Overview of Cranial Nerves Snapshot A 66-year-old woman presents with worsening double vision and a mild headache. She denies any head injury, vision loss, or jaw claudications. Medical history is significant for hypertension, hyperlipidemia, and type II diabetes mellitus. On physical exam, she has right-sided ptosis, conjugate gaze, and impaired extraocular movement of the right eye except with right lateral gaze. The pupils are round and reactive to light. (Ischemic injury leading to a third-nerve palsy with sparing of the pupils) Muscles Innervated by Cranial Nerves Cranial Nerve Muscle(s) Lesion(s) Oculomotor nerve (CN III) Extraocular muscles innervated by CN III are superior rectus (SR) infecrior rectus (IR) medial rectus (MR) inferior oblique (IO) Levator palpebraesuperioris Ciliary muscle Sphincter pupillae Diplopia Ptosis Loss of accomodation Pupillary involvement in compressive lesions the pupil becomes dilated and non-reactive in ischemic lesions (e.g., diabetes mellitus) the pupil is spared Trochlear nerve (CN IV) Superior oblique Difficulty looking down Head tilt away from the side of the lesion Mandibular branch of the trigeminal nerve (CN V3) Muscles of mastication include masseter temporalis lateral and medial pterygoid Anterior belly of the diagstric muscle Mylohyoid muscle Tensor palati Tensor tympani Jaw deviation towards the side of the lesion Abducens nerve (CN VI) Lateral rectus Horizontal diplopia Facial nerve (CN VII) Muscles of facial expression Posterior belly of digastric muscle Stylohyoid muscle Stapedius muscle Bell's palsy Loss of blink reflex Hyperacusis (when the stapedius is involved) Glossopharyngeal nerve (CN IX) Stylopharyngeus muscle - Vagus nerve (CN X) Muscles of the palate and pharynx except tensor palati muscle (CN V3) Stylopharyngeus muscle (CN IX) All muscles of the larynx Palate droop Dysphagia Deviation of the uvula away from the side of the lesion Loss of gag reflex (the sensory component of this reflex is mostly via CN IX) Accessory nerve (CN XI) Sternocleidomastoid muscle Trapezius muscle Weakness with turning of the head Shoulder droop Hypoglossal nerve (CN XII) Muscles of the tongue except for the palatoglossus muscles Tongue deviation towards the side of the lesion