![]() ![]() 436), a disorder of oligodendrocyte myelin. Common signs and symptoms of damage to the other cranial nerves include difficulty chewing, nasal regurgitation, slurred speech. If cranial nerve IX is injured, it can lead to difficulty swallowing and a reduced gag reflex. CN V is also ensheathed by oligodendrocyte-derived, rather than Schwann cell–derived, myelin for up to 7 mm after it leaves the brainstem, unlike just a few millimeters for other cranial and spinal nerves this may explain the high frequency of trigeminal neuralgia in multiple sclerosis (MS) (Chap. For example, cranial nerve IX (the glossopharyngeal nerve) is involved in salivation, swallowing, and the gag reflex. In the brainstem, the spinal tract of V is also located adjacent to crossed ascending fibers of the spinothalamic tract, producing a “crossed” sensory loss for pain and temperature (ipsilateral face, contralateral arm/trunk/leg) with lesions of the lateral lower brainstem. Upon entering the pons, pain and temperature fibers descend ipsilaterally to the upper cervical spinal cord as the spinal tract of V, before synapsing with the spinal nucleus of V this accounts for the facial numbness that can occur with spinal cord lesions above C2. The cornea is primarily innervated by V1, although an inferior crescent may be V2. The trigeminal nerve is predominantly sensory, and motor innervation is exclusively carried in V3. V1 and V2 traverse the cavernous sinus to exit in the superior orbital fissure and foramen rotundum, located above and below the eye socket respectively V3 exits through the foramen ovale. It exits in the lateral midpons and traverses the middle cranial fossa to the semilunar (gasserian, trigeminal) ganglion in Meckel’s cave, where the nerve divides into three divisions (ophthalmic, maxillary, and mandibular ). The motor part innervates the muscles involved in chewing (including masseters and pterygoids) as well as the tensor tympani of the middle ear (hearing especially for high-pitched tones). The trigeminal (fifth cranial) nerve supplies sensation to the skin of the face and anterior half of the head (Fig. ![]()
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