Which nerve is primarily responsible for vision?

The optic nerve is the primary nerve responsible for vision in both humans and horses. It is the second cranial nerve, designated as cranial nerve II, and plays a critical role in transmitting visual information from the retina in the eye to the brain. The optic nerve carries signals from photoreceptors in the retina, which respond to light and enable the perception of images, color, and movement.

This connection is vital for the visual processing that occurs in the brain, allowing organisms to interpret their surroundings and respond appropriately.

In contrast, the other nerves listed do not have a primary role in vision. For example, the hypoglossal nerve is primarily responsible for controlling the movements of the tongue, while the vagus nerve has functions related to the autonomic control of the heart, lungs, and digestive tract. The spinal accessory nerve is involved in neck and shoulder movement. Thus, the optic nerve's dedicated function in the visual system distinguishes it as the correct answer regarding which nerve primarily governs vision.