The endocannabinoid system (ECS) acts to moderate the functioning of numerous body elements. Science describes this consistent physiological function as homeostasis. Endocannabinoids activate receptors on the surface of cells, and this activation works as a feedback loop or to change cell behavior.
Research has found two major cannabinoid receptors: CB1 and CB2 (sometimes written as CB1R and CB2R). Research has found other receptors, but these are the most studied.
Research finds CB1 receptors throughout the body but are most abundant in the brain and spinal cord neurons. CB2 receptors occur outside of the nervous system on immune system white blood cells and to a lesser extent throughout the body.
The ECS shows the intriguing relationship between the brain and the immune system, as well as the rest of the body. The brain and nervous system use molecules for communication. The signaling molecules flow from one cell to receptors on the outside membrane of other cells. Parts of the body also signal each other with molecules called hormones. One may argue that the ECS is a hormonal system in that the endocannabinoids circulate with the blood, rather than being secreted into a synapse as with most neurotransmitters.
Another curious aspect relates to how similar CB1 and CB2 are to each other. All receptors consist of protein. Cells make proteins according to the genetic code, translating nucleic acid sequences into amino acid strands. Protein strands draw from the body’s 20 amino acids, but the sequence is critical for the protein to fold into a form that provides a function. The folding often takes the form of a helix, a winding coil.
CB1 and CB2 only have 44% of sequence homology with each other. That means that the two sequences originated as a single sequence very far in the past but have undergone extensive mutation since that time. And yet, they retain that 44% similarity which usually means the sequences that are critical to function are maintained (mutations are lethal). (In progress; more to come...) ///