Cranial Nerves + The Eye PDF

CN V: Trigeminal Nerve Function: General somatic sensory → Skin, mucous membranes and sinuses of the whole face Special visceral motor → V3 supplies the muscles of mastication and 4 others There are also parasympathetic fibres that run with branches of the trigeminal nerve Course: Originate f...

CN V: Trigeminal Nerve Function: General somatic sensory → Skin, mucous membranes and sinuses of the whole face Special visceral motor → V3 supplies the muscles of mastication and 4 others There are also parasympathetic fibres that run with branches of the trigeminal nerve Course: Originate from 4 nuclei (3 sensory, 1 motor) ○ Mesencephalic (sensory) ○ Principal sensory (sensory) ○ Spinal nucleus of the trigeminal nerve (sensory) ○ Motor nucleus of the trigeminal nerve (motor) The three sensory nuclei merge into a sensory root at the pons This then becomes the trigeminal ganglion in the middle cranial fossa which gives rise to 3 divisions: ○ Ophthalmic (V1) → Superior orbital fissure ○ Maxillary (V2) → Foramen rotundum ○ Mandibular (V3) → Foramen ovale The motor root passes inferiorly to the sensory root and merges with V3 only CN V1: Ophthalmic Branch From the trigeminal ganglion, V1 travels through the cavernous sinus then exits the cranium via the superior orbital fissure before dividing into 3 terminal branches Frontal nerve (largest branch, divides in two) - sensory only ○ Supraorbital → upper eyelid and conjunctiva, scalp ○ Supratrochlear → upper eyelid and conjunctiva, forehead Lacrimal nerve (smallest branch) - sensory + parasympathetic ○ Sensory innervation of the lacrimal gland ○ Parasympathetic fibres from the facial nerve (VII) synapse at the pterygopalatine ganglion and travel with the zygomatic branch of V2, then the lacrimal branch of V1 Nasociliary nerve - sensory + sympathetic ○ Long ciliary → cornea + sympathetic fibres to dilator pupillae (from the superior cervical ganglion) ○ Anterior ethmoid → frontal, ethmoid and sphenoid sinuses, nasal cavity ○ Posterior ethmoid → sphenoid sinus (absent in 30%) ○ Infratrochlear → bridge of nose, upper eyelid and conjunctiva Note the ophthalmic nerve itself does not contain autonomic fibres, fibres from other nerves “hitchhike” CN V2: Maxillary Branch From the trigeminal ganglion, V2 travels through the cavernous sinus then exits the cranium via the foramen rotundum before giving rise to many branches (don’t memorise them) : Function: Sensory innervation to: ○ Lower eyelid and its conjunctiva ○ Inferior posterior portion of the nasal cavity ○ Lateral nose ○ Cheeks and maxillary sinus ○ Upper lip, teeth, gingiva and palate Parasympathetic innervation to: ○ Lacrimal gland (VII → V2 zygomatic branch → V1) ○ Mucous glands of the nasal mucosa (VII → V2 nasopalatine and greater palatine) ○ Again, these fibres do not originate from the trigeminal nerve CN V3: Mandibular Branch From the trigeminal ganglion, V3 exits the cranial cavity through the foramen ovale, passing through the infratemporal fossa to give rise to 4 sensory branches: Auriculotemporal nerve (actually the convergence of two separate roots) ○ Superior root → Sensory fibres → Anterior auricle, external acoustic meatus and tympanic membrane Lateral temple ○ Inferior root → Parasympathetic fibres from CN IX → Otic ganglion → Parotid Buccal → Sensory fibres only ○ Buccal membranes of the mouth (cheek) ○ 2nd and 3rd molar teeth Inferior Alveolar → Sensory and motor ○ Mylohyoid branch → Motor nerve to mylohyoid and anterior digastric ○ Remaining sensory fibres run through the mandibular canal to supply the mandibular teeth ○ After emerging from the mental foramen it becomes the mental nerve → sensation to lower lip and chin Lingual Nerve → Sensory only ○ General sensory fibres → Anterior ⅔ of tongue ○ Special sensory fibres (taste) to the anterior ⅔ of tongue is from CN VII but travels with lingual ○ Autonomic fibres from CN VII also follow lingual → submandibular ganglion → submandibular and sublingual glands CN V3: Mandibular Branch V3 is the only branch of trigeminal to conduct motor axons. The motor root joins just after the trigeminal ganglion and supplies: Muscles of mastication ○ Masseter ○ Medial and lateral pterygoid ○ Temporalis Tensor tympani - dampens sounds by stabilising the malleus Tensor veli palatini - elevates the soft palate to prevent regurgitation of food Suprahyoid muscles - elevate the hyoid bone during swallowing ○ Anterior belly of digastric ○ Mylohyoid CN V: Trigeminal Nerve Pathology Trigeminal Neuralgia Herpes Zoster Chronic neuropathic pain over the distribution HSV can lie dormant in the trigeminal nerve of the trigeminal nerve ganglion Two types: Shingles = reactivation of the virus ○ Hyperalgesia - increased sensitivity to pain Painful blistering vesicles appear in the ○ Allodynia - pain from a non-painful stimulus (e.g. distribution of a branch unilaterally (V1 most light touch) Caused by nerve damage commonly) ○ Multiple sclerosis ○ Stroke ○ Trauma Treatment: Carbamazepine (anticonvulsant) to reduce nervous transmission of the pain ○ Typical analgesics do not work ○ If unresponsive to carbamazepine, surgical destruction of the nerve is possible but results in permanent loss of sensation to the area CN V: Trigeminal Nerve Blocks Infraorbital: Anaesthetises upper lip and maxillary incisor teeth Mental: Anaesthetises lower lip and chin Buccal: Anaesthetises cheek Inferior alveolar: Anaesthetises mandibular teeth and tongue (due to close proximity to the lingual nerve)