 Have we ever talked about receptors before? Yes, it's because they're that important. And here's the deal. If a cell does not have a cellular receptor, then it's not going to be able to pick up the information. Period. Done. If you're lacking the receptor, you can't read the message. The message is going to bounce right off of you. For example, if I have a green chemical message, a hormone that came in and is going to function on this cell, and I have a receptor that I tried to make it look like, this receptor is going to fit this chemical message, then the receptor can bind, we can get the message. If I have another chemical message that comes along that looks like this, and I agree that this chemical message might come in, it certainly isn't going to bind to this receptor. They don't have the same shape. It might bind if there was a receptor that looked like this. That would total, like, then we've got the message. But if that receptor is missing, then this little chemical message is not going to be read. Like, who cares if you send out that message? I'm not going to listen to you. Act of binding, a chemical message binding with a receptor can do all sorts of things. It can stimulate something called a second message cascade, and there's a reason that I draw the second messenger cascade like this. A second messenger cascade is this cascade of chemical reactions, and there are things like this chemical, the binding of the receptor with the initiating signal will cause this molecule to turn into, okay, I can't help it, this molecule, and cause that molecule to turn into this molecule, and then that molecule is going to turn into this molecule, and then that one's going to turn into this molecule, and that's going to end up with this molecule, which actually is the, that's what you needed in the first place, and this one is going to go do something. Here's what's true in Wendy Land. We could memorize every single one of those. We could totally, and sometimes I get kind of fired up, and I'm like, oh, don't you want to know? Like, what is this molecule right here, and how did it turn into this one right here, and what else got outed to turn it into this one? But most of the time, I'm just going to say a molecule binds with the receptor, stimulates a second message cascade, and this is the result. We will end up with maybe an enzyme that will go do something. That receptor allows the action to take place. This process is called signal transduction, and all that is, is, it's communication. It's cellular communication. It's taking this signal and transducing it to get something done. Oh my gosh, it's almost like there's a pathway inside the cell. This little cellular receptor is my, like my little sensory receptor, and the signal is like my little, my little stimulus, and then this is like my little pathway. There's not really an integrator in this little scenario, but here is an efferent effector that can make something happen. Do you see, like, it's a really important process to understand how actions happen. How does your cell, how to do that? Well, this is an example of a possible mechanism for making it happen. This is fantastic. Signaling molecules combine to receptors and cause channels to open. It causes channels to close, which then can send an electrical message somewhere. It's actually really, really fantastic. So you can imagine that we can fine-tune our ability to communicate with each other by, what? By, by being really thoughtful about what's going on with the receptors. So now we're going to look at specific things that can do with receptors to allow us to receive certain kinds of information. It's almost like, you know, if I'm sitting in my office and I want to be able to see, so I'm looking out my window and I want to know if somebody's coming around, but I don't want to be able to hear all that. So I put in earplugs. I've said you can't communicate with me by sound. So whatever's going on out there, I'm not going to listen. So I'm going to lack a receptor for a certain kind of signal. But I do want to know if you're standing out there like waving at me. And so I'm going to keep a different kind of receptor available on the cell. And every cell is going to come up with its own, like depending on what its needs are, it's going to come up with its own strategy for how to use receptors. Holy cow, you ready for this? Okay, so let's look at how we can use receptors to receive information that we need.