What does the optic nerve carry?

What does the optic nerve carry?

• A. A bundle of axons carrying signals from photoreceptors directly to the brain.
• B. Retinal ganglion-cell axons from the eye to the optic chiasm.
• C. Bipolar cell axons from the retina to the LGN.
• D. Cones and rods transmitting signals along the optic nerve.

Answer: (B)

The optic nerve carries retinal ganglion-cell axons from the eye to the optic chiasm. Retinal ganglion cells are the output neurons of the retina, and their axons bundle together to form the optic nerve. The signals you see begin with photoreceptors (rods and cones) that connect to bipolar cells, which then synapse onto retinal ganglion cells; only after leaving the retina do these ganglion-cell axons travel toward the brain (becoming myelinated outside the retina) and pass through the optic chiasm, where some fibers cross to the opposite hemisphere. Beyond the chiasm, the signals travel as the optic tract to targets such as the LGN in the thalamus. The other options don’t fit because photoreceptors do not send signals directly to the brain, bipolar cell axons do not form the optic nerve, and cones and rods themselves do not transmit signals along the optic nerve.

The optic nerve carries retinal ganglion-cell axons from the eye to the optic chiasm. Retinal ganglion cells are the output neurons of the retina, and their axons bundle together to form the optic nerve. The signals you see begin with photoreceptors (rods and cones) that connect to bipolar cells, which then synapse onto retinal ganglion cells; only after leaving the retina do these ganglion-cell axons travel toward the brain (becoming myelinated outside the retina) and pass through the optic chiasm, where some fibers cross to the opposite hemisphere. Beyond the chiasm, the signals travel as the optic tract to targets such as the LGN in the thalamus.

The other options don’t fit because photoreceptors do not send signals directly to the brain, bipolar cell axons do not form the optic nerve, and cones and rods themselves do not transmit signals along the optic nerve.