Introduction to The Trigeminal Nerve

What are cranial nerves?

• Cranial nerves are nerves that emerge directly

from the brain

• There are 12 pairs of cranial nerves

• Only the first 2 originate from the cerebrum,

the others originate from the brain stem

• Trigeminal nerve is the FIFTH cranial nerve

The cranial nerves• Ⅰ Olfactory nerve • Ⅱ Optic nerve • Ⅲ Oculomotor nerve • Ⅳ Trochlear nerve

• Ⅴ Trigeminal nerve • Ⅵ Abducent nerve • Ⅶ Facial nerve • Ⅷ Acoustic nerve • Ⅸ Glossopharyngeal nerve• Ⅹ Vagus nerve • Ⅺ Accessory nerve • Ⅻ Hypoglossal nerve

Classification of cranial nerves• Sensory cranial nerves:

– contain only afferent (sensory) fibers

• Motor cranial nerves:

– contain only efferent (motor) fibers

• Mixed nerves:

– contain both sensory and motor fibers

TRIGEMINAL NERVE

Trigeminal nerve

• 5th cranial nerve (CN5)

• Largest cranial nerve

• MIXED CRANIAL NERVE

• Sensory to face – 3 dermatomes

• Motor to muscles of mastication

View of brain from below showing trigeminal ganglion and trigeminal nerves

Nuclei

• Sensory nuclei – largest cranial nerve nuclei• Sensory nuclei –mid-brain, pons and medulla• Sensory nuclei – 3 parts– Mesencephalic nucleus– Primary/Main sensory (pontine) nucleus– Spinal trigeminal nucleus

• Motor nucleus – mid-pons

Trigeminal ganglion(semilunar/gasserian /gasser’s ganglion)

• Semilunar in shape • Situated in Meckel’s cavity /cave on ‘Trigeminal

depression’ present on petrous temporal bone• Contains the cell bodies of incoming sensory

nerve fibers• Convex surface below to which the 3 nerve roots

converge: – Opthalmic division– Maxillary division– Mandibular division

Trigeminal ganglion - shape

5

Semi lunar

Ganglion

3 2

1

Motor root

Superior orbital fissure

Foramen rotundumForamen

ovale

To sensory nuclei

To muscles of mastication/ swallowing

Trigeminal dermatomes

• Areas of cutaneous sensory innervation• Show very little overlap• Injection of local anesthesia shows loss of

sensation from very well defined areas• Knowledge of dermatomes helps in– Locating site of nerve injury– Testing result of nerve block

V1- OPTHALMIC DIVISION

V2 – MAXILLARY DIVISION

V3 – MANDIBULAR DIVISION

Applied anatomy• Knowledge of dermatomes and their nerve

supply helps locate site of nerve injury• Also helps in demonstrating effect of nerve

block• Intracranial causes of trigeminal neuralgia• Pain control and modulation

Stimulus – pin prick

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