Tuesday, April 29, 2008

The Human Sexual Response

Sex is an enormous part of our lives as humans, complete with its own rules, etiquette, and ritual. It requires such intense emotional investment that it is often easy to forget that sex is really just a biological function intended to advance our species. In their 1966 book Human Sexual Response, researchers William Masters and Virginia Johnson reveal four generally accepted biological stages of sexual response. You may know it as getting? it on!

1. Stage One: Excitement

  • Increasing level of muscle tension

  • Quickened heart rate

  • Flushed skin or blotches of redness on the chest and back

  • Hardened or erect nipples

  • Vasocongestion: the swelling of the woman's clitoris and labia minora; erection of the man's penis

Vagina lubricatesCowper’s gland lubricates
Uterus elevates and growsTesticles elevate and swell
Breasts and vagina swellScrotal sac tightens
Pubococygeal muscle (surrounding vaginal opening) tightens

The readiness of a woman's body for orgasm is called the "orgasmic platform" by Masters and Johnson, hence foreplay! A man doesn't need to climb to an ?orgasmic platform,? his excitement levels leap to plateau and beyond far more quickly than a woman?s.

2. Stage Two: Plateau

This is the intensification of all of the changes begun during the excitement phase. Plateau is basically the having of the sex! This intense excitement is what couples try to prolong; sensitive body parts will be doubly sensitive during this period. After an hour or six, depending on the couple, the plateau phase evolves to the verge of orgasm, prompting the reversal of the excitement phase.

3. Stage Three: Orgasm

That's right, the big O. This is the peak of sexual excitement, the culmination of plateau.

  • Involuntary muscle contractions

  • Heightened blood pressure and heart rate

  • Rapid intake of oxygen

  • Sphincter muscle contraction

  • Spasms of the carpopedel muscles (feet)

  • Sudden forceful release of sexual tension

Rhythmic uterus muscle contractionsEmission phase: Seminal fluid builds up in the urethral bulb of the prostate gland
Tightening of the woman's muscles assists in male orgasmThe fluid accumulates and the male senses he is about to ejaculate
Muscle contractions in the uterus and pelvic areas open the way for the man’s spermUrinary bladder closes to block the possibility of urine mixing with
semen—urine would kill the helpless sperm!
Expulsion phase: Rhythmic contraction expels semen

Orgasm, or 'coming,' is, by nature, extremely pleasurable. The more the human animal indulges this pleasure, the more likely it becomes that the sex act will result in offspring. Kind of takes all the fun out of it, huh? Enter contraception.

4. Stage Four: Resolution

  • A return to normal heart rate, blood pressure, breathing, and muscle contraction

  • Swelled and erect body parts return to normal

  • Skin flushing disappears.

  • General sense of security and enhanced intimacy

  • Possible fatigue

You may recognize this stage as afterglow. Women are often capable of returning to stage three rapidly, and enjoying orgasm repeatedly with minimal stimulation for up to an hour! Are you getting the most out of your biological functions? Thank you, come again.

Men, on the other hand, have to wait anywhere from a few minutes to several days to have another orgasm, especially as they age. This is called a refractory period by Masters and Johnson, and though partial or full erection may be sustained, men cannot achieve orgasm during the refractory period. Refractory periods fluctuate greatly among men.

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