Trigeminal NerveNotesMed.com

Trigeminal Nerve• Largest cranial

nerve.

• Contains both sensory and motor fibers.

• It is the sensory to the greater part of the head and motor to mainly the muscles of mastication.

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Functional componentGeneral somatic afferent (GSA):-• Carry general sensations from the skin of face and scalp,

teeth, gum, oral and nasal cavities with paranasalsinuses, cornea, conjunctiva and most of the duramater.

• The cell bodies of neurons for general sensations are located in the trigeminal ganglion.

• Carry proprioceptive sensation from the muscles of mastication & extraocular muscles.

• The cell bodies are located in the mescencephalicnucleus of the 5th nerves.

Special visceral efferent (SVE):-• Conveyed by the motor root to supply the muscles which

are developed from the first branchial arch- muscles of mastication, tensor tympani and tensor velli palatini, mylohyoid and ant. Belly of digastric muscle.

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Nuclei

• Sensory nucleus (main)

• Spinal nucleus

• Mesencephalic nucleus

• Motor nucleus

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Sensory nucleus and its communication

• Main sensory nucleus:– Lies in the posterior part

of the pons and continuous below with spinal nucleus

– It receives fibres from trigeminal ganglion by sensory roots (sensation of touch and pressure)

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• Extends from the caudal end of the main sensory nucleus to the 2nd or 3rd

cervical segments of spinal cord.

• It receives the pain and temperature sensation from all trigeminal areas via sensory root.

Spinal nucleus

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Mescencephalic nucleus • Lateral part of the

grey matter around the cerebral aqueduct.

• Contains cell bodies of the unipolar first sensory neurons for the proprioceptiveimpulses from the muscles of mastication, face and extra ocular muscle.

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Sensory component of trigeminal nerve

• Sensations of pain, temperature, touch, and pressure from the skin of the face and mucous membranes travel along axons whose cell bodies are situated in the semilunar or trigeminal sensory ganglion

• Central processes of these cells form the large sensory root of the trigeminal nerve

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• About half the fibers divide into ascending and descending branches when they enter the pons

• The remainder ascend or descend without division

• The ascending branches terminate in the main sensory nucleus, and the descending branches terminate in the spinal nucleus

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• Proprioceptiveimpulses from the muscles of mastication and from the facial and extraocularmuscles are carried by fibers in the sensory root of the trigeminal nerve that have bypassed the semilunar or trigeminal ganglion

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Motor nucleus and its communication• In the pons medial to the

main sensory nucleus.• Receives corticonuclear

fibres from both cerebral hemispheres.

• Also receives from the reticular formation, red nucleus, tectum and medial longitudinal fasciculus.

• Supplies the muscles of mastication, tensor tympani, tensor velipalatini, mylohyoid and ant. belly of digastricmuscle.

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Course of the trigeminal nerve

• Leaves the anterior aspect of the pons

• Passes forward out of the post. Cranial fossa

• Rests on the upper surface of the apex of the petrous part of the temporal bone in the middle cranial fossa.

• Sensory root expands to form the crescent shaped trigeminal ganglion- lies within a pouch of duramater-trigeminal or Meckel’scave.

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Trigeminal Nerve• 3 divisions of the nerve arises from the anterior border of the

ganglion.– Ophthalmic division– leaves the skull through superior orbital fissure.– Maxillary division– foramen rotundum.– Mandibular division– foramen ovale.

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Branches and distribution

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• Ophthalmic division- tip and side of nose, upper eyelid and forehead.

• Maxillary division- upper lip, side and ala of nose, lower eyelid, upper part of cheek and small portion of temple

• Mandibular division- lower lip, chin, skin overlying the mandible except its angle, cheek, part of the pinna and external acoustic meatus and most of the temple.

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Ophthalmic nerve• Frontal nerve– largest branch and divide into

supratrochlear and supraorbital nerve.• Nasociliary nerve –1. Communicating branch to the ciliary ganglion 2. Long ciliary nerves– supply sensory nerves to cornea,

iris and ciliary body3. Posterior ethmoidal nerve – ethmoidal and sphenoidal

air sinuses 4. Infratrochlear nerve – conjunctiva, lacrimal sac, medial

end of eyelid and upper half of external nose 5. Anterior ethmoidal nerve –supply the lower half of

nose.

• Lacrimal nerve – supplies lacrimal gland

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Maxillary nerve• In the cranial cavity – meningeal branch• In the pterygopalatine fossa – ganglionic, zygomatic , post

superior alveolar nerve• In the infraorbital canal – middle and anterior sup alveolar

nerve• On the face – palpebral, nasal and superior labial nerve

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Mandibular nerve• From main trunk – meningeal branch and nerve to the medial

pterygoid• From anterior trunk – buccal nerve (sensory), masseteric, deep

temporal and nerve to the lateral pterygoid• From posterior trunk– auriculotemporal, lingual and inferior

alveolar nerve

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Applied anatomy• Sensory function tested

by using cotton and a pin over each area of the face. In lesions of ophthalmic div. cornea and conjunctiva will be insensitive to touch.

• Motor function tested by asking the patient to clench the teeth.

• Trigeminal neuralgia-severe and stabbing pain over the face.

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Trigeminal neuralgia (tic douloureux):

• It is a clinical condition which presents as a paroxysmal episodes of severe pain of sudden onset and short duration in the area of distribution of one or more of the three divisions of the trigeminal nerve.

• The ophthalmic division (CN V1) is not commonly involved. The most commonly trigeminal neuralgia is associated with maxillary (CN V2) and mandibular divisions (CN V3) of the trigeminal nerve. It is often associated with dental caries.

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