Sexual desire is often defined as a desire or want to experience sexual feelings and/or activities, intimacy or gratification without or with a partner(s). There are many influences on sexual desire and it is achieved differently for different people. The concept of this is referred to as the human sexual response cycle. The human sexual response cycle, sexual desire, activities, satisfaction, and physical and mental responses in men and women are different. Men usually feel sexual satisfaction during sexual activity and are more prone to physical attraction, whereas women are more affected by the environment and emotions related to the sexual partner or sexual fantasy in terms of sexual satisfaction.
Men generally respond to visual sexual stimuli, such as attractive nude or erotic pictures, or erotic films. Women respond differently to the same sexual stimuli. Some women feel repulsed by muscular, erotic male photos, and some are sexually attracted by emotional or lingual stimulation. Psychologic and biologic factors influence the brain's appraisal and processing of sexual stimuli to allow or disallow subsequent arousal. The sexual and non-sexual outcomes influence motivation to future sexual intimacy.
The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution. Both men and women experience these phases, although the timing usually is different. Thanks to WebMd, I have provided some brief descriptions of each phase:
Phase 1: Excitement
Muscle tension increases.
Heart rate quickens and breathing is accelerated
Nipples become hardened or erect.
Vaginal lubrication begins.
The woman's breasts become fuller and the vaginal walls begin to swell.
The man's testicles swell, their scrotum tightens and begin secreting a lubricating liquid.
Phase 2: Plateau
The changes begun in phase 1 are intensified.
Muscle spasms may begin in the feet, face, and hands.
Muscle tension increases.
The woman's clitoris becomes highly sensitive (may even be painful to touch) and retracts under the clitoral hood to avoid direct stimulation from the penis.
Phase 3: Orgasm
Involuntary muscle contractions begin.
In women, the muscles of the vagina contract. The uterus also undergoes rhythmic contractions.
A rush, or "sex flush" may appear over the entire body.
Blood pressure, heart rate, and breathing are at their highest rates, with a rapid intake of oxygen.
Phase 4: Resolution
The body slowly returns to its normal level of functioning, and swelled and erect body parts return to their previous size and color.
When a male enters the resolution phase, they lose their erection and experiences what is called the refractory period. This is the period of time it takes for a male to experience another erection. The duration of the refractory period usually increases with age and/or other medical conditions.
Females do not experience a refractory period; they may be sexually aroused again quickly.
For a variety of reasons, sexual responses can be negatively affected. Check out some of the ones I came across through research:
You may have problems getting erections. As men get older, it usually takes longer to get a full erection. With aging, erections may not get as firm as they were at a younger age. This is normal.
You may have less desire for sex due to stress at work, school, or home. You may be tired, depressed, or angry. You may get an erection when you do not want one.
You may feel like you either reach orgasm too soon or that it takes too long.
You may feel that you or your partner is not getting enough enjoyment out of sex.
Your ideas about good sex may be different from your partner’s.
Depression or anxiety
Heart and blood vessel disease
Neurological conditions, such as spinal cord injury or multiple sclerosis
Gynecological conditions, such as vulvovaginal atrophy, infections or lichen sclerosus
Certain medications, such as antidepressants or high blood pressure medications
Emotional or psychological stress, especially with regard to your relationship with your partner
A history of sexual abuse