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Chapter 7: Head

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A 25-year-old male undergoes emergency surgery to repair an internal carotid thrombosis following a gunshot injury in the right carotid triangle. Following the procedure, the patient exhibits miosis (pupillary constriction) and partial ptosis (drooping) of the right upper and lower eyelids. Which structure is injured?

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A. C4 spinal cord

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B. Ciliary ganglion

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C. Frontal nerve

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D. Internal carotid plexus

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E. Oculomotor nerve (CN III)

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Answer D. Sympathetic fibers supply the dilator pupillae and the tarsal muscles. Postganglionic sympathetic fibers originate in the superior cervical ganglion and join the internal carotid (periarterial) plexus. The ophthalmic branch of the internal carotid artery carries postganglionic sympathetic fibers into the orbit. The pupil was constricted due to interruption of the oculosympathetic pathway and the resulting unopposed action of the constrictor pupillae muscle (innervated by parasympathetic fibers). Partial ptosis was due to sympathetic interruption to the tarsal muscles.

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A 44-year-old man is admitted to the emergency department with multiple facial contusions after a fight. Physical examination fails to detect any visual defects (e.g., loss of vision or double vision). However, there is a loss of sensation from the cornea. Which nerve is most likely injured?

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A. Frontal

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B. Infra-orbital

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C. Nasociliary

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D. Oculomotor (CN III)

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E. Optic (CN II)

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Answer C. The nasociliary nerve, a branch of the ophthalmic division of the trigeminal nerve (CN V1), provides sensory innervation to the eye. These sensory axons reach the eye through two pathways: (1) directly through long ciliary nerves or (2) indirectly via the ciliary ganglion (no synapse) and short ciliary nerves.

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A 30-year-old female presents in the ophthalmology clinic complaining of double vision (diplopia). The extra-ocular muscles are assessed using the "H-test." Upon left gaze (i.e., patient looking to their left), the right (adducted) eye "drifts" upward into elevation. Lesion of which nerve on the affected side would cause the observed eye movement defect?

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A. Abducent nerve (CN VI)

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B. Inferior branch of the oculomotor nerve (CN III)

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C. Superior branch of the oculomotor nerve (CN III)

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D. Trochlear nerve (CN IV)

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E. None of the above

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Answer E. The trochlear nerve innervates the superior oblique ...

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