The Science of Orgasm

Afferent (sensory input) nerves (pairs) (genitals => brain)
pelvic nerve (骨盆神经): vagina, cervix, rectum, urinary bladder // spinal cord lower lumbar level
pudendal nerve (阴部神经): clitoris, labia(majora+minora) / penis (penile skin) + scrotum (阴囊) (合称 perigenital skin) // spinal cord upper sacral level (S2-S4)
hypogastric nerve(下腹部神经): cervix, uterus / prostate(前列腺), testes(睾丸)。控制ejaculation // sympathetic chain, spinal cord thoracic level (T10-T12)
vagus nerve (迷走神经): cervix, uterus.新近发现。不通过脊椎(spinal cord)传导到大脑。所以高位截瘫的女性仍可能有性体验/性高潮


breast, nipple: sensory activity from the breast traveling (“projecting”) to certain of the same group of neurons in the brain that receives sensory activity from the genitals
  * 特别是 paraventricular nucleus (室旁核) of the hypothalamus (下丘脑)。接受刺激分泌催产素

cervix: pelvic, pudendal, hypogastric

刺激任何单个神经对应的区域都可能产生 orgasm (of different feelings)。同时刺激涉及多种神经的多个区域可以产生更强烈的 "blended orgasm" (additive effect).
orgasms resulting from vaginal stimulation: deep,heaving

male orgasm is known to be necessary for male re-productive success, while the same is not true for women.

orgasm: 1分钟内开始释放大量 oxytocin。一般认为 Oxytocin 促进子宫收缩。
oxytocin (neurohormone)
* 促使乳腺肌肉收缩导致分泌乳汁
* 促使子宫平滑肌(uterine smooth muscle)收缩
* 分娩时胎儿通过宫颈时也会通过骨盆神经刺激分泌催产素。

inductive evidence (of evolutionary adaptive significance of female orgasm)

oxytocin, released in peak levels during orgasm in women, produces a dramatic increase in uterine peristaltic movement, which propels sperm selectively into the particular fallopiantube (left or right) that receives the ovum during that particular menstrual cycle

Corpus cavernosum penis (plural corpora cavernosa) 阴茎海绵体

male sexual arousal: 物理或认知刺激(penis or psychogenic (cognitively induced)) 引起副交感神经 parasympathetic nerves 反应，导致 erection。
  * 目前认为副交感神经由室旁核里的催产素分泌细胞(oxytocinergic neurons)的刺激引起反应。
  * oxytocinergic neurons: neurons that communicate with other neurons by releasing oxytocin as their chemical transmitter. central nervous system => 外周神经的单向信号传输(descending)
  * 注意在这个过程种，催产素作为神经递质(neurotransmitter)发挥作用。而不是通常的作为分泌的激素(hormone)进入血液。

Reflexively sexual arousal (mechanical stimulation of the penis): the sensory signals are transmitted into the spinal cord, where they stimulate output via the nerves projecting to the penis.
Cognitively sexual arousal: the brain sends neural signals down the spinal cord and out via the same nerves to the penis.

sperm capacitation 精子获能。the process that renders sperm capable of fertilizing an egg

vaginal epithelium 上皮组织

androgen. n.雄性激素；男性荷尔蒙.女性里由卵巢和adrenal cortex(副腎皮質)分泌。主要引起性欲。

orgasms are good for your health, except in a small percentage of men (and perhaps women?) with heart disease.

Multiple Sclerosis (MS)  多发性硬化症

dopamine: key neurotransmitter involved in stimulating orgasm in humans.
  * acts more as a neuromodulator of sensory input. (produces a sensitization to sensory stimuli): Dopaminergic drugs fail to produce orgasm by themselves
Dopaminergic drugs: drugs that increase dopaminergic activity (agonists, releasers, or uptake inhibitors)
  * cocaine:

Serotonin: plays an essential role in the inhibitory regulation of orgasm.
  * 由 serotonin 2(A) receptors 影响。

dopamine 和 Serotonin 神经递质构成动态平衡。

neuroleptics (NL, 神经阻滞剂): a broad category of antipsychotic drugs)
antidepressants:
  * selective serotonin reuptake inhibitors (SSRIs).
  * Bupropion: 安非他酮；丁氨苯丙酮. Like cocaine, it blocks the dopamine reuptake mechanism, thereby increasing the level of dopamine in the synapse.

Marijuana: 含有多种 cannabinoid (麻黄素)成分
amphetamine (安非他命): 中枢神经刺激剂(Psychostimulants)，用来治疗注意力不足过动症、嗜睡症、和肥胖症。被作为致幻剂使用。have mental effects similar to those of cocaine, although the state of euphoria is less intense.
Cocaine 可卡因
Both cocaine and amphetamines act primarily by increasing dopaminergic activity; cocaine inhibits dopamine reuptake, whereas amphetamine initially stimulates release of the neurotransmitter and secondarily inhibits its reuptake.

Acute intravenous administration of cocaine induces a highly pleasurable feeling (“rush”) that some individuals equate with sexual orgasm. Both cocaine and amphetamine administered before sexual intercourse are reported to facilitate orgasm and enhance the quality of this experience

Amyl Nitrite (亚硝酸异戊酯) (别名 Popper: Medicinal preparations of Amyl Nitrite are sold in small, single-use glass ampules.In order to inhale the contents, the user breaks open the ampule, producing a slight popping sound.):  一种吸入性亚硝酸类抗心绞痈药，在欧美青年中广泛作为能够快速产生欣快效应的物质而被使用。
Nicotine 尼古丁

使用这些药物用后（特别是在性活动前）能够短期内增强性能力或引起更持久(prolonged)或强烈(intense)的性体验(sexual experience)/性高潮(orgasm)/性满足(sexual satisfication)。但长期使用者有很大可能出现性功能障碍(sexual disorders)。

Depressant drugs (2 families)
* one interacting with the GABA-A receptor (stimulating an increase in GABAergic activity)
* the other acting onopiate receptors that are normally activated by endogenous (内源性) opioid neuropeptides such as enkephalins, endorphins, or dynorphin.

GABA: gamma-aminobutyric acid 氨基丁酸。中枢神经系统里重要的抑制性(inhibitory)神经递质。广泛存在于中枢神经系统(Central nervous system)30-40%的突触里。

Alcohol:
"it provokes the desire, but it takes away the performance." William Shakespeare: Macbeth, Act II, Scene III. 酒精对性的影响

Opiates
In general, they tend to inhibit sexual response. However, when the opiate heroin is rapidly administered intravenously, which produces high drug levels in the brain, a transient, intensely pleasurable sensation is produced that some individuals describe as orgasmic

This orgasm-like experience of the heroin “rush” may be produced by stimulation of the ventral tegmental area (VTA) of the brain.

PET (positron emission tomography) studies found that the ventral tegmental area was activated in men during ejaculation (Holstege et al., 2003), and fMRI (functional magnetic resonance imaging) studies showed the nucleus accumbens area to be activated in women during orgasm.

androgens 雄性激素
testosterone: 睾酮，睾丸素。主要由睾丸（testes）分泌
androstenedione (雄烯二酮，雄甾烯二酮)、dehydroepiandrosterone（脱氢表雄酮，DHEA)）等：效果较弱的雄性激素，由甲状腺（adrenal glands）等分泌
睾丸以外组织分泌的雄性激素称为 extratesticular。能够解释部分动物和人类男性去势后仍然（可能长期）保留雄性特征、行为 /  性能力、欲望的现象。
大脑某些组织也会分泌 DHEA 等，大脑分泌的这些荷尔蒙(hormones)称为 neurosteroids (神经甾体)，其作用机制与内分泌腺分泌的（endocrine and para-endocrine）激素完全不同。
antiandrogens: Drugs that reduce testosterone levels or interfere with the effects of testosterone. chemical castration,

female
estrogens 雌激素。卵巢。研究表明外源补充estrogens对女性性活动(欲望/行为/快感)几乎没有关联。
女性的卵巢和甲状腺也生产 androgens (testosterone)。补充低剂量 testosterone 可以改善女性性活动水平。但高剂量可能引起体征雄性化(virilization)副作用。 
progesterone 孕酮。卵巢、甲状腺。

From the available evidence, we are led to conclude that both men and women use a combination of androgen and estrogen, naturally resulting from testosterone metabolism, to facilitate sexual response, including orgasm.

Oxytocin
A positive correlation between the intensity of orgasm and the concentration of plasma oxytocin has been found in both sexes
Prolactin
it has been proposed that normally, the prolactin released at orgasm almost immediately “feeds back” on the brain circuits related to sexual motivation and inhibits sexual drive.
there is a report of a man capable of experiencing three orgasms without intervening postejaculatory “refractory” periods (time unresponsive to sexual stimulation) who failed to show any rise in prolactin following orgasm.

Maps of the sensory cortex show that sensation from the foot projects to the cortex immediately adjacent to the region receiving sensation from the genitals. There was a case The case of a man who described (much intenser than genitals) orgasms in his amputated phantom foot. It is likely that after amputation of the foot, fi bers of the neurons in the genital sensory cortex “invade” or “sprout” into the adjacent region, vacated by the neuron fibers that originally came from the foot