LINEAR MODEL
Desire. In both women and men the desire for sexual activity is also known as
libido. Desire is maintained by a balance between dopamine stimulation and
serotonin inhibition. The threshold of response is determined by androgens,
especially testosterone. This is true for women as well as men.
Excitement. This phase is also known as arousal. It is mediated by
parasympathetic connections to the pelvic organs and results in vascular
engorgement. Arousal in women is generally slower, responds more to touch
and psychic stimuli, and is manifested by vaginal lubrication. Arousal in men is
generally faster, responds more to visual stimuli, and is manifested by penile
erection.
Plateau. This phase entails progression and intensification of the excitement
phase. The length of this phase is variable. The neural pathway and physiologic
mechanism are the same as excitement.
Orgasm. This phase is mediated by sympathetic connections resulting in reflex
tonic-clonic muscle contractions of the pelvic floor followed by contractions of
the uterus. Women have more individual orgasmic variability than men. A
unique characteristic of women is the potential for consecutive multiple
orgasms.
Resolution. This phase is marked by a return to basal physiologic state with
reversal of vasocongestion and muscle tension. Resolution tends to be faster for
men and slower for women.