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TRIGEMINAL NERVES

Anatomy

by Dr. Nadira. A

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The trigeminal nerve is the largest cranial

nerve and contains both sensory and motor

fibres.

They are the chief sensory nerves for the

face and head, receiving impulses of pain,

temperature and touch.

The motors fibres stimulate the muscles ofmastication.

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TRIGEMINAL NERVE NUCLEI

There are four trigeminal nuclei: one motor andthree sensory

The motor nucleus of CNV is in the superior part ofthe pons, deep to the floor of the 4th ventricle.

The mesencephalic nucleus of CNV is lateral tothe cerebral aqueduct.

The principal sensory nucleus is in the dorsolateralarea of the pontine tegmentum at the level of entryof the sensory fibres.

The spinal nucleus of CNV is in the inferior part ofthe pons and throughout the medulla

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SENSORY COMPONENTS OF

TRIGEMINAL NERVE The sensations of pain, temperature, touch andpressure from the skin of the face and mucous

membrane travel along axons whose cell bodies are

situated in the semilunar or trigeminal sensoryganglion.

The central process of these cells form the large

sensory root of the trigeminal nerve.

About half the fibres divide into ascending anddescending branches when they enter the pons, the

remainder ascend or descend without division

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The ascending branches terminate in the mainsensory nucleus and the descending branchesterminate in the spinal nucleus.

The sensations of touch and pressure are conveyed

by nerve fibres that terminate in the main sensorynucleus. The sensation of pain and temperaturepass to the spinal nucleus.

The sensory fibres from the ophthalmic division ofthe trigeminal nerve terminate in the inferior part of

the spinal nucleus, fibres from the maxillary divisionterminate in the middle of the spinal nucleus andfibres from the mandibular division end in thesuperior part of the spinal nucleus.

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Propioceptive impulses from the muscles ofmastication and from the facial and extraoccularmuscles are carried by fibres in the sensory root ofthe trigeminal nerve.

The axons of the neurons in the main sensory andspinal nuclei now cross the median plane andascend as the trigeminal lemniscus to terminate onthe nerve cells of the ventral posteromedial nucleusof the thalamus.

The axons of these cells travel through the internalcapsule to the postcentral gyrus ( area 3, 2 and 1 )of the cerebral cortex.

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Motor component of the trigeminal

nerve The motor nucleus receives corticonuclearfibres from both cerebral hemispheres.

It also receives fibres from the reticular

formation , the red nucleus, the tectum, andthe medial longitudinal fasciculus.

It also receives fibres from the

mesencephalic nucleus to form amonosynaptic reflex arc.

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The cells of the motor nucleus give rise to the

axons that form the motor root.

The motor nucleus supplies the muscles of

mastication, the tensor tympani, the tensorveli palatini, the myelohyoid and the anterior

belly of the digastric muscle.

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COURSE OF THE TRIGEMINAL

NERVE The trigeminal nerve leaves the anterior aspect of the pons as asmall motor root and a large sensory root.

The nerve passes forward out of the posterior cranial fossa andrests on the upper surface of the apex of the petrous part of thetemporal bone in the middle cranial fossa.

The large sensory root now expands to form the cresent shapedtrigeminal ganglion, which lies within a pouch of dura matercalled the trigeminal or Meckels cave.

The ophthalmic, maxillary and the mandibular nerves arisesfrom the anterior border of the ganglion.

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The ophthalmic nerve contains only sensoryfibres and leaves the skull through thesuperior orbital fissure to enter the orbital

cavity. The maxillary nerve also contains only

sensory fibres and leaves the skull throughforamen rotundum.

The mandibular nerve contains both sensoryand motor fibers and leaves the skull throughthe foramen ovale.

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Divisions and branches of

trigeminal nerve There are three main branches of thetrigeminal nerves.

Ophthalmic nerve sensory only

Maxillary nerve sensory only

Mandibular nerve sensory and motor

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Ophthalmic nerve

A sensory nerve passes through the superior

orbital fissure and supplies the eyeball,

conjunctiva, lachrymal gland and sac, nasal

mucosa, frontal sinus, frontal sinus, externalnose, upper eyelid, forehead and scalp.

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Branches

Tentorial nerve Lachrymal nerve Frontal nerve supraorbital nerve - supratrochlear nerve Nasociliary nerve Short ciliary nerves

Long ciliary nerves Infratrochlear nerve Anterior and posterior ethmoidal nerves.

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Maxillary nerve

A sensory nerve passes through the foramen rotundum. It

suppliesthe cheeks, upper gums, upper teeth and lower eyelids.

Branches

Meningeal branch Zygomatic nerve Posterior superior alveolar branches Infraorbital nerve Greater palatine nerves Lesses palatine nerve Lesser palatine nerves Posterior superior lateral nasal branches Nasopalatine nerve

Pharyngeal nerve19www.similima.com

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Mandibular nerve

Largest of the three divisions and has amotor nerve and sensory nerve. It passesthrough the foramen ovale.

Meningeal branch Buccal nerve General sensory nerves

Auriculotemporal nerve Lingual nerve Inferior alveolar nerve

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Branchial branches to muscles

Masseter

Temporal

Medial and lateral pterygoids

Tensor veli palatine

Mylohyoid Anterior belly of digastric

Tensor tympani

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Trigeminal nerve injury

The nerve may be injured by trauma,tumours, aneurysms, or meningeal infection.Occasionally it may be involved in

poliomyelitis and generalized polyneuropathy,a disease involving several nerves. Thesensory and motor nuclei in the pons andmedulla may be destroyed by intramedullary

tumours or vascular lesions. An isolatedlesion of the spinal trigeminal tract also mayoccur with multiple sclerosis.

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Injury to the CN V causes; Paralysis of the muscles of mastication with

deviation of the mandible (lower jaw) toward theside of lesion.

Loss of inability to appreciate soft tactile, thermal, orpainful sensations in the face.

Loss of corneal reflex and the sneezing reflex. Common causes of facial numbness are dental

trauma, herpes zoster, cranial trauma, head andneck tumours, intracranial tumours, and idiopathictrigeminal neuropathy.

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Trigeminal neuralgia

Trigeminal neuralgia or tic douloureux is theprincipal disease affecting the sensory root ofCN V. It is characterized by attacks of

excruciating pain in the area of distribution ofthe maxillary or mandibular divisions or both.The maxillary nerve is most frequentlyinvolved. The paroxysms of excruciating pain

in the area of its distribution are often set offby touching the most sensitive area. Usuallythe cause of the neuralgia is undetectable.

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Thank you

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