Most mammalian species lose less endometrial tissue

during menstruation. Most mammalian species lose less endometrial tissue
than humans do and thus do not menstruate. (B) In males, sperm originate in the
testes, mature in the adjacent epididymis, and are expelled during ejaculation via
the muscular vas deferens. Along the way, structures such as the seminal vesi
and prostate gland add their secretions, forming semen.
phallus The clitoris or penis.
(A) Male
Orgasm
Time
(B) Female
-:
\
Time
gasm, and resolution (FIGURE 12.9). During the excitement phase, the phallus (tr
penis in men, the clitoris in women) becomes engorged with blood, making it erect
In women, parasympathetic activity during the excitement phase causes change*
in vaginal blood vessels, resulting in the production of lu-
bricating fluids that facilitate intromission. Stimulation a
the penis, clitoris, and vagina during rhythmic thrusting
accompanying intromission may lead to orgasm. In borr
men and women, orgasm is accompanied by waves of con-
tractions of genital muscles (mediating ejaculation in mer
and contractions of the uterus and vagina in women).
In spite of some basic similarities, the sexual respor -
es of men and women differ in important ways. For
thing, women show a much greater variety of commonh
observed copulatory sequences. Whereas men have only
one basic pattern, captured by the linear model of Mas-
ters and Johnson (FIGURE 12.9A), women have at k: •
three typical patterns (FIGURE 12.9B). Another impor-
tant aspect of human sexuality is that most men, but not
most women, have an absolute refractory period follow-
ing orgasm (see Figure 12.9A). That is, most men can-
12.9 HUMAN SEXUAL RESPONSE PATTERNS
(A) The typical male pattern includes an absolute
refractory period after orgasm, which may be fol-
lowed by renewed arousal (dotted line). (B) These
three patterns (A, B, C) are often observed in women.
These diagrams are schematic and do not represent a
particular physiological measure, although heart rate
varies in roughly this manner. The patterns vary con-
siderably from one individual to another. (After Masters
and Johnson, 1966.)
I 380 CHAPTER 12

•ot achieve full erection and another orgasm until some
hne has elapsed—the length of time varying from min-
tes to hours, depending on individual differences and
nther factors. Many women, on the other hand, can have
•ultiple orgasms in rapid succession. Functional imag-
ing of the brains of men and women during sexual activ-
ty suggests that, although the brain circuitry associated
with orgasm itself is quite similar between the sexes (a
topic we return to at the end of this chapter), substan-
tially different networks are active in men's and women's
brains during sexual activity prior to orgasm (Georgiadis
etal.,2009).
Taking a broader perspective on sexuality reveals ad-
ditional distinctions between men and women (Peplau,
D03). Research has generally found that basic sex drive
is greater in men, reflected in more frequent masturba-
fion, sexual fantasies, and pursuit of sexual contacts.