Cranial Nerves: Classification and Clinical Relevance - Anatomy and Physiology

1. Which cranial nerves form the afferent and efferent limbs of the pupillary light reflex?

   Afferent: optic nerve (CN II). Efferent: oculomotor nerve (CN III), whose parasympathetic fibers constrict the pupil.

2. A patient has a drooping eyelid, a dilated pupil, and an eye resting in a down and out position. Which cranial nerve is affected?

   The oculomotor nerve (CN III). It supplies the levator palpebrae, most extraocular muscles, and parasympathetic fibers that constrict the pupil.

3. Which cranial nerve carries motor fibers to the muscles of mastication and general sensation from the face?

   The trigeminal nerve (CN V).

4. A patient suddenly cannot raise the eyebrow, close the eye, or smile on one side of the face. Which cranial nerve is affected?

   The facial nerve (CN VII), which supplies the muscles of facial expression. This pattern is typical of Bell palsy.

5. Which cranial nerve innervates the sternocleidomastoid and trapezius muscles?

   The accessory nerve (CN XI).

6. Which cranial nerve innervates the superior oblique muscle of the eye?

   The trochlear nerve (CN IV).

7. After a lower motor neuron lesion, a patient's tongue deviates to the right when protruded. Which nerve is damaged, on which side?

   The right hypoglossal nerve (CN XII). The intact left genioglossus pushes the tongue toward the weak right side.

8. Which cranial nerve provides most of the parasympathetic innervation to the thoracic and abdominal viscera?

   The vagus nerve (CN X).

9. Which cranial nerves form the afferent and efferent limbs of the corneal blink reflex?

   Afferent: trigeminal nerve (CN V, ophthalmic division). Efferent: facial nerve (CN VII), which closes the eyelids.

10. Which cranial nerve carries taste from the anterior two-thirds of the tongue?

    The facial nerve (CN VII), through its chorda tympani branch. Taste from the posterior third travels in the glossopharyngeal nerve (CN IX).

11. Which cranial nerve innervates the lateral rectus muscle, and what eye movement is lost when it is damaged?

    The abducens nerve (CN VI). Damage prevents abduction, so the eye cannot turn outward past midline.

12. Which three cranial nerves are classified as purely sensory?

    Olfactory (I), optic (II), and vestibulocochlear (VIII).

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