in this video we will go over the definition of a receptive field and how the light is transduce and encoded via on and off center bipolar and ganglion cells receptive fields are groups of photoreceptors that send inputs to a particular bipolar cell or retinal ganglion cell which will then pass the information on to the brain cones and rods are the photoreceptors that respond to light in the retina on and off Center receptive fields have different responses to light based on differences in the bipolar cells in humans photoreceptors hyperpolarize in response to light due to opsins breaking down in their receptor photoreceptors only respond with graded potentials and release glutamate proportionally to the level of depolarization so when the receptor hyperpolarizes in light it will release less glutamate both on and off center bipolar cells have different responses to glutamate based on the glutamate receptors on each cell the on center bipolar cells have metabotropic glutamate receptors while the off center bipolar cells have ionotropic glutamate receptors for Oncenter cells these metabotropic glutamate receptors will hyperpolarize the cell in response to glutamate in the light the bipolar cell receives less glutamate from the photoreceptors therefore allowing it to depolarize and release more glutamate in the dark the bipolar cell will receive more glutamate from the photoreceptors therefore making it hyperpolarize and release less glutamate due to the response of the metabotropic receptor off-center bipolar cells have the opposite response to glutamate because they have ionotropic glutamate receptors when glutamate binds to the receptor it will open potassium channels causing potassium to flow out of the off-center bipolar cell depolarizing it as the membrane potential increases creating a graded potential in the bipolar cell in the light the bipolar cell will receive less glutamate from the photoreceptors therefore making it hyperpolarize and release less glutamate in the dark the bipolar cell will receive more glutamate from the photoreceptors therefore making it depolarize and released more glutamate the more glutamate that is released on to the corresponding ganglion cell from its bipolar cell the more action potentials it will fire in response the opposite responses of the on center and off-center bipolar cells is the key to the differential response to light when photoreceptors hyperpolarize in response to light they release less glutamate which will cause a greater response from the on Center cells since they depolarize when there is less glutamate while causing a lower response from the off Center cells since they hyperpolarize when there's less glutamate the surround of the receptive field also influences the amount of glutamate released by the photoreceptors if the surround is dark the photo sur receptors in this round will depolarize just as a normal photo receptor does causing them to release more glutamate onto the hyper horizontal cell that it is connected to this horizontal cell will depolarize in response to the glutamate and release its own inhibitory neurotransmitter known as glycine glycine will further inhibit the center photoreceptor causing it to release even less glutamate this situation will create the highest response in the on centric ganglion cell since it prefers conditions of lower glutamate due to its metabotropic receptors the opposite happens when the surround is light the photoreceptor will hyperpolarize in the surround causing it to release less glutamate onto the horizontal cell which will then in turn release less glycine allowing the central photoreceptor to not be inhibited and release even more glutamate this is a situation that will cause the highest response in an off-center ganglion cell or off-center bipolar cell the key to this difference rests solely in the on and off center cells due to their different receptors each bipolar cell will correspond to a ganglion cell that will show the same pattern as depolarization or hyperpolarization as the bipolar cell so if the deep bipolar cell is highly depolarized then the ganglion cell itself will also be depolarized and fire at many action potentials let's go through a couple of examples of receptive field firing responses using an off Center bipolar cell in Figure B we can see the optimal highest response of the off-center cell which occurs when there is dark in the center and light in the surround dark in the center causes the highest depolarization rate of the off-center bipolar cells as we saw in previous slides therefore causing the most action potentials in its ganglia so that's the optimal response for the center the light also causes less inhibition of the central of the central photoreceptor therefore also conforming to that optimal condition for that key blue that cell so we're going to put two check marks here because this is the best condition for this off-center cell for maximal firing then we can compare other lighting examples to this template of the optimal firing condition to determine the approximate firing rate for example on number on figure a we can see that the center is light and does not match the dark spot seen in the optimal firing condition for the off-center cell so we can put an X there because it doesn't match in this around we see matching conditions to the optimal right so the off-center cell likes there to be light in this around so you put a check there so we've one check and one X which leads us to believe that the off-center cell would have a more medial firing rate in this condition which we do see in the ganglion cell outputs shown here we can do a similar comparison for example see so that the center matches the optimal firing rate which is having a dark spot in the center this year-round however does not match the optimal firing rate which has light in this round so we'll put an X here so we have one checkmark in one X based on this we'll expect a medial firing rate which again we do see you can take each of these examples and continue to compare them to the optimal firing rate in any situation for on and off center cells to determine the approximate firing rate please leave any questions about receptive fields on an off-center bipolar cells and ganglion cells in the comments and I'll try to answer them soon good luck studying