Also, I had a question about the rods and action potentials. I'm sorry about all these questions.
In the green book, it says rods that are exposed to light have their rhodopsin broken down into opsin and retinal. This bleaching means that Na+ channels are closed, but Na+ is still actively pumped out causing the rod cell to enter a state of hyperpolarisation. This hyperpolarisation is a generator potential in the rod which, if large enough to reach the threshold, will allow neurotransmitter substance to enter into the synapse which will stimulate an action potential at the bipolar cell.
The orange book, however, says that the state of hyperpolarisation in the rod cell means no neurotransmitter (glutamate) is released, and this leads to an action potential occuring in the rod cell.
I'm confused about the role of the neurotransmitter. The orange book also says neurotransmitter is released when rods are exposed to darkness, which prevents an action potential occuring.