Human Sexual Response Cycle

Masters and Johnson's Human Sexual Response Cycle

  • Focuses on the physical changes during sexual arousal.
  • Based on direct observation of individuals engaging in sexual activity in the laboratory, hooked up to physiological recording equipment.

Measurements

  • Penile Strain Gauge:
    • Placed around the circumference of the penis.
    • Measures the increase in circumference as the penis becomes erect.
  • Vaginal Photoplethysmograph:
    • Inserted into the vagina (resembles a tampon).
    • Measures the amount of light reflected off the vaginal walls.
    • Increased blood flow (vasocongestion) darkens the vaginal walls, reducing light reflection.

Four Phases of Masters and Johnson's Human Sexual Response Cycle

  1. Excitement
  2. Plateau
  3. Orgasm
  4. Resolution

Key Terms

  • Vasocongestion: Blood flow to the genitals.
  • Myotonia: Muscle tension.

Model Overview

  • Men and women go through the same four stages, but with unique differences.
1. Excitement Phase
  • Increase in vasocongestion leading to swelling of genitals.
    • Women:
      • Clitoris swells in diameter and length.
      • Vagina lubricates, expands, and lengthens, becoming darker in color.
      • Major and minor labia thicken.
    • Men:
      • Penis becomes erect.
      • Scrotal skin tenses and thickens.
      • Testes elevate slightly within the scrotum.
  • Increase in myotonia (muscle tension) for both men and women.
  • Heart rate and blood pressure begin to rise for both sexes.
2. Plateau Phase
  • Relatively constant state of arousal.
  • Orgasmic Platform (Women):
    • Vasocongestion swells the tissues of the outer third of the vagina.
    • Vaginal opening contracts to grip the penis ensuring ejaculation occurs inside the vagina in order to ensure fertility.
    • Tenting: Inner part of the vagina expands fully, almost like a deflated balloon when a woman is not sexually aroused.
    • Uterus elevates.
  • Clitoris retracts under the prepuce (can cause concern for couples in sex therapy).
  • Further increase in muscular tension, respiration rate, heart rate, and blood pressure.
  • Sex Flush:
    • Skin on the chest and abdomen becomes more red (due to blood flow).
    • Occurs in about a quarter of men and three-quarters of women.
3. Orgasm Phase
  • Muscular contractions in the body.
  • Men reach the point of ejaculatory inevitability (orgasm occurs even if stimulation stops).
  • If stimulation stops for women before orgasm, the orgasm stops.
  • Possible loss of voluntary muscle control (spasms).
  • Blood pressure, respiration rates, and heart rates reach their peak.
  • Women can have multiple orgasms (achieving orgasm more than once without arousal level dropping below the plateau level).
  • Men experience a refractory period, preventing multiple orgasms.
4. Resolution Phase
  • Reversal of vasocongestion and myotonia.
  • Blood flows out of the genitals, returning them to their non-aroused state.
  • Erections are due to blood flow, not bone.
  • Muscles become less tense.
  • Disappearance of the sex flush (if present).
  • Respiration, heart rate, and blood pressure return to normal.
  • Orgasmic Platform Resolution (Women):
    • Uterus lowers to its regular position.
    • Cervical opening widens for 20-30 minutes, allowing easier entry for sperm and to ensure fertilization of an egg.
    • The tenting of the vagina creates a pool for the semen, and the uterus is lowered into it.
  • Refractory Period (Men):
    • Physiologically incapable of achieving another orgasm.
    • Must return to the pre-plateau level of arousal.
    • Length of time depends on age (adolescents vs. men over 50).
When Orgasm Does Not Occur
  • Men may experience "blue balls" due to engorged testicles.
  • Vasocongestion reverses, with blood flowing out of the genitals.
  • Cold showers can help speed up the process (vasovagal response, blood rushes to internal organs).
  • Same process occurs in women, though it may be less noticeable.

Kaplan's Model of Human Sexual Response

  • Overlaps with Masters and Johnson's model but consists of three stages.
  • The most important difference between Kaplan's model and Masters and Johnson's model is the desire phase.
  1. Desire
  2. Excitement
  3. Orgasm
  • The desire phase is psychological in nature, preceding the body's physiological response to arousal.
  • Adds a psychological component that precedes those physiological changes.
  • Of particular importance for individuals experiencing sexual dysfunction.