What is the main action of the Ophthalmic Nerve (CN V1)?

The main action of the Ophthalmic Nerve, which is the first division of the trigeminal nerve (CN V1), is sensory innervation. It provides sensation from the cornea, which is crucial for protecting the eye and maintaining clarity of vision, as well as from the skin of the forehead. This sensory function is essential for detecting touch, pain, and temperature changes in these areas.

CN V1 branches into several important pathways, including the frontal nerve, which further divides into the suprachoroidal nerve and the infratrochlear nerve, supplying sensations to the forehead, upper eyelid, and parts of the nose. This extensive sensory network is vital for reflex responses such as blinking when the cornea is touched.

Other options involve different cranial nerves with distinct functions. For instance, motor control of the lateral rectus muscle is attributed to the abducens nerve (CN VI), which is responsible for lateral eye movement. Similarly, balance and sensation from the semicircular ducts is the role of the vestibulocochlear nerve (CN VIII), while motor control of the muscles of facial expression is primarily managed by the facial nerve (CN VII). Hence, option B accurately identifies the primary sensory role of the Ophthalmic