Sexual physiology: the Western medicine view
Sexual response is a coordinated sequence of vascular, neural, hormonal, and psychological changes. Understanding this helps you recognize when the body is working normally and when to see a doctor.
Updated November 14, 2026Compiled by UK MASTER ACADEMYFor readers aged 18 and over
- Western medicine describes sexual response through four successive phases: excitement, plateau, orgasm, and resolution.
- In men, erection occurs when parasympathetic nerves release nitric oxide, relaxing smooth muscle in the corpus cavernosum and increasing blood flow to the penis.
- In women, stimulation increases circulation to the clitoris and vaginal walls, producing engorgement and lubricating fluid through a similar mechanism.
- Dysfunction at any point, from vascular to psychological, can affect the response and warrants specialist evaluation.
The four phases of sexual response
In 1966, William Masters and Virginia Johnson published a model describing human sexual response through four observable phases:
- Excitement: the body begins to respond to stimulation. Men develop an erection; women experience clitoral engorgement and vaginal lubrication.
- Plateau: the aroused state is maintained and intensifies. Heart rate, blood pressure, and breathing all increase.
- Orgasm: rhythmic contractions in the pelvic region, in smooth muscle and pelvic floor muscles. In men, ejaculation accompanies this phase.
- Resolution: the body gradually returns to its resting state. Men have a brief refractory period before they can respond again.
This model laid the foundation for modern sexual physiology research. However, later studies have shown that women's response often does not follow this linear sequence.
Basson's circular model for women
In 2001, Rosemary Basson proposed a model specifically for women, based on an assessment of 47 individuals with desire concerns. The model is circular rather than linear, beginning from a state of physiological neutrality.
According to Basson, women often seek or accept sexual stimulation for non-biological reasons, such as a desire for emotional closeness. Appropriate stimulation within a positive context then leads to subjective arousal. Arousal in turn reinforces motivation for the next encounter, completing the circle.
The research noted that psychological factors reduced the capacity for arousal in 85% of participants, and depression contributed in 43%. This shows that psychology and relational context play a central role, no less important than physiology.
In men too, many authors emphasize that emotional and cognitive factors influence the entire response cycle, not only the excitement phase.
The role of blood vessels and nerves
In men
Erection is a vascular reflex coordinated by the nervous system. When stimulation is received, the parasympathetic nervous system releases nitric oxide in the corpus cavernosum. Nitric oxide relaxes smooth muscle, allowing blood to fill the tissue and be retained by compressed outflow veins, creating an erection.
Ejaculation is controlled by the sympathetic nervous system, coordinated with rhythmic pelvic floor muscle contractions.
Erectile dysfunction can arise from: vascular damage due to atherosclerosis or diabetes, nerve damage, hormonal imbalance, or psychological factors.
In women
A similar mechanism occurs in women: stimulation increases blood flow to the clitoris and vaginal walls. The clitoris becomes engorged, and lubricating fluid is secreted through the vaginal wall by filtration pressure from dilated blood vessels.
The parasympathetic nervous system is responsible for initial arousal. The sympathetic nervous system participates in orgasm along with rhythmic pelvic floor contractions.
Estrogen maintains the elasticity and blood supply of vaginal tissue. When estrogen declines after menopause, the tissue thins and lubrication decreases.
The role of hormones
Testosterone is the key hormone for sexual desire in both men and women. In men, testosterone is necessary for the development and maintenance of reproductive function, including penile nerve sensitivity to nitric oxide. In women, testosterone levels are much lower but also contribute to desire and arousal.
Estrogen in women maintains vaginal tissue, supports lubrication, and protects the mucosa. When estrogen falls, lubrication decreases and tissue becomes thinner and more prone to irritation.
Oxytocin rises during intimate contact and after orgasm, contributing to the feeling of connection. Prolactin rises after orgasm and is associated with the sense of satisfaction and the refractory period.
Chronically elevated cortisol from ongoing stress can suppress both testosterone and sexual response, which is the mechanism by which stress affects physiology.
The pelvic floor and psychology
The pelvic floor muscles participate directly in orgasm through rhythmic contractions. These muscles also support erection in men by compressing venous outflow. When pelvic floor muscles are either too weak or too tense, both conditions can cause functional problems. See the article Kegel exercises for men.
Psychology is an inseparable component. Anxiety, stress, depression, and negative body image can all impair the response by activating the sympathetic nervous system, causing vasoconstriction and inhibiting arousal. Basson's research noted psychological factors in 85% of people with desire concerns.
Relationship and context also matter considerably. Feelings of safety, trust, and emotional connection affect response quality, particularly in women according to Basson's model.
When to see a doctor
See a specialist when:
- Erectile dysfunction or low libido persists for more than three months without a clear reason such as temporary stress.
- Difficulty with lubrication, pain during sex, or inability to reach orgasm despite repeated attempts.
- Symptoms appear after starting a new medication or following a newly diagnosed medical condition.
See the full list of signs and appropriate specialties at the article When to see a doctor.
Questions and answers
What is the four-phase model of Masters and Johnson?
This model was proposed by William Masters and Virginia Johnson in 1966. It divides sexual response into four successive phases: excitement, plateau, orgasm, and resolution. The model describes observable physiological changes in both men and women.
How does Basson's model for women differ?
Basson's model (2001) shows that sexual response in women is often not linear but circular, beginning with a motivation for intimacy, then seeking stimulation and experiencing arousal. Psychological and relational factors play a central role.
What does nitric oxide have to do with erection?
Parasympathetic nerves release nitric oxide, which relaxes smooth muscle in the corpus cavernosum, allowing blood to fill it and creating an erection. When blood vessels are damaged by diabetes or atherosclerosis, this process is impaired.
Why can erectile dysfunction signal cardiovascular disease?
The blood vessels supplying the penis are smaller in diameter than the coronary arteries. When atherosclerosis begins, the penis is often affected first. Persistent erectile dysfunction may therefore be an early sign of cardiovascular disease, according to the Princeton III Consensus recommendations.
Sources
- Basson R. Human sexual response. Handbook of Clinical Neurology. 2015;130:11-18. PubMed 26003236
- Basson R. Using a different model for female sexual response to address women's problematic low sexual desire. Journal of Sex and Marital Therapy. 2001;27(5):395-403. PubMed 11554199
- Baumann F, Hehli D, Makaloski V, et al. Erectile dysfunction - overview from a cardiovascular perspective. Vasa. 2017;46(5):347-353. PubMed 28486869
- Nehra A, Jackson G, Miner M, et al. The Princeton III Consensus recommendations for the management of erectile dysfunction and cardiovascular disease. Mayo Clinic Proceedings. 2012;87(8):766-778. PubMed 22862865
This page is general health information compiled from international medical sources. It has not been reviewed by a physician and is not a diagnosis or a treatment instruction. The content is for readers aged 18 and over. If symptoms persist, please see a doctor.