What are OFF-bipolar cells?

What are OFF-bipolar cells?

• A. Cells activated by neurotransmitter release, inhibiting ganglion cells
• B. Cells activated when neurotransmitter fails, leading to ganglion cell firing
• C. Cells that synthesize myelin around the optic nerve
• D. Cells that absorb stray light

Answer: (A)

OFF-bipolar cells carry the signal for the OFF (decrease in light) pathway. In the dark, photoreceptors continuously release glutamate. OFF-bipolar cells have ionotropic glutamate receptors (AMPA/kainate) that respond to glutamate with depolarization, so they become active and excite OFF ganglion cells. When light increases, glutamate release falls, the OFF-bipolar cells hyperpolarize, and the OFF ganglion cells reduce their firing. So these cells are activated by the neurotransmitter released by photoreceptors and they convey excitatory signals to downstream ganglion cells in darkness; they do not inhibit ganglion cells.

OFF-bipolar cells carry the signal for the OFF (decrease in light) pathway. In the dark, photoreceptors continuously release glutamate. OFF-bipolar cells have ionotropic glutamate receptors (AMPA/kainate) that respond to glutamate with depolarization, so they become active and excite OFF ganglion cells. When light increases, glutamate release falls, the OFF-bipolar cells hyperpolarize, and the OFF ganglion cells reduce their firing. So these cells are activated by the neurotransmitter released by photoreceptors and they convey excitatory signals to downstream ganglion cells in darkness; they do not inhibit ganglion cells.