What composes the optic nerve?

• A. Bipolar cell axons
• B. Photoreceptor axons
• C. Amacrine cell axons
• D. Ganglion cell axons

Answer: (D)

Signals from the retina are carried toward the brain by the axons that make up the optic nerve. This nerve is formed specifically by the axons of retinal ganglion cells as they bunch together at the optic disc and exit the eye. Photoreceptors (rods and cones) detect light and pass their signal to bipolar cells; their axons stay within the retina and do not form the optic nerve. Amacrine cells are interneurons that help process signals within the inner retina, and their axons don’t contribute to the optic nerve. Bipolar cells transmit signals from photoreceptors to ganglion cells, but their axons also stay in the retina. So, the optic nerve is composed of ganglion cell axons.