The trigeminal nerve V
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The trigeminal nerve V
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As the name suggests, this nerve
consists of three divisions. Together they supply sensory fibres to the greater
part of the skin of the head and face, the mucous membranes of the mouth, nose
and paranasal air sinuses and, by way of a small motor root, the muscles of
mastication.
The trigeminal ganglion:
This ganglion, which is also termed the semilunar ganglion, is equivalent to the dorsal
sensory ganglion of a spinal nerve. It is crescent-shaped and is situated
within an invaginated pocket of dura in the middle cranial fossa. It lies near
the apex of the petrous temporal bone, which is somewhat hollowed for it. The
motor root of the trigeminal nerve and the greater superficial petrosal nerve
both pass deep to the ganglion. Above lies the hippocampal gyrus of the
temporal lobe of the cerebrum; medially lies the internal carotid artery and
the posterior part of the cavernous sinus. The trigeminal ganglion represents
the 1st cell station for all sensory fibres of the trigeminal nerve except
those subserving proprioception.
1- The ophthalmic division:
This is the smallest division of the
trigeminal nerve; it is wholly sensory and is responsible for the innervation
of the skin of the forehead, the upper eyelid, cornea and most of the nose.
Passing forwards from the trigeminal ganglion, it immediately enters the
lateral wall of the cavernous sinus where it lies beneath the trochlear nerve Just
before entering the orbit it divides into three branches, frontal, lacrimal and
nasociliary. The frontal nerve runs forward just beneath the roof of the orbit for a short
distance before dividing into its two terminal branches, the supratrochlear and supra-orbital nerves, which supply the upper
eyelid and the scalp as far back as the lambdoid suture.
The lacrimal nerve supplies the lacrimal gland
(with postganglionic
parasympathetic fibres from
the pterygopalatine ganglion which reach it
by way of the maxillary nerve)
and the lateral part of the conjunctiva and
upper lid.
The nasociliary nerve gives branches to the ciliary
ganglion, the eyeball,
cornea and conjunctiva the
medial half of the upper eyelid, the dura of the
anterior cranial fossa, and to
the mucosa and skin of the nose.
2: The maxillary nerve
The maxillary nerve is again purely
sensory. Passing forwards from the
central part of the trigeminal
ganglion, close to the cavernous sinus, it
leaves the skull by way of the
foramen rotundum and emerges into the upper part
of the pterygopalatine fossa. Here it gives off a number of branches before
continuing through the inferior orbital fissure and the infra-orbital canal as
the infra-orbital nerve which supplies the skin
of the cheek and lower eyelid. The maxillary nerve has the following named
branches:
1◊◊the zygomatic nerve, whose zygomaticotemporal and zygomaticofacial branches supply
the skin of the temple and cheek respectively;
2◊◊superior alveolar (dental) branches to the teeth of the upper jaw; and
3◊◊the branches from the pterygopalatine ganglion, which run a descending course and are distributed as follows: the greater and lesser palatine nerves, which pass through the
corresponding palatine foramina to supply the mucous membrane of the hard and
soft palates, the uvula and the tonsils, and the mucous membrane of the nose
and a pharyngeal
branch supplying
the mucosa of the nasopharynx. The nasopalatine nerve (long sphenopalatine) supplies the nasal septum then emerges
through the incisive canal of the hard palate to supply the gum behind the
incisor teeth. The posterior superior lateral nasal nerves (short sphenopalatine) supply the posterosuperior
lateral wall of the nose.
3: The mandibular nerve
This is the largest of the three divisions
of the trigeminal nerve and the onlyone to convey motor fibres. In addition to supplying the skin of
the temporal region, part of the auricle and the lower face, the mucous
membrane of the anterior two-thirds of the tongue and the floor of the mouth,
it also conveys the motor root to the muscles of mastication and secretomotor fibres
to the salivary glands. Passing forwards from the trigeminal ganglion, it
almost immediately enters the foramen ovale through which it reaches the
infratemporal fossa. Here it divides into a small anterior and a larger
posterior trunk, but before doing so it gives off the nervus spinosus to supply the dura mater and
the nerve to the medial pterygoid
muscle from
which the otic
ganglion is
suspended and through which motor fibres are transmitted to tensor palati and
tensor tympani.
The anterior trunk gives off:
1◊◊a sensory branch, the buccal nerve, which supplies part of the skin of the cheek and the mucous
membrane on its inner aspect; and
2◊◊motor branches to the masseter, temporalis and lateral pterygoid
muscles.
The posterior trunk, which is principally sensory, divides into three branches:
The posterior trunk, which is principally sensory, divides into three branches:
a- the auriculotemporal nerve, which conveys sensory fibres
to the skin of the temple and auricle and secretomotor fibres from the otic
ganglion to the parotid gland;
b- the lingual nerve, which passes downwards under
cover of the ramus of the mandible to the side of the tongue , where
it supplies the mucous membrane of the floor of the mouth, the anterior
two-thirds of the tongue (including the taste buds by way of fibres which join
it from the chorda tympani), and the sublingual and submandibular salivary
glands;
c- the inferior alveolar (dental) nerve, which passes down into the
mandibular canal and supplies branches to the teeth of the lower jaw. It then
emerges from the mental foramen to supply the skin of the chin and lower lip.
This branch also conveys the only motor component of the posterior trunk: the nerve to the mylohyoid, supplying the muscle of that
name and the anterior belly of the digastric.
Common Disorders of the Trigeminal Nerve –
Clinical features
1◊◊Section of the whole trigeminal nerve results in unilateral
anaesthesia of the face and anterior part of the scalp, the auricle and the
mucous membranes of the nose, mouth and anterior two-thirds of the tongue,
together with paralysis and wasting of the muscles of mastication on the
affected side. Lesions of separate divisions give rise to corresponding sensory
and motor deficits in the area of distribution of the affected nerve.
2◊◊Trigeminal neuralgia may affect any one or more of the three
divisions, giving rise to the characteristic pain over the appropriate area
3◊◊Pain is frequently referred from one segment to another. Thus, a
patient with a carcinoma of the tongue (lingual nerve) frequently complains
bitterly of earache (auriculotemporal nerve). The classical description of such
a case is an old gentleman sitting in out-patients spitting blood and with apiece of cotton wool in his
ear.
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