferent fibres from the facial, glossopharyngeal and vagus nerves. These fibres enter the tract in descending order and convey gustatory information from the lingual and palatal mucosa. They may also convey visceral impulses from the pharynx (glossopharyngeal and vagus) and from the oesophagus and abdominal alimentary canal (vagus). There is some overlap in this vertical representation.

Termination of special visceral gustatory afferents within the nucleus shows a viscerotopic pattern, predominantly in the rostral region. Experimental evidence suggests that fibres from the anterior two-thirds of the tongue and the roof of the oral cavity (which travel via the chorda tympani and greater petrosal branches of the facial nerve) terminate in the extreme rostral part of the solitary complex. Those from the circumvallate and foliate papillae of the posterior third of the tongue, tonsils, palate and pharynx (which travel via the lingual branch of the glossopharyngeal nerve) are distributed throughout the rostrocaudal extent of the nucleus, predominantly rostral to the obex. Gustatory afferents from the larynx and epiglottis (which travel via the superior laryngeal branch of the vagus) have a more caudal and lateral distribution. The nucleus solitarius may also receive fibres from the spinal cord, cerebral cortex and cerebellum.

Medial and commissural subnuclei in the caudal part of the nucleus appear to be the primary site of termination for gastrointestinal afferents. Ventral and interstitial subnuclei probably receive tracheal, laryngeal and pulmonary afferents and play an important role in both respiratory control and possibly rhythm generation. The carotid sinus and aortic body nerves terminate in the dorsal and dorsolateral region of the nucleus solitarius, which may be involved in cardiovascular regulation.

The nucleus solitarius is thought to project to the sensory thalamus and thence to the cerebral cortex. It may also project to the upper levels of the spinal cord through a solitariospinal tract. Secondary gustatory axons cross the midline. Many subsequently ascend the brain stem in the dorsomedial part of the medial lemniscus and synapse on the most medial neurones of the thalamic nucleus ventralis posterior medialis (in a region sometimes termed the accessory arcuate nucleus). Axons from the nucleus ventralis posterior medialis radiate through the internal capsule to the anteroinferior area of the sensorimotor cortex and the insula. It is thought that other ascending paths end in a number of the hypothalamic nuclei, and so mediate the route by which gustatory information may reach the limbic system and allow appropriate autonomic reactions to be made.

Swallowing and gag reflexes

During the normal processes of eating and drinking, passage of material to the rear of the mouth stimulates branches of the glossopharyngeal nerve in the oropharynx (Fig. 19.12). This information is relayed via the nucleus solitarius to the nucleus ambiguus, which contains the motor neurones innervating the muscles of the palate, pharynx, and larynx. The nasopharynx is closed off from the oropharynx by elevation of the soft palate. The larynx is raised, its entrance narrowed and the glottis is closed. Peristaltic activity down the oesophagus to the stomach is mediated through the pharyngeal plexus.

Fig. 19.12 Swallowing and gag reflexes.

If stimulation of the oropharynx occurs, other than during swallowing, the gag reflex may be initiated. There is a reflex contraction of the muscles of the pharynx, soft palate, and fauces that, if extreme, may result in retching and vomiting.

Nucleus ambiguus

The nucleus ambiguus is a group of large motor neurones, situated deep in the medullary reticular formation (see Fig. 19.10). It extends rostrally as far as the upper end of the vagal nucleus while caudally it is continuous with the nucleus of the spinal accessory nerve. Fibres emerging from it pass dorsomedially, then curve laterally. Rostral fibres join the glossopharyngeal nerve. Caudal fibres join the vagus and cranial accessory nerves and are distributed to the pharyngeal constrictors, intrinsic laryngeal muscles and striated muscles of the palate and upper oesophagus.

The nucleus ambiguus contains several cellular subgroups, and some topographical representation of the muscles innervated has been established. Individual laryngeal muscles are innervated by relatively discrete groups of cells in more caudal zones. Neurones that innervate the pharynx lie in the intermediate area, and neurones that innervate the oesophagus and soft palate are rostral.

The nucleus ambiguus receives corticobulbar fibres bilaterally and is connected to many brain stem centres. At its upper end, a small retrofacial nucleus intervenes between it and the facial nucleus. Although the nucleus ambiguus is generally regarded as a special visceral efferent nucleus, it is also a reputed source of general visceral efferent fibres to the vagus.

Cough and sneeze reflexes

Irritation of the larynx or trachea is conveyed via laryngeal branches of the vagus nerve to the trigeminal sensory nucleus of the brain stem. Impulses are relayed to medullary respiratory centres and to the nucleus ambiguus. Forceful exhalation (coughing) occurs, caused by contraction of intercostal and abdominal wall muscles after a build-up of pressure against an initially closed glottis.

A similar mechanism underlies sneezing (Fig. 19.13) except that the stimulus arises from the nasal mucosa and afferent impulses are conveyed by the ophthalmic or maxillary divisions of the trigeminal nerve to the trigeminal sensory nucleus. After sharp inhalation, explosive exhalation occurs with closure of the oropharyngeal isthmus by the action of palatoglossus, which diverts air through the nasal cavity.

Fig. 19.13 Sneeze and cough reflexes.

 

 

 

The Maxillary Nerve (n. maxillaris; superior maxillary nerve) (778), or second division of the trigeminal, is a sensory nerve. It is intermediate, both in position and size, between the ophthalmic and mandibular. It begins at the middle of the semilunar ganglion as a flattened plexiform band, and, passing horizontally forward, it leaves the skull through the foramen rotundum, where it becomes more cylindrical in form, and firmer in texture. It then crosses the pterygopalatine fossa, inclines lateralward on the back of the maxilla, and enters the orbit through the inferior orbital fissure; it traverses the infraorbital groove and canal in the floor of the orbit, and appears upon the face at the infraorbital foramen. 131 At its termination, the nerve lies beneath the Quadratus labii superioris, and divides into a leash of branches which spread out upon the side of the nose, the lower eyelid, and the upper lip, joining with filaments of the facial nerve.

 

Branches.—Its branches may be divided into four groups, according as they are given off in the cranium, in the pterygopalatine fossa, in the infraorbital canal, or on the face.

In the Cranium……………

Middle meningeal.

In the Pterygopalatine Fossa…

Zygomatic.

Sphenopalatine.

Posterior superior alveolar.

In the Infraorbital Canal………

Anterior superior alveolar.

Middle superior alveolar.

On the Face…………………

Inferior palpebral.

External nasal.

Superior labial.

  The Middle Meningeal Nerve (n. meningeus medius; meningeal or dural branch) is given off from the maxillary nerve directly after its origin from the semilunar ganglion; it accompanies the middle meningeal artery and supplies the dura mater.

  The Zygomatic Nerve (n. zygomaticus; temporomalar nerve; orbital nerve) arises in the pterygopalatine fossa, enters the orbit by the inferior orbital fissure, and divides at the back of that cavity into two branches, zygomaticotemporal and zygomaticofacial.

  The zygomaticotemporal branch (ramus zygomaticotemporalis; temporal branch) runs along the lateral wall of the orbit in a groove in the zygomatic bone, receives a branch of communication from the lacrimal, and, passing through a foramen in the zygomatic bone, enters the temporal fossa. It ascends between the bone, and substance of the Temporalis muscle, pierces the temporal fascia about 2.5 cm. above the zygomatic arch, and is distributed to the skin of the side of the forehead, and communicates with the facial nerve and with the aurićulotemporal branch of the mandibular nerve. As it pierces the temporal fascia, it gives off a slender twig, which runs between the two layers of the fascia to the lateral angle of the orbit.

  The zygomaticofacial branch (ramus zygomaticofacialis; malar branch) passes along the infero-lateral angle of the orbit, emerges upon the face through a foramen in the zygomatic bone, and, perforating the Orbicularis oculi, supplies the skin on the prominence of the cheek. It joins with the facial nerve and with the inferior palpebral branches of the maxillary.

  The Sphenopalatine Branches (nn. sphenopalatini), two in number, descend to the sphenopalatine ganglion.

  The Posterior Superior Alveolar Branches (rami alveolares superiores posteriores; posterior superior dental branches) arise from the trunk of the nerve just before it enters the infraorbital groove; they are generally two in number, but sometimes arise by a single trunk. They descend on the tuberosity of the maxilla and give off several twigs to the gums and neighboring parts of the mucous membrane of the cheek. They then enter the posterior alveolar canals on the infratemporal surface of the maxilla, and, passing from behind forward in the substance of the bone, communicate with the middle superior alveolar nerve, and give off branches to the lining membrane of the maxillary sinus and three twigs to each molar tooth; these twigs enter the foramina at the apices of the roots of the teeth.

  The Middle Superior Alveolar Branch (ramus alveolaris superior medius; middle superior dental branch), is given off from the nerve in the posterior part of the infraorbital canal, and runs downward and forward in a canal in the lateral wall of the maxillary sinus to supply the two premolar teeth. It forms a superior dental plexus with the anterior and posterior superior alveolar branches.

  The Anterior Superior Alveolar Branch (ramus alveolaris superior anteriores; anterior superior dental branch), of considerable size, is given off from the nerve just before its exit from the infraorbital foramen; it descends in a canal in the anterior wall of the maxillary sinus, and divides into branches which supply the incisor and canine teeth. It communicates with the middle superior alveolar branch, and gives off a nasal branch, which passes through a minute canal in the lateral wall of the inferior meatus, and supplies the mucous membrane of the anterior part of the inferior meatus and the floor of the nasal cavity, communicating with the nasal branches from the sphenopalatine ganglion.

Alveolar branches of superior maxillary nerve and sphenopalatine ganglion.

 

  The Inferior Palpebral Branches (rami palpebrales inferiores; palpebral branches) ascend behind the Orbicularis oculi. They supply the skin and conjunctiva of the lower eyelid, joining at the lateral angle of the orbit with the facial and zygomaticofacial nerves.

  The External Nasal Branches (rami nasales externi) supply the skin of the side of the nose and of the septum mobile nasi, and join with the terminal twigs of the nasociliary nerve.

  The Superior Labial Branches (rami labiales superiores; labial branches), the largest and most numerous, descend behind the Quadratus labii superioris, and are distributed to the skin of the upper lip, the mucous membrane of the mouth, and labial glands. They are joined, immediately beneath the orbit, by filaments from the facial nerve, forming with them the infraorbital plexus.

 

Sphenopalatine Ganglion (ganglion of Meckel) (780).

 

—The sphenopalatine ganglion, the largest of the sympathetic ganglia associated with the branches of the trigeminal nerve, is deeply placed in the pterygopalatine fossa, close to the sphenopalatine foramen. It is triangular or heart-shaped, of a reddish-gray color, and is situated just below the maxillary nerve as it crosses the fossa. It receives a sensory, a motor, and a sympathetic root.

  Its sensory root is derived from two sphenopalatine branches of the maxillary nerve; their fibers, for the most part, pass directly into the palatine nerves; a few, however, enter the ganglion, constituting its sensory root. Its motor root is probably derived from the nervus intermedius through the greater superficial petrosal nerve and is supposed to consist in part of sympathetic efferent (preganglionic) fibers from the medulla. In the sphenopalatine ganglion they form synapses with neurons whose postganglionic axons, vasodilator and secretory fibers, are distributed with the deep branches of the trigeminal to the mucous membrane of the nose, soft palate, tonsils, uvula, roof of the mouth, upper lip and gums, and to the upper part of the pharynx. Its sympathetic root is derived from the carotid plexus through the deep petrosal nerve. These two nerves join to form the nerve of the pterygoid canal before their entrance into the ganglion.

The sphenopalatine ganglion and its branches.

 

  The greater superficial petrosal nerve (n. petrosus superficialis major; large superficial petrosal nerve) is given off from the genicular ganglion of the facial nerve; it passes through the hiatus of the facial canal, enters the cranial cavity, and runs forward beneath the dura mater in a groove on the anterior surface of the petrous portion of the temporal bone. It then enters the cartilaginous substance which fills the foramen lacerum, and joining with the deep petrosal branch forms the nerve of the pterygoid canal.

  The deep petrosal nerve (n. petrosus profundus; large deep petrosal nerve) is given off from the carotid plexus, and runs through the carotid canal lateral to the internal carotid artery. It then enters the cartilaginous substance which fills the foramen lacerum, and joins with the greater superficial petrosal nerve to form the nerve of the pterygoid canal.

  The nerve of the pterygoid canal (n. canalis pterygoidei [Vidii]; Vidian nerve), formed by the junction of the two preceding nerves in the cartilaginous substance which fills the foramen lacerum, passes forward, through the pterygoid canal, with the corresponding artery, and is joined by a small ascending sphenoidal branch from the otic ganglion. Finally, it enters the pterygopalatine fossa, and joins the posterior angle of the sphenopalatine ganglion.

 

Branches of Distribution.—These are divisible into four groups, viz., orbital, palatine, posterior superior nasal, and pharyngeal.

  The orbital branches (rami orbitales; ascending branches) are two or three delicate filaments, which enter the orbit by the inferior orbital fissure, and supply the periosteum. According to Luschka, some filaments pass through foramina in the frontoethmoidal suture to supply the mucous membrane of the posterior ethmoidal and sphenoidal sinuses.

  The palatine nerves (nn. palatini; descending branches) are distributed to the roof of the mouth, soft palate, tonsil, and lining membrane of the nasal cavity. Most of their fibers are derived from the sphenopalatine branches of the maxillary nerve. They are three in number: anterior, middle, and posterior.

  The anterior palatine nerve (n. palatinus anterior) descends through the pterygopalatine canal, emerges upon the hard palate through the greater palatine foramen, and passes forward in a groove in the hard palate, nearly as far as the incisor teeth. It supplies the gums, the mucous membrane and glands of the hard palate, and communicates in front with the terminal filaments of the nasopalatine nerve. While in the pterygopalatine canal, it gives off posterior inferior nasal branches, which enter the nasal cavity through openings in the palatine bone, and ramify over the inferior nasal concha and middle and inferior meatuses; at its exit from the canal, a palatine branch is distributed to both surfaces of the soft palate.

  The middle palatine nerve (n. palatinus medius) emerges through one of the minor palatine canals and distributes branches to the uvula, tonsil, and soft palate. It is occasionally wanting.

  The posterior palatine nerve (n. palatinus posterior) descends through the pterygopalatine canal, and emerges by a separate opening behind the greater palatine foramen; it supplies the soft palate, tonsil, and uvula. The middle and posterior palatine join with the tonsillar branches of the glossopharyngeal to form a plexus (circulus tonsillaris) around the tonsil.

  The posterior superior nasal branches (rami nasales posteriores superiores) are distributed to the septum and lateral wall of the nasal fossa. They enter the posterior part of the nasal cavity by the sphenopalatine foramen and supply the mucous membrane covering the superior and middle nasal conchæ, the lining of the posterior ethmoidal cells, and the posterior part of the septum. One branch, longer and larger than the others, is named the nasopalatine nerve. It enters the nasal cavity through the sphenopalatine foramen, passes across the roof of the nasal cavity below the orifice of the sphenoidal sinus to reach the septum, and then runs obliquely downward and forward between the periosteum and mucous membrane of the lower part of the septum. It descends to the roof of the mouth through the incisive canal and communicates with the corresponding nerve of the opposite side and with the anterior palatine nerve. It furnishes a few filaments to the mucous membrane of the nasal septum.

  The pharyngeal nerve (pterygopalatine nerve) is a small branch arising from the posterior part of the ganglion. It passes through the pharyngeal canal with the pharyngeal branch of the internal maxillary artery, and is distributed to the mucous membrane of the nasal part of the pharynx, behind the auditory tube.

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Theme 2. the 3-d division of of the fifth cranial nerve, areas of distribution. Autonomic ganglia of the head

Mandibular nerve carries both the motor and sensory fibres. After passing out from ovale foramen mandibular nerve gives off the motor branches that innervate all 4 masticatory muscles, also velli palatine tensor muscle and nerve tensor of tympanic membrane muscle. Sensory branches of the mandibular nerve: buccal nerve, auriculotemporal nerve, lingual nerve infeior alveolar nerve and meningeal branches.

Buccal nerve transfixes a buccinator muscle and innervates mucous membrane of the cheek and also mouth corner skin.

Auriculotemporal nerve begins by two rootlets that envelop a middle meningeal artery, and then unite into one trunk, which transfixes parotid gland, innervating it and skin of temporal area, also, the auricle. Postganglionic parasympathetic fibres from otic ganglion pass in composition of this nerve, which provide a secretory innervation of parotid gland.

Lingual nerve passes on internal surface of lower jaw under mucous membrane of the mouth cavity and enters into lower part of tongue, providing a general sensory innervation of the anterior 2/3 part and sensory innervation sublingual and submandibular salivary glands. Chorda tympani (from 7th cranial nerve), which contains the gustatory (tasting) and secretory (parasympathetic) fibres. Gustatory fibres innervate of tasting buds on mucous membrane of the anterior 2/3 part of the tongue, and secretory (parasympathetic) enter in to submandibular and sublingual parasympatheticих ganglia. The postganglionic fibres from these ganglia provide a secretory innervation the same name - submandibular and sublingual salivary glands.

Inferior alveolar nerve (mixed) has a motor branches that supply mylo-hyoid muscle and anterior belly of the digastric muscle. The sensory fibres enter into mandibular channel, where form inferior dental plexus, branches innervate the teeth and gums of lower jaw. From canal these fibres are passing out from bone as a mental nerve, which terminates in skin of lower lip and chin.

  The mandibular nerve (n. mandibulari supplies the teeth and gums of the mandible, the skin of the temporal region, the auricula, the lower lip, the lower part of the face, and the muscles of mastication; it also supplies the mucous membrane of the anterior two-thirds of the tongue. It is the largest of the three divisions of the fifth, and is made up of two roots: a large, sensory root proceeding from the inferior angle of the semilunar ganglion, and a small motor root (the motor part of the trigeminal), which passes beneath the ganglion, and unites with the sensory root, just after its exit through the foramen ovale. Immediately beneath the base of the skull, the nerve gives off from its medial side a recurrent branch (nervus spinosus) and the nerve to the Pterygoideus internus, and then divides into two trunks, an anterior and a posterior.

  The Nervus Spinosus (recurrent or meningeal branch) enters the skull through the foramen spinosum with the middle meningeal artery. It divides into two branches, anterior and posterior, which accompany the main divisions of the artery and supply the dura mater; the posterior branch also supplies the mucous lining of the mastoid cells; the anterior communicates with the meningeal branch of the maxillary nerve.

Mandibular division of the trifacial nerve.

  INNERVATION

The numerous muscles of facial expression are supplied by the facial nerve, while the two muscles of mastication that relate to the face are innervated by the mandibular division of the trigeminal nerve. The sensory innervation is primarily from the three divisions of the trigeminal nerve, with smaller contributions from the cervical spinal nerves. The detailed innervation of the auricle is considered on p. 620.

TRIGEMINAL NERVE

Three large areas of the face can be mapped out to indicate the peripheral nerve fields associated with the three divisions of the trigeminal nerve. The fields are not horizontal but curve upwards (Fig. 29.15), apparently because the facial skin moves upwards with growth of the brain and skull. Embryologically, each division of the trigeminal nerve is associated with a developing facial process which gives rise to a specific area of the adult face: the ophthalmic nerve is associated with the frontonasal process, the maxillary nerve with the maxillary process, and the mandibular nerve with the mandibular process.

Fig. 29.15 Cutaneous innervation of the face and neck, showing dermatomes (in bold). (Adapted from Drake, Vogl and Mitchell 2005.)

Ophthalmic nerve

The cutaneous branches of the ophthalmic nerve supply the conjunctiva, skin over the forehead, upper eyelid and much of the external surface of the nose.

Supratrochlear nerve

The supratrochlear nerve is the smaller terminal branch of the frontal nerve. It runs anteromedially in the roof of the orbit, passes above the trochlea, and supplies a descending filament to the infratrochlear branch of the nasociliary nerve. The nerve emerges between the trochlea and the supraorbital foramen at the frontal notch, curves up on the forehead close to the bone with the supratrochlear artery and supplies the conjunctiva and the skin of the upper eyelid. It then ascends beneath the corrugator and the frontal belly of occipitofrontalis before dividing into branches which pierce these muscles to supply the skin of the lower forehead near the midline.

Supraorbital nerve

The supraorbital nerve is the larger terminal branch of the frontal nerve. It traverses the supraorbital notch or foramen and supplies palpebral filaments to the upper eyelid and conjunctiva. It ascends on the forehead with the supraorbital artery, and divides into medial and lateral branches which supply the skin of the scalp nearly as far back as the lambdoid suture. These branches are at first deep to the frontal belly of occipitofrontalis. The medial branch perforates the muscle to reach the skin, while the lateral branch pierces the epicranial aponeurosis.

Lacrimal nerve

The lacrimal nerve is the smallest of the main ophthalmic branches and pierces the orbital septum to end in the lateral region of the upper eyelid, which it supplies. It anastomoses with filaments of the facial nerve. Occasionally it is absent, in which case it is replaced by the zygomaticotemporal nerve: the relationship is reciprocal, and when the zygomaticotemporal nerve is absent it is replaced by a branch of the lacrimal nerve.

Infratrochlear nerve

The infratrochlear nerve branches from the nasociliary nerve. It leaves the orbit below the trochlea and supplies the skin of the eyelids, the conjunctiva, lacrimal sac, lacrimal caruncle and the side of the nose above the medial canthus.

External nasal nerve

The external nasal nerve is the terminal branch of the anterior ethmoidal nerve. It descends through the lateral wall of the nose, and supplies the skin of the nose below the nasal bones, excluding the alar portion around the external nares.

Maxillary nerve

The maxillary nerve passes through the orbit to supply the skin of the lower eyelid, the prominence of the cheek, the alar part of the nose, part of the temple, and the upper lip. It has three cutaneous branches, the zygomaticotemporal, zygomaticofacial and infraorbital nerves.

Zygomaticotemporal nerve

The zygomaticotemporal nerve traverses a canal in the zygomatic bone and emerges into the anterior part of the temporal fossa, where it ascends between the bone and temporalis before piercing the temporal fascia about 2 cm above the zygomatic arch to supply the skin of the temple. It communicates with the facial and auriculotemporal nerves. As it pierces the deep layer of the temporal fascia it sends a slender twig between the two layers of the fascia towards the lateral angle of the eye: the branch carries parasympathetic postganglionic fibres from the pterygopalatine ganglion to the lacrimal gland.

Zygomaticofacial nerve

The zygomaticofacial nerve traverses the inferolateral angle of the orbit, and emerges on the face through a foramen in the zygomatic bone. It perforates orbicularis oculi to supply the skin on the prominence of the cheek and forms a plexus with zygomatic branches of the facial nerve and palpebral branches of the maxillary nerve. Occasionally the nerve is absent.

Infraorbital nerve

The infraorbital nerve emerges onto the face at the infraorbital foramen, where it lies between levator labii superioris and levator anguli oris. It gives off palpebral, nasal and superior labial branches. The palpebral branches ascend deep to orbicularis oculi, pierce the muscle to supply the skin in the lower eyelid and join with the facial and zygomaticofacial nerves near the lateral canthus. Nasal branches supply the skin of the side of the nose and of the movable part of the nasal septum, and join the external nasal branch of the anterior ethmoidal nerve. Superior labial branches, which are large and numerous, descend behind levator labii superioris to supply the skin of the anterior part of the cheek and upper lip. They are joined by branches from the facial nerve to form the infraorbital plexus. The infraorbital nerve is commonly implicated in trigeminal neuralgia, and is amenable to cryotherapy where medical therapy fails.

Mandibular nerve

The mandibular nerve supplies skin over the mandible, the lower lip, the fleshy part of the cheek, part of the auricle of the ear and part of the temple via the buccal, mental and auriculotemporal nerves.

Buccal nerve

The buccal nerve emerges onto the face from behind the ramus of the mandible and passes laterally in front of masseter to unite with the buccal branches of the facial nerve. It supplies the skin over the anterior part of buccinator.

Mental nerve

The mental nerve is the terminal branch of the inferior alveolar nerve (see Ch. 30). It enters the face through the mental foramen, where it is directed backwards, and supplies the skin of the lower lip and labial gingivae. Occasionally the mental nerve is important aetiologically in the pain of trigeminal neuralgia, and it is amenable to cryotherapy surgery.

Auriculotemporal nerve

The auriculotemporal nerve emerges onto the face behind the temporomandibular joint within the superior surface of the parotid gland. It ascends posterior to the superficial temporal vessels, passes over the posterior root of the zygoma, and divides into superficial temporal branches. The cutaneous branches of the auriculotemporal nerve supply the tragus and part of the adjoining auricle of the ear and the posterior part of the temple. The nerve may be damaged during parotid gland surgery resulting in impaired sensation of the tragus and temple. It communicates with the temporofacial division of the facial nerve, usually by two rami that pass anterolaterally behind the neck of the mandible. These communications anchor the facial nerve close to the lateral surface of the condylar process of the mandible, and limit its mobility during surgery. Communications with the temporal and zygomatic branches of the facial nerve loop around the transverse facial and superficial temporal vessels.

 

The Internal Pterygoid Nerve (n. pterygoideus internus).—The nerve to the Pterygoideus internus is a slender branch, which enters the deep surface of the muscle; it gives off one or two filaments to the otic ganglion.

  The anterior and smaller division of the mandibular nerve receives nearly the whole of the fibers of the motor root of the nerve, and supplies the muscles of mastication and the skin and mucous membrane of the cheek. Its branches are the masseteric, deep temporal, buccinator, and external pterygoid.

  The Masseteric Nerve (n. massetericus) passes lateralward, above the Pterygoideus externus, in front of the temporomandibular articulation, and behind the tendon of the Temporalis; it crosses the mandibular notch with the masseteric artery, to the deep surface of the Masseter, in which it ramifies nearly as far as its anterior border. It gives a filament to the temporomandibular joint.

  The Deep Temporal Nerves (nn. temporales profundi) are two in number, anterior and posterior. They pass above the upper border of the Pterygoideus externus and enter the deep surface of the Temporalis. The posterior branch, of small size, is placed at the back of the temporal fossa, and sometimes arises in common with the masseteric nerve. The anterior branch is frequently given off from the buccinator nerve, and then turns upward over the upper head of the Pterygoideus externus. Frequently a third or intermediate branch is present.

  The Buccinator Nerve (n. buccinatorus; long buccal nerve) passes forward between the two heads of the Pterygoideus externus, and downward beneath or through the lower part of the Temporalis; it emerges from under the anterior border of the Masseter, ramifies on the surface of the Buccinator, and unites with the buccal branches of the facial nerve. It supplies a branch to the Pterygoideus externus during its passage through that muscle, and may give off the anterior deep temporal nerve. The buccinator nerve supplies the skin over the Buccinator, and the mucous membrane lining its inner surface.

 

External Pterygoid Nerve (n. pterygoideus externus).—The nerve to the Pterygoideus externus frequently arises in conjunction with the buccinator nerve, but it may be given off separately from the anterior division of the mandibular nerve. It enters the deep surface of the muscle.

  The posterior and larger division of the mandibular nerve is for the most part sensory, but receives a few filaments from the motor root. It divides into auriculotemporal, lingual, and inferior alveolar nerves.

  The Auriculotemporal Nerve (n. auriculotemporalis) generally arises by two roots, between which the middle meningeal artery ascends. It runs backward beneath the Pterygoideus externus to the medial side of the neck of the mandible. It then turns upward with the superficial temporal artery, between the auricula and condyle of the mandible, under cover of the parotid gland; escaping from beneath the gland, it ascends over the zygomatic arch, and divides into superficial temporal branches.

  The branches of communication of the auriculotemporal nerve are with the facial nerve and with the otic ganglion. The branches to the facial, usually two in number, pass forward from behind the neck of the mandible and join the facial nerve at the posterior border of the Masseter. The filaments to the otic ganglion are derived from the roots of the auriculotemporal nerve close to their origin.

  Its branches of distribution are:

Anterior auricular.

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Articular.

Branches to the external acoustic meatus.

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Parotid.

Superficial temporal.

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  The anterior auricular branches (nn. auriculares anteriores) are usually two in number; they supply the front of the upper part of the auricula, being distributed principally to the skin covering the front of the helix and tragus.

  The branches to the external acoustic meatus (n. meatus auditorii externi), two in number, enter the meatus between its bony and cartilaginous portions and supply the skin lining it; the upper one sends a filament to the tympanic membrane.

  The articular branches consist of one or two twigs which enter the posterior part of the temporomandibular joint.

  The parotid branches (rami parotidei) supply the parotid gland.

  The superficial temporal branches (rami temporales superficiales) accompany the superficial temporal artery to the vertex of the skull; they supply the skin of the temporal region and communicate with the facial and zygomaticotemporal nerves.

  The Lingual Nerve (n. lingualis) supplies the mucous membrane of the anterior two-thirds of the tongue. It lies at first beneath the Pterygoideus externus, medial to and in front of the inferior alveolar nerve, and is occasionally joined to this nerve by a branch which may cross the internal maxillary artery. The chorda tympani also joins it at an acute angle in this situation. The nerve then passes between the Pterygoideus internus and the ramus of the mandible, and crosses obliquely to the side of the tongue over the Constrictor pharyngis superior and Styloglossus, and then between the Hyoglossus and deep part of the submandibular gland; it finally runs across the duct of the submandibular gland, and along the tongue to its tip, lying immediately beneath the mucous membrane.

  Its branches of communication are with the facial (through the chorda tympani), the inferior alveolar and hypoglossal nerves, and the submandibular ganglion. The branches to the submandibular ganglion are two or three in number; those connected with the hypoglossal nerve form a plexus at the anterior margin of the Hyoglossus.

Mandibular division of trifacial nerve, seen from the middle line. The small figure is an enlarged view of the otic ganglion

 

  Its branches of distribution supply the sublingual gland, the mucous membrane of the mouth, the gums, and the mucous membrane of the anterior two-thirds of the tongue; the terminal filaments communicate, at the tip of the tongue, with the hypoglossal nerve.

  The Inferior Alveolar Nerve (n. alveolaris inferior; inferior dental nerve)(782) is the largest branch of the mandibular nerve. It descends with the inferior alveolar artery, at first beneath the Pterygoideus externus, and then between the sphenomandibular ligament and the ramus of the mandible to the mandibular foramen. It then passes forward in the mandibular canal, beneath the teeth, as far as the mental foramen, where it divides into two terminal branches, incisive and mental.

  The branches of the inferior alveolar nerve are the mylohyoid, dental, incisive, and mental.

  The mylohyoid nerve (n. mylohyoideus) is derived from the inferior alveolar just before it enters the mandibular foramen. It descends in a groove on the deep surface of the ramus of the mandible, and reaching the under surface of the Mylohyoideus supplies this muscle and the anterior belly of the Digastricus.

  The dental branches supply the molar and premolar teeth. They correspond in number to the roots of those teeth; each nerve entering the orifice at the point of the root, and supplying the pulp of the tooth; above the alveolar nerve they form an inferior dental plexus.

  The incisive branch is continued onward within the bone, and supplies the canine and incisor teeth.

  The mental nerve (n. mentalis) emerges at the mental foramen, and divides beneath the Triangularis muscle into three branches; one descends to the skin of the chin, and two ascend to the skin and mucous membrane of the lower lip; these branches communicate freely with the facial nerve.

  Two small ganglia, the otic and the submaxillary, are connected with the mandibular nerve.

The otic ganglion and its branches.

 

 

Otic Ganglion (ganglion oticum)(783).—The otic ganglion is a small, ovalshaped, flattened ganglion of a reddish-gray color, situated immediately below the foramen ovale; it lies on the medial surface of the mandibular nerve, and surrounds the origin of the nerve to the Pterygoideus internus. It is in relation, laterally, with the trunk of the mandibular nerve at the point where the motor and sensory roots join; medially, with the cartilaginous part of the auditory tube, and the origin of the Tensor veli palatini; posteriorly, with the middle meningeal artery.

 

Branches of Communication.—It is connected by two or three short filaments with the nerve to the Pterygoideus internus, from which it may obtain a motor, and possibly a sensory root. It communicates with the glossopharyngeal and facial nerves, through the lesser superficial petrosal nerve continued from the tympanic plexus, and through this nerve it probably receives a root from the glossopharyngeal and a motor root from the facial; its sympathetic root consists of a filament from the plexus surrounding the middle meningeal artery. The fibers from the glossopharyngeal which pass to the otic ganglion in the small superficial petrosal are supposed to be sympathetic efferent (preganglionic) fibers from the dorsal nucleus or inferior salivatory nucleus of the medulla. Fibers (postganglionic) from the otic ganglion with which these form synapses are supposed to pass with the auriculotemporal nerve to the parotid gland. A slender filament (sphenoidal) ascends from it to the nerve of the Pterygoid canal, and a small branch connects it with the chorda tympani.

  Its branches of distribution are: a filament to the Tensor tympani, and one to the Tensor veli palatini. The former passes backward, lateral to the auditory tube; the latter arises from the ganglion, near the origin of the nerve to the Pterygoideus internus, and is directed forward. The fibers of these nerves are, however, mainly derived from the nerve to the Pterygoideus internus.

Sensory areas of the head, showing the general distribution of the three divisions of the fifth nerve.

 

 

Submandibular Ganglion (ganglion submaxillare)(778).—The submandibular ganglion is of small size and is fusiform in shape. It is situated above the deep portion of the submandibular gland, on the hyoglossus, near the posterior border of the Mylohyoideus, and is connected by filaments with the lower border of the lingual nerve. It is suspended from the lingual nerve by two filaments which join the anterior and posterior parts of the ganglion. Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual; these are sympathetic efferent (preganglionic) fibers from the facial nucleus or the superior salivatory nucleus of the medulla oblongata that terminate in the submandibular ganglion. The postganglionic fibers pass to the submandibular gland, it communicates with the sympathetic by filaments from the sympathetic plexus around the external maxillary artery.

  Its branches of distribution are five or six in number; they arise from the lower part of the ganglion, and supply the mucous membrane of the mouth and the duct of the submandibular gland, some being lost in the submandibular gland. The branch of communication from the lingual to the forepart of the ganglion is by some regarded as a branch of distribution, through which filaments pass from the ganglion to the lingual nerve, and by it are conveyed to the sublingual gland and the tongue.

 

Trigeminal Nerve Reflexes.—Pains referred to various branches of the trigeminal nerve are of very frequent occurrence, and should always lead to a careful examination in order to discover a local cause. As a general rule the diffusion of pain over the various branches of the nerve is at first confined to one only of the main divisions, and the search for the causative lesion should always commence with a thorough examination of all those parts which are supplied by that division; although in severe cases pain may radiate over the branches of the other main divisions. The commonest example of this condition is the neuralgia which is so often associated with dental caries—here, although the tooth itself may not appear to be painful, the most distressing referred pains may be experienced, and these are at once relieved by treatment directed to the affected tooth.

  Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention the more common ones. Dealing with the ophthalmic nerve, severe supraorbital pain is commonly associated with acute glaucoma or with disease of the frontal or ethmoidal air cells. Malignant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior conchæ or the septum of the nose, are often found giving rise to “second division” neuralgia, and should be always looked for in the absence of dental disease in the maxilla.

  It is on the mandibular nerve, however, that some of the most striking reflexes are seen. It is quite common to meet with patients who complain of pain in the ear, in whom there is no sign of aural disease, and the cause is usually to be found in a carious tooth in the mandible. Moreover, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve.