Page 226-262, 36 pages Page 1 of15
Chapter 9: Sexual Response
THE SEXUAL RESPONSE CYCLE
• Researchers Masters & Johnson provided one of the first models of the physiology of human sexual
response, from observations of over 10,000 sexual cycles of arousal and orgasm in 382 women and 312
• Sexual response typically progresses in three stages: excitement, orgasm, and resolution. This uses
two basic physiological processes: vasocongestion when a great deal of blood flows into the blood
vessels of the genitals due to vasodilation, and myotonia with muscle contraction in the genitals and
throughout the body.
• Limitations: Descriptive, not explanatory; focus on physiology and not psychology aspects of arousal
• Excitement: The beginning of erotic arousal marked by vasocongestion.
• In men, this produces an erection when the corpora cavernosa and the corpus spongiosum fill with
• Vasodilation of the arteries supplying the corpora must occur, while veins carrying blood away from the
penis must compress to restrict outgoing blood flow. Nitric oxide (NO) is particularly involved in
vasodilation by causing smooth muscle relaxation, and is acted on by Viagra.
• Erection can be produced by direct physical stimulation of the genitals, by stimulation of other parts of
the body, or by erotic thoughts. Vasocongestion can occur rapidly within seconds, although it may be
slowed by factors like age, alcohol intake, and fatigue.
• As the man gets closer to orgasm, fluid secreted by the Cowper’s gland appear at the meatus, and may
contain active sperm although it is not ejaculate.
• The skin of the scrotum thickens, the scrotal sac tensing to be pulled closer to the body as the
spermatic cords shorten. Vasocongestion and myotonia continue to build until there is sufficient tension
• The reverse process of vasoconstriction occurs for an erection to soften following orgasm, in the
resolution phase. The neurotransmitters epinephrine and norepinephrine are involved.
• In women, an important response is vagina lubrication, also resulting from vasocongestion as the
capillaries in the walls of the vagina dilate, so fluid can move through these semipermeable membranes.
This response is slightly less rapid than men’s, beginning 10-30 seconds after the onset of arousing
stimuli. Estrogen helps vasodilation
• Orgasmic platform is the tightening of the entrance of the vagina caused by contractions of the
bulbospongiosus muscle, which covers the vestibular bulbs, that occurs late in the arousal stage for
females. This may result in a noticeable increase in gripping of the penis.
• The glans of the clitoris swells, from engorgement of the corpora cavernosa, felt larger and harder
than usual. The crura of the clitoris deeper in the body also swells, as do the vestibular bulbs along the
walls of the vagina.
• The clitoris may elevate, retracting or drawing up into the body. The inner lips swell and open up,
uncovering the entrance to the vagina.
• The nipples also become erect due to myotonia of muscle fibres surrounding the nipples, and the
breasts swell and enlarge due to vasocongestion – nipples may look somewhat flatter due to breast
swelling Page 226-262, 36 pages Page 2 of 15
• In the unaroused state, the walls of the vagina lie against each other like an uninflated balloon. During
excitement, the upper 2/3 expand dramatically in ballooning to accommodate penetration, pulling up the
cervix and uterus.
• A sex flush may appear on both men and women, with reddening of the skin on the upper abdomen
and chest. There is also an increase in pulse rate and blood pressure.
• Orgasm is the second stage of sexual response, an intense sensation which occurs at the peak of
sexual arousal and is followed by release of sexual tension.
• Sharp increase in pulse, blood pressure, and breathing rate. Muscles contract throughout the body, with
the feet and hands in carpopedal spasms, and the face may be contorted in a grimace.
• In men, orgasm consists of a series of rhythmic contractions of the pelvic organs at 0.8 second intervals
• In the preliminary stage, the vas, seminal vesicles, and prostate contract; this forces the ejaculate into a
bulb at the base of the urethra. This creates the sensation of ejaculatory inevitability, that it is about to
happen and cannot be stopped.
• In the second stage, the urethral bulb, muscles at the base of the penis, and the urethra contract
rhythmically, forcing the semen through the urethra and out through the meatus.
• Some researchers have shown that ejaculation and the sensation of orgasm can be dissociated, and
that the feelings of pleasure and satisfaction from orgasm relate more strongly to psychological and
social factors than physical factors.
• Also a series of rhythmic muscular contractions, 3 or 4 in a mild orgasm or as many as a dozen in a
very intense, prolonged orgasm. The uterus also contracts rhythmically.
• Women typically do not reach orgasm as quickly as men do, and some women may think they are
having an orgasm when they are not, mistaking intense arousal for orgasm.
• Main feeling is a spreading sensation that moves from the clitoris through the whole pelvis, more
intense than a warm glow or pleasant tingling. The woman may feel the contraction of the muscles
around the vaginal entrance.
• Except for women who experience fluid emission, female orgasm typically leaves no tangible evidence.
• There is a cultural skepticism about female orgasm, and women sometimes fake orgasm. It may be
difficult for women to orgasm, or the woman may feel she is expected to have an orgasm due to cultural
• Good, honest communication and avoidance of performance goals can help.
• Resolution: Third stage of sexual response, in which body returns to the physiologically unaroused
state. This includes the reversal of processes that build up during excitement, such as vasocongestion.
Pulse rate, blood pressure, and breathing rate all decrease.
• In women, the first change is a reduction in the swelling of the breasts. The clitoris returns to its normal
position, then shrinks to its normal size. The orgasmic platform relaxes and shrinks. This phase usually
takes 15-30 minutes, and may take longer in women who did not achieve orgasm.
• In men, there is detumescence where the corpora cavernosa first empties quickly, then the corpus
spongiosum and glans empty slowly, leading to loss of erection in the penis.
• Men enter a refractory period, where they are incapable of being aroused again, gain an erection, or
have an orgasm. This varies between individuals from a few minutes to 24 hours, growing longer with
• Women usually do not have a refractory period, so they can experience multiple orgasms. Page 226-262, 36 pages Page 3 of15
• Oxytocin is secreted during sexual arousal, while a surge of prolactin occurs at orgasm in both men
and women. Prolactin may be the off-switch to sexual arousal and create refractory period in males.
Much more prolactin is secreted following orgasm from intercourse than orgasm from masturbation.
More on Women’s Orgasms
• Clitoral Orgasm: Freud’s term for orgasm in the female resulting from clitoral stimulation. Vaginal
orgasm: Freud’s term for orgasm in the female resulting from stimulation of the vagina in heterosexual
• Freud believed the vaginal orgasm to be more developmentally “mature”, shifting erogenous zone from
clitoris to vagina after the Oedipal stage.
• This interpretation of vaginal orgasms led many women to undertake psychoanalysis and agonize why
they were not able to achieve vaginal orgasm. Those who could only have clitoral orgasms were called
“vaginally frigid” or “fixated” at an infantile stage.
• According to Masters & Johnson, there is no difference between the two. Physiologically, all female
orgasms are the same regardless of site of stimulation – some women could orgasm solely through
• Second, clitoral stimulation is almost always involved even during vaginal intercourse, with its deep
structures stimulated through the vaginal entrance.
• However, research has found that different parts of the brain are activated during clitoral and vaginal
• Masters & Johnson also discovered that women can achieve multiple orgasms within a short time with
continued stimulation, with each being physiologically identical to single orgasms (they are not minor or
• After resolution, women do not usually enter a refractory period, perhaps because it takes longer for
vasocongestion to return to baseline in women than in men.
• Multiple orgasm with a partner is more likely to result from hand-genital or mouth-genital stimulation
than from intercourse. Through masturbation, women may have 5-20 orgasms; when a vibrator is used
and less physical effort is needed, some women are capable of having 50 orgasms in a row!
• Some men may also be capable of having multiple orgasms. In these men, detumescence did not
always occur following an orgasm, allowing for continued stimulation; certain orgasms would ejaculation
and others would not.
• 3 different models for women: Similar to men’s but without refractory period; lack of orgasm with
with orgasm and
• Masters &
ignores cognitive and subjective aspects of sexual response – desire, passion, and subjective qualities of
arousal and orgasm, as well as context and quality of relationship in which sexual contact occurs
(pleasure, satisfaction, intimacy, etc.)
• Women tend to emphasize subjective arousal over physical, often unrelated to genital awareness. Page 226-262, 36 pages Page 4 of15
• There was also a selection bias where participants needed to have a history of orgasm through both
masturbation and coitus – those who did not experience orgasm or who do not have consistent levels of
sexual desire were excluded. Therefore this may not be generalizable
to the entire population.
Singer-Kaplan’s Triphasic Model
• Triphasic Model: Thinking of sexual response as three relatively
independent components – sexual desire, vasocongestion, and
muscular contractions. Sexual desire adds a cognitive component.
• 1) The two physiological components are controlled by different
parts of the nervous system, vasocongestion by the parasympathetic
autonomic system, and ejaculation and orgasm by sympathetic.
• 2) These two components also involve different anatomical structures: blood vessels and muscles.
• 3) They differ in susceptibility to being disturbed by injury, drugs, or age. Refractory period lengthens
with age for men, resulting in decrease in frequency of orgasm. In contrast, capacity for erection
• 4) Reflex of ejaculation can be brought under voluntary control, but erection reflex cannot.
• 5) Impairment of vasocongestion response or the orgasm response produce different and separate
sexual disturbances in terms of erection problems, rapid ejaculation, or delayed ejaculation.
• Limitations: Suggests desire must precede sexual excitement, does not account for multiple orgasms,
and assumes men and women have similar sexual responses – may lead to pathologization of lack of
orgasm in women
The Intimacy Model
• Female sexual function proceeds in more complex, circuitous manner than male sexual functioning.
Particularly influenced by psychosocial factors, such as relationship satisfaction, self-image, and
• Circular intimacy-based model of sexual
response, arguing that women in long-term
relationships may not be motivated to engage in
sexual behaviour by experience of spontaneous
• Rather, they are motivated to enhance
emotional intimacy, closeness, and
commitment, and to share physical sexual
• They thus begin the activity in a sexually neutral
state, but are receptive to sexual stimuli that will
arouse them. This leads to sexual desire and
• Many points of vulnerability in the cycle
Whalen & Roth’s Cognitive Model
• Cognitive Model: Starts with
perception of a stimulus as
sexual. If perceived positively,
will generate arousal.
• Awareness of arousal, the
evaluation positively will feedback into arousal, maintaining arousal response. This leads to sexual
behaviour, which is perceived and evaluated again – arousal is maintained continually. Page 226-262, 36 pages Page 5 of 15
• Limitations: Is this realistic, no orgasm or resolution phase to end the loop
Dual Control Model
• Dual Control Model: Sexual response is controlled by both sexual excitation and sexual inhibition.
Sexual response can be a powerful distraction that may become disadvantageous or dangerous in
certain situations, so the existence of an inhibition process id advantageous.
• Individuals differ in propensities toward excitement and inhibition. Problems can occur at the extremes
– people who are very high on excitation and low on inhibition can engage in high-risk sexual behaviours,
while vice versa people may be more likely to develop sexual disorders.
• Scales to measure these tendencies include excitation items such as “When I think of a very attractive
person, I easily become sexually aroused” and inhibition items like “Putting on a condom can cause me
to lose my erection”
• Early learning and culture are critical, determining which stimuli the individual will find to be exciting
or inhibiting. For example, media communicate standards of what sexually attractive women are
supposed to look like.
• Inhibition is adaptive: environment may not be conducive to reproduction, better to wait for a better day
or season, e.g. fertility reduced during drought and famine.
• Excessive sexual behaviour in fact reduces fertility in men, as body cannot produce sperm quickly
enough for a high sperm count in each ejaculation.
Emotion & Arousal
• No one has proposed a formal model of emotion and arousal, but one study examined such effects
• Daily diary method for couples, asked to fill it out separately with questions on emotions and sexual
• Positive emotions showed strong positive association with reports of sexual arousal, but negative
emotions also positively correlated! This may be because anxiety and anger involve generalized
arousal, and intensify arousal responses to sexual stimuli.
HORMONAL & NEURAL BASES OF SEXUAL BEHAVIOUR
The Brain, the Spinal Cord, and Sex
• The brain and spinal cord have important interacting functions in sexual response
• Erection and ejaculation are controlled by spinal cord reflexes.
• A reflex has 3 basic components: receptors which are sensory neurons that detect stimuli and transmit
the message to the spinal cord; transmitters which are centres in the spinal cord that receive the
message, interpret it, and send out a message for the appropriate response; effectors, neurons or
muscles which respond to the stimulation.
Mechanism of Erection
• Tactile stimulation of the penis, and its receptor neurons, or nearby regions such as the scrotum or
thights produce a neural signal transmitted to the erection centre in the sacral spinal cord.
• This sends a message via the parasympathetic system to the muscles around the arteries in the penis,
causing them to relax; the arteries can thus expand, be filled with blood, and produce erection. The
valves and compression of the veins also reduce blood outflow.
• Men who have had spinal cord injuries at a level above the reflex centre can still have erections and
• Erection can also be produced by fantasy or other purely psychological factors in the brain
Mechanism of Ejaculation Page 226-262, 36 pages Page 6 of15
• The penis responds to stimulation by sending a signal to the two ejaculation centres, located in the
lumbar section. This message is relayed to the sympathetic system, triggering muscle contractions in the
internal organs involved in ejaculation.
• Ejaculation can be controlled voluntarily, highlighting the importance of brain influences.
• Retrograde Ejaculation: Ejaculate, rather than going out through the tip of the penis, empties into the
bladder. A dry orgasm results. This can be caused by some illnesses, drugs used to treat psychoses, and
by prostate surgery.
• An internal sphincter closes off the entrance to the bladder, while an external sphincter opens during
ejaculation allowing semen outflow through the penis. In retrograde ejaculation, the actions of these two
sphincters are desynchronized: the external one closes and the internal one opens, instead.
• The condition is harmless, though some men are disturbed by the lack of semen emission
Mechanisms in Women
• Sensory input travels along dorsal nerve of clitoris, then along the pudendal nerve to a reflex centre in
the sacral spinal cord. In rats, this urethrogenital reflex results in muscle contractions similar to orgasm in
• The clitoris and vagina are both supplied by sympathetic and parasympathetic nerves.
• The Gräfenberg spot (G-spot) is also called the Skene’s glands, or female prostate. It is located on
the top side of the vagina halfway between the pubic bone and cervix. Its ducts open into the urethra,
and is responsible for the fluid some women emit during orgasm (female ejaculation).
• Continued stimulation of the G-spot produces a uterine orgasm, characterized by deeper sensations
of uterine contractions than the clitorally-induced vulvar orgasm.
• This ejaculate contains prostate-specific antigen (PSA) just like that produced by the male prostate.
• About 40% of women report having experienced ejaculation at orgasm at least once, and 66% report
having an especially sensitive area near the G-spot.
Brain Control of Sexual Responses
• Sexual responses can be brought under voluntary control and initiated by purely psychological forces;
also influenced by environmental factors, such as learning or culture.
• The most important brain influence comes from the limbic system, which includes the amygdala,
hippocampus, cingulate gyrus, fornix, and septum. The thalamus, pituitary, and reticular formation are
also closely connected.
• The anterior hypothalamus, particularly the medial preoptic area (MPOA), is implicated in male sexual
behaviour. When electrically stimulated, male rats increase sexual behaviour; when lesioned, they fail to
engage in copulation
• The paraventricular nucleus (PVN) of the hypothalamus fires when the genitals are stroked; PVN
neurons project down to the spinal cord to sexual reflex
• Men shown erotic films had high activation of the limbic
structure by fMRI – insula involved in sensory processing,
cingulate cortex in attentional processes and guiding
responsiveness, amygdala in sexual responding and
• For individuals with spinal cord injury, brain regions are
activated through the vagus nerves
Hormones & Sex
Organizing vs. Activating Effects Page 226-262, 36 pages Page 7 of 15
• Organizing Effects: Effects of sex hormones early in development during critical periods, resulting in a
permanent change in the brain or reproductive system, including creating male or female genitals.
• Activating Effects: Effects of sex hormones in adulthood, resulting in activation of sexual behaviours
and aggressive behaviours.
• Pregnant female guinea pigs injected with testosterone had offspring which were incapable of
displaying female sexual behaviours, particularly lordosis, sexual posturing with arching of back and
raising of hindquarters. This may be because the testosterone organized brain tissue in a male fashion;
these female offspring were also born with masculinized genitals. Rather, they displayed masculine
sexual behaviours such as mounting.
• With males, castration at birth and administration of ovarian hormones in adulthood resulted in female
• Seems like males and females initially have capacities for both male and female sexual behaviours
depending on both organizing and activating hormones.
• For humans, sexual behaviour is less under hormonal control and more under high brain neural control.
Testosterone & Sexual Desire
• Men deprived of testosterone by castration or illness have dramatic decrease in sexual behaviour,
decrease in sexual desire with anti-androgens.
• However, sexual behaviour may decline very slowly or be present for years after castration –
importance of experience and brain control in humans.
• Levels of testosterone correlated with sexual behaviour in male puberty. Of those with testosterone in
highest quartile, 69% had engaged in sexual intercourse by grade 10; for the lowest quartile, only 16%
had. Thus, at puberty, testosterone affects sexual motivation directly.
• Androgens are also related to sexual desire in some women. Women who have undergone
oophorectomy typically due to cancer have marked decrease in sexual desire, which increases if treated
with testosterone (such as DHEA, a pre-testosterone hormone)
• Eunuch: A castrated man. Men may take anti-androgens for chemical castration to treat advanced