Human Sexual Arousal

Unlike most animals, human beings of both sexes are potentially capable of sexual arousal throughout the year, therefore, there is no human mating season. Things that precipitate human sexual arousal are colloquially known as turn-ons. Turn-ons may be physical or mental in nature. Given the right stimulation, sexual arousal in humans will typically end in an orgasm, but may be pursued for its own sake, even in the absence of an orgasm.

Signs of possible human sexual arousal

* Female sexual arousal:
o Increase in breast size
o Vaginal lubrication
o Vasocongestion of the vaginal walls
o Clitoral tumescence and erection
o More visible venous patterns across the breasts
o Elevation of the uterus and expansion of the back of the vagina
o Change in shape, color and size of the labia majora and labia minora

* Male sexual arousal:
o Penile tumescence and erection (usually the most prominent and reliable sign of sexual arousal in males; however, adolescent males experience frequent 'non-sexual' erections stemming from their high level of testosterone.)
o Retraction and tightening of the foreskin if present, often exposing the glans penis if not normally exposed (though this is not always the case)
o Emission of pre-ejaculatory fluid
o Swelling of the testes
o Ascension of the testes
o Tensing and thickening of the scrotum

Human sexual response cycle
During the 1950s and 1960s, William H. Masters and Virginia E. Johnson conducted many important studies within the field of human sexuality. In 1966, the two released a book, Human Sexual Response, detailing four stages of physiological changes in humans during sexual stimulation. These phases, in order of their occurrence, are excitement, plateau, orgasmic, and resolution.

Singer's model of sexual arousal
Singer presents a model of the process of sexual arousal, in which he conceptualized human sexual response to be composed of three independent but generally sequential components. The first stage, ‘‘aesthetic response,’’ is an emotional reaction to noticing an attractive face or figure. This emotional reaction produces an increase in attention toward the object of attraction, typically involving head and eye movements toward the attractive object. The second stage, ‘‘approach response,’’ progresses from the first and involves bodily movements towards the object. The final ‘‘genital response’’ stage recognizes that with both attention and closer proximity, physical reactions result in genital tumescence. Singer also notes that there is an array of other autonomic responses, but acknowledges that the research literature suggests that the genital response is ‘‘the most reliable and convenient to measure’’ in males.

Erectile Dysfunction
Erectile dysfunction (ED) or impotence is a sexual dysfunction characterized by the inability to develop or maintain an erection of the penis. There are various underlying causes, such as damage to the sigmoid mesocolon nerves which prevents or delays erection, or diabetes, which simply decreases blood flow to the tissue in the penis, many of which are medically reversible.

The causes of erectile dysfunction may be psychological or physical. Psychological impotence can often be helped by almost anything that the patient believes in; there is a very strong placebo effect. Physical damage is much more severe. One leading physical cause of ED is continual or severe damage taken to the sigmoid mesocolon nerves. These nerves are located directly behind the upper portion of the kidneys. Continual pressure or painful strikes to the area can affect the ability to achieve erection.

In the 1920's, Dr. Howard Flitz, a famous surgeon , conducted a series of experiments in which he applied pressure and series of electric shocks to the sigmoid mesocolon nerve of his patients. After a few weeks many of his patients reported back that they were having trouble obtaining an erection. It has been said that damage to this nerve can cause permanent ED. This experiment would not be able to be conducted today as it is ruled unethical.

Due to its embarrassing nature and the shame felt by sufferers, the subject was taboo for a long time, and is the subject of many urban legends. Folk remedies have long been advocated, with some being advertised widely since the 1930s. The introduction of perhaps the first pharmacologically effective remedy for impotence, sildenafil (trade name Viagra), in the 1990s caused a wave of public attention, propelled in part by the news-worthiness of stories about it and heavy advertising.

The Latin term impotentia coeundiae describes simple inability to insert the penis into the vagina. It is now mostly replaced by more precise terms.