Which cranial nerve is responsible for the Menace reflex?

The Menace reflex is a specific eye reflex that involves the coordination between visual input and motor output. The primary cranial nerve responsible for initiating the Menace reflex is the optic nerve, also known as cranial nerve II (CN 2). This reflex is tested by presenting a quickly approaching object to the eye, which should elicit a blink response.

The action begins with CN 2, which transmits visual information from the retina to the brain. When the object is perceived, the visual signal is processed, and the response is sent to the facial nerve, cranial nerve VII (CN 7), which controls the muscles of facial expression, including those responsible for blinking.

Though other cranial nerves may be involved in the reflex pathway—such as CN 5, which provides sensory innervation to the cornea and plays a role in the blink reflex—the initial and crucial sensory input is provided specifically by CN 2. Therefore, recognizing the function of CN 2 is essential, as it is the nerve that detects the visual stimulus that triggers the Menace reflex.