NERVE SUPPLY OF HEAD AND NECK

Contents :Introduction to cranial nervesTrigeminal nerve in detailClinical implications of trigeminal nerve Recent trends in approach to nerve disorders

of maxillofacial regionReferences

Introduction to cranial nerves

• Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves which emerge from segments of the spinal cord. In humans, there are traditionally 12 pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining 10 pairs emerge from the brainstem.

THE TRIGEMINAL NERVE

Contents:• Introduction• Origin and course• Nuclei• Introduction video• Connections• Gasserian ganglion• Branches• Microscopic anatomy of nerve• Natural variants of trigeminal nerve• Parasympathetic ganglions associated with trigeminal nerve• Clinical implications of trigeminal nerve• Recent advances in approaches to disorder of trgeminal nerve

Introduction to trigeminal nerve

• largest and most complex of the 12 cranial nerves (CNs).

• supplies sensations to the face, mucous membranes, and other structures of the head.

• motor nerve for the muscles of mastication and contains proprioceptive fibers.

It exits the brain by a smaller motor root and a large sensory root coming out of the side of the pons near its upper border at its junction with the middle cerebral peduncle, the former being situated in front of and medial to the latter. The motor root unites with the sensory root of the mandibular division to form a single nerve trunk.

Nuclei of the trigeminal nerve

1. Chief sensory2. Motor 3. Mesencephalic

A cranial nerve nucleus is a collection of neurons (gray matter) in the brain stem that is associated with one or more cranial nerves. Axons carrying information to and from the cranial nerves form a synapse first at these nuclei. Lesions occurring at these nuclei can lead to effects resembling those seen by the severing of nerve(s) they are associated with. All the nuclei excepting that of the IV nerve supply nerves of the same side of the body.

http://en.wikipedia.org/wiki/Cranial_nerve_nucleus for later study on cranial nerve nucleus and its organisation

Sensory nucleus

• located in the pons• quite extensive• receives ordinary sensations from the main 3 branches of

the trigeminal nerve :ophthalmic division is in the lower part of the nucleus, and the mandibular branch is in the upper part.

• The large rostral head is the main sensory nucleus. • The caudal tapered part is the spinal tract, which is continuous with

substantia gelatinosa of Rolando in the spinal cord.

• (The apex of the posterior horn of the gray matter of the spinal cord is capped by a V-shaped or crescentic mass of translucent, gelatinous neuroglia (Glial cells), termed the substantia gelatinosa of Rolando (or SGR) (or gelatinous substance of posterior horn of spinal cord), which contains both neuroglia cells, and small nerve cells. The gelatinous appearance is due to a very low concentration of myelinated fibers.

• It is named after Luigi Rolando.)

The spinal tract is the sensory nucleus, primarily for pain and temperature.

The main sensory nucleus serves mostly for discrimination sense1,2,3,4,5

Motor nucleus:• lies ventral-medial to the sensory nucleus, near the lateral angle of

the fourth ventricle in the rostral part of the Pons• ventricular system• lateral ventricle • supply the muscles of mastication (masseter, temporalis and lateral

and medial pterygoid muscles), as well as the tensor tympani, tensor veli palatini, anterior belly of digastric and the mylohyoid muscles.

Clinical aspect:• Lesions involving motor V or the motor fibers in the trigeminal nerve

result in ATROPHY of the muscles listed above ipsilateral to the lesion. Since the pterygoids OPEN the jaw in concert with a downward and opposing inward motion, when they are weak on one side the inward vector of the opposing pterygoid is unopposed. Thus, the jaw deviates toward the WEAK SIDE (i.e., lesion side) upon opening.

Mesencephalic nucleus:

• located beneath the lateral edge of the floor of the fourth ventricle in the pons and in the lateral region of the periaqueductal grey matter in the midbrain.

• Most of the peripheral processes of mesencephalic V neurons occupy the motor root of the trigeminal nerve and are distributed to muscle spindles in the muscles of mastication.

• The central processes of mesencephalic V neurons terminate within motor nucleus V. This connection establishes the stretch reflex originating in the muscle spindles of the masticatory muscles, together with a reflex for the control of the force of the bite.

• Function : unconscious proprioception from muscle spindles-

Points to remember

a) Pain and temperature

b) 2-pt. discrimination, vibration, conscious proprioception

c) unconscious proprioception from muscle spindles

d) Motor innervation of muscles of mastication

• Spinal tract nucleus V

• Chief sensory nucleus V

• Mesencephalic nucleus V

Motor nucleus V

Introduction video :

Connections of trigeminal nerve• The main sensory nucleus

receives its afferents (as the sensory root) from the semilunar ganglion through the lateral part of the pons ventral surface. Its axons cross to the other side, ascending to the thalamic nuclei to relay in the postcentral cerebral cortex. The descending sensory fibers from the semilunar ganglion course through the pons and medulla in the spinal tract of CN V to end in the nuclei of this tract (as far as the second cervical segment).

The lateral spinothalamic tract: pathway for transmission of pain and temperature

• The proprioceptive fibers of CN V arise from the muscles of mastication and the extraocular muscles. They terminate in the mesencephalic nucleus. This nucleus has connections to the motor nucleus of CN V.

• The motor nucleus of CN V receives cortical fibers for voluntary control of the muscles of mastication.

• These fibers are mostly crossed. It also receives input from the mesencephalic and sensory nuclei.

• The axons emerge anterior to the sensory root from the lateral surface of the pons.

• This motor root joins the semilunar ganglion together with the sensory root.

The Gasserian ganglionThe semilunar (gasserian or trigeminal) ganglion is the great sensory ganglion of CN V. It contains the sensory cell bodies of the 3 branches of the trigeminal nerve (the ophthalmic, mandibular, and maxillary divisions). The ophthalmic and maxillary nerves are purely sensory. The mandibular nerve has sensory and motor functions.

• The gasserian ganglion lies in a depression on the petrous apex, within a dural fold called the Meckel cave. The sensory roots of the 3 branches of CN V are received anteriorly. They then pass from the posterior aspect of the ganglion to the pons.

• The motor root passes under the ganglion to join the sensory division of the mandibular nerve and exits the skull through foramen ovale. The carotid plexus contributes sympathetic fibers to the gasserian ganglion.

Branches of trigeminal nerveThe ophthalmic, maxillary, and mandibular branches of the trigeminal nerve leave the skull through 3 separate foramina: the superior orbital fissure, the foramen rotundum, and the foramen ovale, respectively

The Opthalmic Nerve(V1)

• First branch of the trigeminal nerve.

• Exclusively sensory• Smallest of the three

divisions• Nerve trunk is

approx. 2.5cm long

• Arises from the convex surface of the gasserian ganglion, in the dura of the lateral wall of the cavernous venous sinus under CN IV and above the maxillary nerve

• Leaves the cranium and enters the orbit through the superior orbital fissure

Sensory information from the scalp and forehead.

The eyeball, upper eyelid, the conjunctiva, cornea of the eye and

the lacrimal glands.

The nose [including the tip of the nose(external nasal nerve),

except alae nasi], the nasal mucosa.

The frontal sinuses, and parts of the meninges (the dura and

blood vessels).

Note: when the opthalmic nerve is paralaysed, the ocular

conjunctiva becomes insensitive to touch.

Coverage area

• Receives sympathetic filaments from the cavernous sinus and communicating branches from CN III and IV.

• Just before it exits the skull through the superior orbital fissure, it gives off a dural branch, and then divides into 3 branches: the frontal, lacrimal, and nasociliary

Frontal nerve-the largest branch of the ophthalmic nerve-passes in the lateral part of the superior orbital fissure, below the lacrimal nerve and above CN IV, between the periorbita and levator palpebrae superioris. -divides in the middle of the orbit into the supraorbital (larger branch) and supratrochlear nerves.

• The supraorbital nerve exits the skull through the supraorbital notch (or foramen). It supplies the upper lid and then turns superiorly under the frontalis muscle to supply the scalp (via lateral and medial branches) as far posteriorly as the lambdoid suture.

• The supratrochlear nerve exits the medial orbit and gives branches to the conjunctiva and the skin of the upper lid, as well as to the lower and medial parts of the forehead. The branch to the frontal sinus pierces it in the supraorbital notch to supply the frontal sinus mucosa.

Lacrimal nerve

Arises in the narrow, lateral part of the superior orbital fissure and courses between the lateral rectus and the periorbita.

Supplies the lacrimal gland, conjunctiva, and upper lid. In the orbit, it receives a communication from the zygomatic branch of the maxillary nerve.

This represents postganglionic parasympathetic secretory fibers from the sphenopalatine ganglion to the lacrimal gland. The preganglionic fibers reach the ganglion via the greater petrosal and vidian nerves from CN VII.

Nasociliary nerve• The nasociliary nerve travels along

the medial border of the orbital roof, giving off branches to the nasal cavity and ending in the skin at the roof of the nose.

• It then branches into the anterior ethmoidal and external nasal nerves. The internal nasal nerve (from the anterior ethmoidal ) supplies the mucous membrane of the anterior part of the nasal septum and the lateral wall of the nasal cavity.

• The ciliary ganglion contains sensory fibres that travel to the eyeball via the short ciliary nerves.

There are 2 or 3 long ciliary nerves supplying the iris and cornea.

The infratrochlear nerve supplies the skin of the lacrimal sac and the lacrimal caruncule.

The posterior ethmoidal nerve supplies the ethmoidal and sphenoidal sinuses,

The external nasal nerve supplies the skin over the apex(tip) and the ala of the nose.

Visual explanation of the opthalmic nerve

The Maxillary Nerve

• Arises from the middle of the trigeminal ganglion• Intermediate in size between the opthalmic and mandibular divisions• Purely sensory in function

Origin and courseAs it leaves the semilunar ganglion, the maxillary nerve

passes horizontally through the dura of the lateral wall of the cavernous sinus and leaves the cranial cavity through

the foramen rotundum, located in the greater wing of sphenoid

Once outside the cranium, maxillary nerve crosses the uppermost part of the pterygopalatine fossa, between pterygoid plates of the sphenoid and the palatine bone

As it crosses the fossa, it gives off :branches to the sphenopalatine ganglion, the

posterior alveolar nerve and the zygomatic branches.

It then angles laterally in a groove on the posterior surface of the maxilla, entering the orbit through the inferior orbital fissure.

Within the orbit it occupies the infraorbital groove and becomes the infraorbital nerve, which courses anteriorly into the infraorbital

canal.

The maxillary division emerges on the anterior surface of the face through the infra orbital foramen, where it divides into terminal branches, supplying the skin of the face, nose, lower eyelid, and upper lip.

Branches of the maxillary nerve

1.Within the cranium

2.In the pterygopalatine fossa

3.In the infraorbital canal

4.Branches on the face

Branch within the cranium

The maxillary division gives off a small branch, the middle meningeal nerve, which travels with the middle meningeal artery to provide sensory innervation to the duramater.

Branches in the pterygopalatine fossa

• After exiting the cranium, the V2 crosses the pterygopalatine fossa where several branches are given off:

1. The zygomatic nerve2.The pterygopalatine nerves3.The posterior superior alveolar nerve

The zygomatic nerve

Travels anteriorly, enters the orbit through the inferior orbital fissure where it divides into

1.Zygomaticotemporal nerve: supplies sensory innervation to the skin on the side of the forehead

2.Zygomaticofacial nerve: supplies the prominence of the cheek

(Note: just before leaving, the zygomatic nerve sends a branch that communicates with the lacrimal nerve of the opthalmic division. It carries secretory fibers from the sphenopalatine ganglion to the lacrimal gland)

Zygomatico temporal nerve:• The zygomaticotemporal nerve is a terminal branch of the

zygomatic nerve. It traverses a canal in the zygomatic bone to emerge into the anterior part of the temporal fossa, ascends between the bone and temporalis and finally pierces the temporal fascia 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. This lacrimal ramus conveys parasympathetic postganglionic fibres from the pterygopalatine ganglion to the lacrimal gland. UPDATE Date Added: 22 May 2006 Abstract: Surgical anatomy of the zygomaticotemporal nerve in the orbit and temporal areahttp://www.ncbi.nlm.nih.gov/pubmed/15167230?dopt=Abstract

Zygomaticofacial nerve

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

Pterygopalatine nerves

• The pterygopalatine nerves are the two trunks that unite in the pterygopalatine ganglion and then redistributed into several branches: orbital, nasal, palatal, pharyngeal.

1. The orbital branches supply the periosteum of the orbit.

2. The nasal branches : 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.

Nasopalatine nerve, a significant nerve in dentistry pass across the roof of nasal cavity downward and forward where it lies between mucous membrane of and the periosteum of the nasal septum.

It then continues downward reaching the floor of the nasal cavity and giving branches to the anterior part of the nasal septum and floor of

the nose.

It then enters the incisive canal, through which it passes into the oral cavity via the incisive foramen, located in the midline of the palate

about 1 cm posterior to the maxillary central incisors.

The right and left nasopalatine nerves emerge together through this foramen and provide sensation to the palatal mucosa in the region of

the premaxilla(canine to canine).

3. The palatine braches: include greater/anterior palatine and the lesser(middle and posterior) palatine nerves.

Greater palatine supplies sensory innervation to the palatal soft tissues and bone as far as first premolar where it communicates with terminal fibers of nasopalatine nerve.

Middle palatine nerve emerges from the lesser palatine foramen along with the posterior palatine nerve, together supplying mucous membrane of soft palate and tonsillar region respectively.

4. Pharyngeal branch is a small nerve that leaves the posterior part of the ptergopalatine ganglion, passes through the pharyngeal canal and is distributed to the mucous membrane of nasal part of the pharynx, posterior to the auditory.

Posterior superior alveolar nerve• Descends from the main trunk of the maxillary division in the

pterygopalatine fossa just before the maxillary division enters the infraorbital canal

• Commonly there are two PSA branches but on occasion a single trunk arises

• Passing down through the pterygopalatine fossa, they reach the inferior temporal(posterior) surface of maxilla

• Together, the posterior superior alveolar nerve supplies buccal gingiva in maxillary molar region, adjacent facial mucosal surfaces, mucous membrane of maxillary sinus

• Continuing downwards, the second branch of PSA provides sensory innervation to the alveoli, PDLs, and the pulpal tissues of maxillary third, second and first molars (with exception [in 28% of the patients] of the mesiobuccal root of the first molar).

Branches in the infraorbital canal

• Gives 2 significant branches within the infra orbital canal: middle superior alveolar and

anterior superior alveolarWhile in infraorbital groove and canal, the

maxillary division is known as infraorbital nerve.

Middle superior alveolar

• Branches off the main trunk within the IO canal to form a part of the superior dental plexus(reference.malamed…page 179), composed of posterior, middle and anterior superior alveolar nerves.

• Provides sensory innervation to the two maxillary premolars plus its periodontal tissues and buccal soft tissues, and perhaps to the mesio buccal root of 1st molar

Anterior superior alveolar

• Given off the infra orbital nerve approximately 6 to 10 mm before the latter’s exit from the infra orbital foramen.

• Descending within the anterior wall of maxillary sinus, provides pulpal inervation to the central and lateral incisors and the canine and sensory innervation to the periodontal tissues, buccal bone, mucous membranes of these teeth.

Organization of dental nerve supply

• Actual innervation of individual roots of all teeth, bone, and periodontal structures in max and md derives from the terminal branches of larger nerves in the region, these nerve networks are known as the DENTAL PLEXUS.

• Superior dental plexus: composed of smaller nerve fibres from the three superior alveolar nerves (and in the mandible, from the inferior alveolar nerve)

• Three types of nerves emerge from these plexuses: Dental nerve(enters a tooth through the apical foramen), Interdental branches(also c/a perforating branches- travel

through entire height of interradicular septum and provide sensory innervation to the pdl of adjacent teeth through the alveolar bone, emerge at the height of the crest to supply interdental papillae and buccal gingiva) ,

Interradicular branches(provide sensory innervation to the PDL of adjacent roots, terminate in the PDL at the root furcations).

• Each is accompanied along its pathway by a corresponding artery.

Branches on the face

• Terminal branches given by infraorbital nerve once it emerges through the IO foramen onto the face to divide into terminal branches:

Inferior palpebral: skin of lower eyelid External nasal: skin and lateral aspect of the

noseSuperior labial branches: skin and mucous

membrane of the upper lip

Visual explanation of the maxillary nerve

The Mandibular Nerve• Largest division of

the trigeminal nerve

• Mixed nerve with two roots: a larger sensory root and a smaller motor root(represents the entire motor component of the trigeminal nerve)

Origin and course• Sensory root originates at the inferior angle of the trigeminal

ganglion• Motor root arises In the motor cells located in the pons and

medulla oblongata

The two roots emerge from the cranium separately through the foramen ovale, motor root lying medial to the sensory

Unite outside the skull and form the main trunk of 3rd division

This trunk remains undivided for only 2 to 3 mm before it splits into a small anterior and large posterior divisions

Areas innervated by V3

SENSORY ROOT

•Temporal region •Auricula•External auditory meatus•Cheek•Lower lip•Lower part of face (chin region)

2.Mucous membrane

•Cheek•Tongue(anterior two thirds)•Mastoid cells

1.Skin

• 3. Mandibular teeth and pdl tissues

• 4.Bone of the mandible

• 5.Temporomandibular joint

• 6.Parotid gland

MOTOR ROOT

•masseter•Temporalis•Medial pterygoid•Lateral pterygoid

1.Muscles of mastication

•2.Mylohyoid•3.Anterior belly of digastric•4.Tensor tympani•5.Tensor veli palatini

Branches of the Mandibular Nerve

1.Branches from the undivided nerve

2.Branches from the anterior division

3.Branches from the posterior division

Branches from the undivided nerve

• On leaving the foramen ovale, main trunk gives two branches during 2-3 mm course before division:

Nervus spinosus (meningeal branch of mandibular nerve): re-enters cranium through foramen spinosum along the middle meningeal artery to supply the dura mater and the mastoid air cells

Nerve to medial pterygoid : a motor nerve to the medial/internal pterygoid muscle, gives off small branches that are motor to the tensor veli palatini and tensor tympani

Branches from the anterior division

• Provide motor innervation to the muscles of mastication and sensory innervation to the cheek and buccal mucous membrane of the mandibular molars

• Significantly smaller than the posterior

• Runs forward under the lateral/external pterygoid muscle for a short distance and then reaches the external surface of the muscle by passing between its two heads, or less frequently, winding over its upper border.

• From this point it is known as the buccal nerve

• Although under the lateral pterygoid muscle, the buccal nerve gives off several branches:

1. The deep temporal nerves ( to temporalis mucsle),

2. The masseteric nerve ( to the masseter muscle), and

3. The lateral pterygoid nerve (to the lateral pterygoid muscles)

The buccal nerve

• Also k/a the buccinator nerve or the long buccal nerve• Usually passes between the two heads of the lateral

pterygoid to reach the external surface of that muscle• Then follows the inferior part of the temporal muscle and

emerges under the anterior border of masseter, continuing in anterolateral direction

• At the level of occlusal plane of the mandibular third or second molar, it crosses in front of the anterior border of ramus and enters the cheek through the buccinator muscle

• Sensory fibres are distributed on the skin of the cheek, others passing to the retromolar triangle, providing sensory innervation to the buccal gingiva of the mandibular molars and the muccobuccal fold in that region.

Branches from the posterior division

• The posterior division of V3 is primarily sensory with a small motor component

• Descends for a short distance downward and medially to the lateral pterygoid muscle, at which point it branches into:

Auriculotemporal nerveLingual nerveInferior alveolar nerve

The auriculotemporal nerve:Traverses the upper part of the parotid gland and then

crosses the posterior portion of the zygomatic archGives off a number of branches of which all are sensory:-gives sensory, secretory and vasomotor fibers to the

parotid gland -anterior auricular branches supply the skin over helix and

tragus of ear -branches to external auditory meatus-articular branches to the posterior portion of the TMJ and -superficial temporal branches, supplying the skin over the

temporal region

The lingual nerve:2nd branch of the posterior division of V3

Passes downward medial to the lateral pterygoid muscle and, as it descends, lies between the ramus and the medial pterygoid muscle in the pterygomandibular space.

Runs anteriorly and medial to the inferior alveolar nerve whose path it parallels.

Then continues downward and forward, deep to the pterygomadibular raphe and below the attachment of the superior constrictor of the pharynx, to reach the side of base of tongue slightly below and behind the mandibular third molar, just below the mucous membrane in the lateral lingual sulcus, may even be visible in some.

• Then proceeds anteriorly across the muscles of the tongue, looping downward and medial to the wharton’s duct to the deep surface of the sublingual gland, where it breaks up into its terminal branches.

• Nature /function:Sensory to the anterior two thirds of the tongue,

providing both general and taste sensation (gustation) for this region

Also provides sensory innervation to the mucous membranes of the floor of mouth and gingiva on the lngual of the mandible.

The inferior alveolar nerve:Largest branch of the mandibular division.Descends medial to the lateral pterygoid muscle and

lateroposterior to the lingual nerve, to the region between the sphenomandibular ligament and the medial surface of ramus of mandible, where it enters the mandibular canal at the level of the mandibular foramen.

Through out its path, is accompanied by the inferior alveolar artery(branch of max. artery) and the inferior alveolar vein.

Artery lies just anterior to the nerve.The nerve, artery and vein travel anteriorly in the mandibular

canal as far forward as the mental foramen, and then terminate into terminal branches: the incisive nerve and the mental nerve.

• Note: bifid inferior alveolar nerves and mandibular canals have been observed radiographically (0.95%)

• Brings difficulty in achieving adequate anesthesia with conventional techniques

• IAN divides into two terminal branches : the incisive nerve and the mental nerve:

The incisive nerve remains within the mandibular canal and forms a nerve plexus that supplies pulpal tissues of mandibular first premolar, canine, and incisors via the dental branches.

The mental nerve exits the canal through the mental foramen and divides into three branches that innervate the skin of the chin and the skin and mucous membrane of the lower lip.

The mylohyoid nerve:Branches from the inferior alveolar nerve before the latter’s entry

into the mandibular canal.Runs downward and forward in the mylohyoid groove on the medial

surface of ramus and along the body of mandible to reach mylohyoid muscle

Is a mixed nerve: motor to the mylohyoid muscle and the anterior belly of digastric, thought to contain sensory fibers to supply skin on the inferior and anterior surface of mental protuberance

May also provide innervation to the mandibular incisorsEvidence of supply even to mandibular molars , usually the mesially

root have been found.

Microscopic anatomy

• Sensory nerve endings that respond to stimuli and convert them to nervous energy toward the central nervous system are called receptors or central transducers. Sensory receptors are classified into the following 3 main groups: exteroreceptors, interoreceptors, and proprioceptors.[6, 7, 8]

Exteroreceptors

• These are stimulated by the external environment. Examples of these types of receptors include the following:

• Merkel corpuscles - Located in submucosa of the tongue and oral cavity

• Meissner corpuscles - Tactile receptors in the skin• Ruffini corpuscles - Pressure and warmth receptors• Krause corpuscles or end bulbs - Cold receptors• Free nerve endings - Perceive superficial pain and tactile

sensations

Interoreceptors

• These are located in and transmit sensations from body cavities. Most of the sensations for these structures deal with body functions and are below the conscious level. Examples include the following:

• Pacinian corpuscles - Detect pressure sense• Free nerve endings - Perceive visceral or other

sensations

Proprioceptors

• The sensations associated with proprioceptors are also below conscious level; examples include the following:

• Muscle spindles - Respond to passive stretch of the muscle

• Golgi tendon organs - Located in tendons and respond to muscle tension (contraction and stretching)

• Pacinian corpuscles - Respond to pressure• Proprioceptors - Respond to periodontal sensation• Sensory nerve endings - Perceive deep somatic pain

Natural Variants of Trigeminal Nerve

-Different anatomic variations have been described regarding the trigeminal nerve, its branches, and its subdivisions. -Examples include the very rare occurrence of unilateral trigeminal nerve hypoplasia, in which no corneal sensitivity exists on the affected side and facial sensitivity is reduced in all branches of the trigeminal nerve. -Anomalies may coexist also in association with craniofacial anomalies, such as hypoplasia of the trigeminal nerve in Goldenhar syndrome (oculo-auriculo-vertebral dysplasia). -A few other examples affecting the different divisions are described below.[9, 10, 11, 12, 13, 14]

Frontal nerve• A variation has been reported in which the frontal nerve divides at a variable

point before leaving the orbit to form the supratrochlear and supraorbital branches. In such cases, the supraorbital branch passes through the supraorbital foramen, through which the undivided nerve ordinarily passes. When the foramen is absent, it may have a special groove, the frontal notch (Henle notch).

• The frontal nerve runs, at first forward, in a sagittal direction. In approximately 90% of subjects, it divides during its course within the orbit, but in 10% of persons it remains undivided. It divides into the larger lateral supraorbital nerve and smaller supratrochlear nerve, which runs medially.

• In 60% of subjects, the supraorbital nerve does not divide, but in 30% it divides into the medial branch, which leaves the orbit through the frontal foramen or notch, and the lateral branch passes out through the frontal foramen.

• In about 90% of subjects, the supratrochlear nerve runs along the surface of the superior oblique muscle. In 4% of subjects, 2 supratrochlear nerves exist.

• Ethmoidal nerve• This nerve may be limited to the nasal cavity. It may also traverse the

posterior ethmoidal foramen to gain entrance to the cranial cavity.• This nerve may appear to be derived from the trochlear nerve. However, the

probable source in such cases is the ophthalmic nerve, through its communicating branch to the trochlear nerve (CN IV) in the cavernous sinus.

• Lacrimal nerve• The lacrimal nerve may be small at its origin, increasing in size later in its

course by the addition of fibers derived from the temporal branch of the maxillary division of the trigeminal nerve. The lacrimal nerve may be absent and replaced by the temporal branch of the maxillary division of the trigeminal nerve.

• The lacrimal nerve occasionally gives rise to a ciliary nerve, or it receives a branch from a long ciliary nerve of the ciliary ganglion or a branch from the ganglion directly. It may receive accessory roots from the supraorbital or nasociliary nerves.

• The bifurcation of the lacrimal into its terminal branches may occur on the posterior wall of the orbital cavity. A branch of the lacrimal has been noted to pierce the sclera.

• The lacrimal nerve may exchange fibers with the ciliary ganglion.

Nasociliary (nasal) nerveSeveral variations in the branches of this nerve have been reported. The nasociliary nerve may send branches to the superior rectus, medial rectus, and levator palpebral superioris muscles. Branches emanating from a small ganglion connected to the nasal nerve have been followed to the oculomotor (CN III) and abducens (CN VI) nerves.The infratrochlear branch of the nasal (nasociliary) nerve may be missing, in which case the areas normally supplied by this branch (skin of the upper eyelid, root of nose, conjunctiva, lacrimal sac) receive their supply from the supratrochlear branch of the frontal nerve.Branches of the nasal nerve have been described passing to the frontal, ethmoid, and sphenoid sinuses. The branches to the frontal and anterior ethmoid sinuses arise in the anterior ethmoid foramen; branches to the sphenoid and posterior ethmoid sinuses arise in the posterior ethmoid foramen. The branches to the sphenoid sinuses are known as sphenoid branches, whereas the branches to the posterior ethmoid sinuses are known as sphenoethmoid or posterior ethmoid branches. An anastomosis between the nasal and lacrimal nerves has been reported.

Maxillary division (V2)The maxillary nerve may split into 2 trunks, each entering the skull through a separate foramenZygomatic nerveThe following variations have been reported in this nerve or its 2 branches (the temporal or facial or malar). The nerve may pass through the zygomatic bone before it divides into 2 branches, or the 2 branches may pass separately through foramina in the zygomatic bone instead of passing through a common foramen (sphenozygomatic foramen). The temporal branch in some cases passes through the sphenomaxillary fissure into the temporal fossa.Either branch of the zygomatic may be absent or smaller than normal, in which case the other branch compensates by carrying the additional nerve fibers. The area usually supplied by the zygomatic branch (skin of the zygomatic region) may be supplied instead by the infraorbital nerve. The area usually supplied by the temporal branch (skin of the anterior temporal region) may be supplied solely or additionally by the lacrimal nerve.

Posterior superior alveolar nerveIn the absence of the buccal nerve, the posterior superior alveolar nerve distributes branches to the areas normally supplied by this nerve (mucous membrane and skin of the cheek).Inferior alveolar nerveThe inferior alveolar nerve may form a single trunk with the lingual nerve, extending as far as the mandibular foramen. The inferior alveolar nerve is sometimes perforated by the internal (medial) maxillary artery. It may have accessory roots from other divisions of the mandibular nerve. In some cases, the mylohyoid branch of the inferior alveolar gives rise to a branch that pierces the mylohyoid muscle and joins the lingual nerve.Branches have been described arising from the mylohyoid branch and supplying the depressor anguli oris muscle and parts of the platysma (that are usually supplied by the facial nerve), the skin below the chin, and the submandibular (submaxillary) gland (which is usually supplied by the facial nerve). The inferior alveolar may form connections with the auriculotemporal nerve. In one case, the roots of the third lower molar tooth were found to be surrounding the inferior alveolar nerve.

Auriculotemporal nerveThis nerve carries the otic ganglion, which is derived from glossopharyngeal neurons. The nerve usually arises by 2 roots from the posterior division of the mandibular nerve. The 2 roots usually surround the middle meningeal nerve before joining to form a single trunk. A variation in this relationship has been described in which the middle meningeal artery pierces the anterior root instead of passing between the 2 roots.According to Baumel et al, the auriculotemporal nerve is commonly misrepresented in illustrations and textbooks.[11] Their 85 dissections of the nerve demonstrated that the roots of the "typical" auriculotemporal nerve do not form a tight buttonhole around the middle meningeal artery. Instead, the roots outline an elongated, V-shaped interval, with the roots widely separated from one another. At their junction, the roots form a short trunk that immediately breaks up in line with the posterior border of the mandible into a spray of branches.The superficial temporal ramus of the auriculotemporal nerve should not be considered as the main continuation of the nerve but merely as its largest branch. A substantial portion of the nerve makes up its 2 communicating rami with the facial nerve; these are the strongest and most consistent of the many peripheral communications between trigeminal and facial nerves. Common variations in configuration, branching, and relationships of the nerve are discussed in the report by Baumel et al.

Lingual nerveA minute sublingual ganglion has been described arising from the lingual nerve or submandibular ganglion (a ganglion of the facial nerve carried by the lingual nerve), supplying the sublingual gland. This nerve may pierce the lateral pterygoid muscle rather than pass between the 2 pterygoid muscles. It occasionally provides motor branches to the medial and lateral pterygoids and to the palatoglossus muscle.

Pathophyscial variants

• http://emedicine.medscape.com/article/1873373-overview#aw2aab6b6

• (To be discussed in section of trigeminal nerve disorders)

Parasympathetic Ganglia

Four small parasympathetic (accessory) ganglia are associated anatomically (but not functionally) with the branches of the trigeminal nerve.[2, 4] They are as follows:

• Ciliary ganglion• Sphenopalatine (or pterygopalatine) ganglion• Otic ganglion• Submandibular ganglion

The ciliary ganglionThe ciliary ganglion is associated with the ophthalmic

nerve. It is the size of a pinhead and has the following 3 roots:

• The parasympathetic root from the nerve to inferior oblique (CN III) from Edinger Westphal nucleus and caudal central nucleus to supply the sphincter papillae and ciliary muscles

• Sympathetic root from the nasociliary nerve to dilator papillae muscle of the eye

• Sensory root from the nasociliary nerve to the cornea

Spheno-palatine ganglion

• The sphenopalatine ganglion is associated with the maxillary nerve. It receives its parasympathetic fibers from CN VII (as seen in the image below). The otic and submandibular ganglia are associated with the mandibular nerve. They receive parasympathetic fibers from CNs IX and VII, respectively.

Clinical implications of trigeminal nerve

• Damage to the complete nerve leads to the following features on affected side– Unilateral anesthesia of the face– Unilateral anesthesia on the anterior aspect of the scalp– Unilateral anesthesia on the auricle– Unilateral anesthesia of the mucous membrane of mouth– Unilateral anesthesia of the mucous membrane of nose– Unilateral anesthesia of the anterior 2/3 of the tongue– Unilateral paralysis of muscles of mastication

• Trigeminal neuralgia affects one or more of the divisions of the trigeminal nerve causing severe pain

• Carcinoma of the tongue which affects the lingual nerve may refer pain to the distribution of the auriculotemporal nerve, causing ear ache.

Recent trends in approach to nerve disorders of maxillofacial region

1.The fine branches of the human trigeminal nerve.

• Uryvaev MY, Sudarikova TV, Trufanov IN, Gorskaya TV, Tsybul'kin AG.• Source• Department of Human Anatomy, Moscow State Medical-Stomatological University, Russia.• Abstract• The fine branches of the trigeminal ganglion were studied by macro micropreparation and

total clearing in glycerol of specimens collected during autopsies of 78 people aged 23-69 years impregnated with silver nitrate by the Christensen method or stained with the Schiff reagent as described by Shubich and Khodos; serial histotopograms prepared in the sagittal plane from specimens from 15 autopsies of humans of the same age range and also impregnated by the Christensen method were also studied. Four histotopograms were used for reconstruction of the fine nerves. The results showed that numerous branches of diameter 50-150 microm ran directly from the trigeminal nerve, more from the outer and less from the deeper surface, innervating the walls of the trigeminal cavity. No connecting branches of the trigeminal ganglion to the internal carotid plexus, greater petrous nerve, or any other nerve were seen.

• http://www.ncbi.nlm.nih.gov/pubmed/18197382%2C18197383?dopt=Abstract

2.Imaging the trigeminal nerve.• Borges A, Casselman J.• Source• Radiology Department, Instituto Português de Oncologia Francisco Gentil, Centro de Lisboa, Rua Prof. Lima Basto,

1093, Lisboa, Portugal. borgalexandra@gmail.com• Abstract• Of all cranial nerves, the trigeminal nerve is the largest and the most widely distributed in the supra-hyoid neck. It

provides sensory input from the face and motor innervation to the muscles of mastication. In order to adequately image the full course of the trigeminal nerve and its main branches a detailed knowledge of neuroanatomy and imaging technique is required. Although the main trunk of the trigeminal nerve is consistently seen on conventional brain studies, high-resolution tailored imaging is mandatory to depict smaller nerve branches and subtle pathologic processes. Increasing developments in imaging technique made possible isotropic sub-milimetric images and curved reconstructions of cranial nerves and their branches and led to an increasing recognition of symptomatic trigeminal neuropathies. Whereas MRI has a higher diagnostic yield in patients with trigeminal neuropathy, CT is still required to demonstrate the bony anatomy of the skull base and is the modality of choice in the context of traumatic injury to the nerve. Imaging of the trigeminal nerve is particularly cumbersome as its long course from the brainstem nuclei to the peripheral branches and its rich anastomotic network impede, in most cases, a topographic approach. Therefore, except in cases of classic trigeminal neuralgia, in which imaging studies can be tailored to the root entry zone, the full course of the trigeminal nerve has to be imaged. This article provides an update in the most recent advances on MR imaging technique and a segmental imaging approach to the most common pathologic processes affecting the trigeminal nerve.

• Copyright (c) 2010 Elsevier Ireland Ltd. All rights reserved.• PMID: 20227216 [PubMed - indexed for MEDLINE]• http://www.ncbi.nlm.nih.gov/pubmed/20227216%2C20227217?dopt=Abstract

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