Most of us know how things go when getting intimate. But did you know there's actually a scientific order to what's going on in our bodies, enough so that we can classify each stage of it?
Masters & Johnson (William and Virginia) came up with the first three stages of excitement, plateau and orgasm. According to wikipedia, Masters hired Johnson to help him in a study about human sexuality (he later left his wife for Johnson, but it didn't last. They divorced in 1992). Helen Singer Kaplan added a fourth stage to their diagram--the resolution stage. This was big because sexual dysfunction is classified in the 4th edition of the DSM (Diagnostic and Statistical Manual) based on this diagram--it is a dysfunction if it interrupts any stage. What are the stages?
Step 1: Excitement
Step 2: Plateau
Step 3: Orgasm
This is the shortest stage. Fore-play and the sexual arousal stages can last really as long as you want them to, but orgasms are always just a matter of time-stopping, blissful, relieving seconds. The muscles all release their tension and start to contract. There is a rapid increase of oxygen, and all the levels from the previous stages (blood pressure, heart rate, breathing) are at their fastest. Women's uterus and vagina contract, and the base of the penis contracts. Most of the time, this causes ejaculation in men, and in some women (men actually can orgasm without ejaculating). Some people get something called a 'sex flush'-they turn a light red almost everywhere on the body, but mostly on the stomach and genitals.
Step 4: Resolution
One psychologist, Basson, has stated that whereas this model makes sense, it may differ between women and men. Not all women have an orgasm during sex (sure, men might not either, but the percentage of women who don't faaaar exceed the men). Masters&Johnson's model is considered 'a linear' model, but Basson claims it should be circular. Their model is linear because it assumes that a person follows each stage one by one, from step one to step four. But not everyone starts off in the excitment stage, and not everyone ends in the resolution stage. Assuming the stages go as planned, this is what happens.