Nerve Supply Lecture Notes

Nerve Supply Overview

  • Focus on cranial nerves 5, 7, 9, 10, cervical plexus, and sympathetic trunk.

Trigeminal Nerve (Cranial Nerve V)

General Information

  • Main sensory nerve of the head.

  • Motor nerve for muscles of mastication.

  • Emerges from the anterior surface of the pons with a large sensory root and a small motor root.

  • Passes out of the posterior cranial fossa, carrying the trigeminal cave.

  • Expands at the petrous temporal bone, forming the gasserian (trigeminal) ganglion within the trigeminal cave.

Divisions of Trigeminal Nerve

  1. Ophthalmic Division

    • Purely sensory (smallest division).

    • Exits the skull via the superior orbital fissure.

    • Lies in the lateral wall of the cavernous sinus.

    • Branches include:

      • Frontal Branch:

      • Splits into supratrochlear and supraorbital nerves (supply forehead).

      • Lacrimal Nerve:

      • Supplies the lacrimal gland.

      • Naso-Ciliary Nerve:

      • Forms ciliary ganglion and gives off branches:

        • Internal nasal branches, posterior ethmoidal nerve, long ciliary nerve, external nasal nerve (supply areas of the nose).

  2. Maxillary Division

    • Also purely sensory.

    • Exits the skull at the foramen rotundum.

    • Enters the orbit via the inferior orbital fissure, becoming the infraorbital nerve.

    • Branches include:

      • Ganglionic Branches:

      • Send nerve fibers to the pterygopalatine ganglion.

      • Infraorbital Nerve:

      • Supplies the ala of the nose.

      • Superior Alveolar Nerves: (Posterior, Middle, Anterior Superior):

      • Supply upper teeth.

      • Zygomatic Nerve:

      • Supplies the lateral cheek and temple; splits into:

        • Zygomatico-Facial Nerve and Zygomatico-Temporal Nerve (the latter sends parasympathetic fibers to the lacrimal gland).

  3. Mandibular Division

    • Largest and mixed (sensory and motor).

    • Exits skull through the foramen ovale.

    • Branches include:

      • Direct Branches:

      • Meningeal branch, auriculotemporal, buccal, mental nerves.

      • Anterior Branch:

      • Motor nerves to masseter, temporalis, medial and lateral pterygoid muscles (muscles of mastication).

      • Posterior Division:

      • Mainly sensory; branches include:

        • Lingual Nerve:

        • Supplies general sensation to the anterior two thirds of the tongue; joins chorda tympani from cranial nerve 7.

        • Inferior Alveolar Nerve:

        • Forms inferior dental plexus, supplies skin and mucous membrane of the lower lip, chin, and gingiva of mandibular incisor teeth.

        • Motor Nerves to Mylohyoid and Digastric Muscles.

Clinical Correlation: Trigeminal Neuralgia

  • Known as "stick doleru", involves severe pain along one or more divisions, typically maxillary.

  • Pain triggers can be light stimuli (e.g., wind).

  • Treatment options may include surgical decompression and medication.

Clinical Correlation: Bell's Palsy

  • Temporary weakness or paralysis of facial muscles due to facial nerve inflammation.

  • Affected side of the face droops; difficulty smiling or closing eyes.

Facial Nerve (Cranial Nerve VII)

General Information

  • Leaves the skull and gives off nerves to posterior belly of digastric and stylohyoid muscles.

  • Terminal branches within the parotid gland include:

    • Posterior Auricular Nerve.

    • Five branches: Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical.

Mnemonics for Facial Branches

  • Mnemonic: "The zookeeper brought the male monkey, carrots, and papaya."

    • Temporal Branch:

    • Supplies auricularis superior, anterior frontal belly of occipito-frontalis, superior parts of orbicularis oculi.

    • Zygomatic Branch:

    • Innervates inferior part of orbicularis oculi and facial muscles inferior to the orbit.

    • Buccal Branch:

    • Innervates buccinator, upper lip, and upper parts of orbicularis oris.

    • Marginal Mandibular Branch:

    • Innervates muscles of lower lip and chin.

    • Cervical Branch:

    • Innervates platysma.

Functional Components of Facial Nerve

  • Medial Motor Root:

    • Carries efferent fibers to muscles of facial expression.

    • Innervates stapedius, stylohyoid, and posterior belly of digastric.

  • Lateral Sensory Root (Nervous Intermedius):

    • Emerges between the motor root and vestibular nerve.

    • Carries SPA fibers for taste from anterior two-thirds of the tongue and soft palate via chorda tympani.

    • Carries preganglionic parasympathetic fibers to pterygopalatine ganglion and submandibular ganglia.

Clinical Correlation: Bell's Palsy

  • Involves lower motor neuron disease affecting the facial nerve leading to facial paralysis.

  • Symptoms depend on the location of nerve injury:

    • At the Parotid Gland: Ipsilateral facial paralysis.

    • At Facial Canal: Previous symptoms plus loss of taste and salivation.

    • At Geniculate Ganglion: All previous symptoms plus ear pain.

    • At Internal Auditory Meatus: Symptoms of all previous sites & vestibulocochlear nerve involvement.

Glossopharyngeal Nerve (Cranial Nerve IX)

General Information

  • Mixed nerve originating from the medulla; exits the skull via the jugular foramen with cranial nerves X and XI.

  • Contains two sensory ganglia:

    • Superior Ganglia: Provides visceral sensation.

    • Inferior Ganglia: Gives taste and sensation to the external ear.

Branches of Glossopharyngeal Nerve

  • Lingual Branch: Supplies general sensation and taste to the posterior one-third of the tongue.

  • Pharyngeal Branch: Supplies visceral sensation to tonsils and pharynx; motor fibers to stylopharyngeus muscle.

  • Tympanic Branch: Provides sensation and parasympathetic fibers to the parotid gland and sensory innervation to the external ear.

  • Carotid Branch: Supplies sensation to the carotid body and sinus.

Vagus Nerve (Cranial Nerve X)

General Information

  • Mixed nerve with 8-10 rootlets originating in the medulla; exits the skull through the jugular foramen.

  • Contains two sensory ganglia:

    • Superior Vagal Ganglion: Within the jugular foramen.

    • Inferior Vagal Ganglion: Below the jugular foramen.

  • Supplies the heart, digestive tract, and respiratory system.

Clinical Correlation

  • Post neck dissection patients may exhibit voice changes due to potential stretching or damage to the vagus nerve, affecting laryngeal innervation.