Now, in many cases so it's not shown in this diagram, but it's shown in this diagram. And we'll talk about that in just a moment. In many cases, the seven TM domain actually contains additional protein domains attached onto the intracellular side of that structure, as we see in this particular case. And those additional structures play very important, very specific roles. So now let's move on to the epinephrine signaling pathway. So in the epinephrine signal transduction pathway, the epinephrine is that primary messenger and binds into a special region of a protein we call the beta adrenergic receptor, the beta AR, which is a type of seven TM receptors.