Phototransduction summary: Change in voltage occurs in which structure; Change in the concentration of what in the synapse; Change in the membrane potential of the post-synaptic cells; Change in the release of what at the next synaptic terminal?

• A. rods, neurotransmitter, membrane potential, neurotransmitter
• B. cones, calcium, membrane potential, acetylcholine
• C. rods, ions, postsynaptic potential, GABA
• D. rods, neurotransmitter, current, neurotransmitter

Answer: (A)

In phototransduction, light makes the photoreceptor itself change its voltage, with rod cells hyperpolarizing in light. This means the voltage change occurs in the photoreceptor structure. The signal in the synapse is carried by the neurotransmitter; in darkness rods continuously release neurotransmitter, and light reduces that release, so the concentration of neurotransmitter in the synapse changes. That change in transmitter level then affects the postsynaptic cells, altering their membrane potential. Finally, the signal continues to the next terminal via release of the same neurotransmitter, which governs how the next neuron is activated. This sequence aligns with rods as the structure, neurotransmitter as the synaptic substance, postsynaptic membrane potential as the response in the next neuron, and neurotransmitter release as the signal carried onward.