Lecture Notes: Trigeminal Nerve (Cranial Nerve 5)

Overview

• The trigeminal nerve (Cranial Nerve 5) is crucial for facial sensation (touch, pain, temperature) and mastication (chewing).
• Topics Covered:
  • Origin and path of the nerve
  • Different branches
  • Structures supplied by the nerve
  • Clinical correlation: Trigeminal neuralgia

Origin of the Nerve

• Trigeminal Ganglion: Group of cell bodies in the PNS.
• Branches:
  • V1: Ophthalmic Division
  • V2: Maxillary Division
  • V3: Mandibular Division
• Central Processes: Extend to the brainstem; connect to various nuclei:
  • Spinal Nucleus (Medulla): Controls touch, pain, temperature, pressure, and proprioception of the face.
  • Principal Pontine Nucleus (Pons): Picks up touch and proprioception, especially of the jaw.
  • Mesencephalic Nucleus (Midbrain): Specifically for proprioception of the face.

Path of V1 (Ophthalmic Division)

• Location: Lateral wall of the cavernous sinus; exits via the superior orbital fissure.
• Branches:
  • Lacrimal Branch: Supplies the lacrimal gland, superior eyelid skin, and conjunctiva.
  • Frontal Branch: Divides into the supra-trochlear (supplies skin of forehead/ upper eyelid) and supra-orbital nerves (supplies skin up to vertex of the skull).
  • Nasociliary Branch: Breaks into short ciliary and long ciliary nerves; supplies cornea, ciliary body, and iris.
  • Anterior Ethmoidal Nerve: Supplies anterior ethmoid sinus, nasal cavity, medial and lateral nasal regions, and tip of the nose.
  • Infratrochlear Nerve: Supplies medial eyelid, lacrimal sac, and caruncle.

Path of V2 (Maxillary Division)

• Location: Passes through the foramen rotundum into the pterygopalatine fossa.
• Branches:
  • Meningeal Branch: Supplies dura mater.
  • Zygomatic Branches: Zygomaticotemporal & Zygomaticofacial: Supply temple and cheek.
  • Infraorbital Branch: Exits via infraorbital foramen; supplies inferior eyelid, upper lip, and nose.
  • Superior Alveolar Nerves: Posterior, middle, and anterior; supply molars, premolars, canines, and incisors via the gingiva.
  • Pterygopalatine Ganglion Branches: Supply nasal pharynx, soft palate (via Lesser Palatine), hard palate (via Greater Palatine), posterior/superior nasal regions, and nasal cavity.

Path of V3 (Mandibular Division)

• Location: Exits via the foramen ovale.
• Function: Supplies muscles of mastication via SVE fibers.
• Branches:
  • Meningeal Branch (Nervous Spinosus): Runs with the middle meningeal artery.
  • Auriculotemporal Nerve: Supplies external ear and temporal region.
  • Buccal Nerve: Sensory branch to cheek skin.
  • Lingual Nerve: Supplies touch, pain, temperature to the anterior 2/3 of the tongue.
  • Inferior Alveolar Nerve: Runs through mandibular foramen, gives dental branches to teeth and mental nerves to chin skin.
  • Mylohyoid Nerve: Supplies mylohyoid and anterior belly of digastric.
  • Muscles of Mastication Nerves: Deep temporal, masseteric, and lateral pterygoid nerves.
  • Tensor Tympani Nerve: Damper sound during mastication.

Clinical Correlation: Trigeminal Neuralgia

• Cause: Mostly due to compression of the nerve by the superior cerebellar artery (90%), and idiopathic in 10% cases.
• Symptoms: Excruciating, stabbing pain that can radiate across jaw, ear, nose, and eye; lasting seconds to minutes, up to 100 times a day.
• Affected Areas: Mainly V2 (maxillary division) and V3 (mandibular division).
• Treatment:
  • Medications: Carbamazepine, Gabapentin (anticonvulsants).
  • Surgical Options: Microvascular decompression, radiofrequency ablation, and Gamma Knife surgery.