Vincent Di Marino1 and Hubert Lepidi1
(1)
UER Médecine, Aix-Marseille Université, Marseille, France
Abstract
Although our study is mainly anatomical, it appeared useful to include some physiological data specifically related to the modifications and the role of the bulbo-clitoral organ during the different phases of the sexual act.
15.1 General
Although our study is mainly anatomical, it appeared useful to include some physiological data specifically related to the modifications and the role of the bulbo-clitoral organ during the different phases of the sexual act.
How does this organ behave during intercourse? Here is a question, which has remained without an accurate answer for a long time, as if it were taboo or too mysterious to be mentioned. Fortunately, what was, up until now, only assumptions or the product of people’s imaginations has now been confronted with the reality of images obtained with various methods of exploration and especially techniques providing dynamic representations. The recent progress made in studies on intercourse in relation to computed tomography, NMR (publications of A. Burdens et al.), echography (work of Odile Buisson and Pierre Foldes), macrophotography and videos have finally made it possible to clarify this question.
15.1.1 Description of the Different Phases
It should be recalled that, since the work of W.H. Masters and V.C. Johnson, it is known that the sexual cycle of a woman, when it is complete (and therefore ideal!), has four phases: an excitation phase of variable duration, a plateau phase (which lasts for 3 min maximum), an orgasm phase (which only lasts a few seconds1) and a resolution phase of 15 min.
During the phase of sexual excitation, triggered by the imagination and erotic memories, a favourable context, the stimulation of various erogenous areas in a woman (including the clitoris itself) and maintained through the secretion of dopamine,2 the bulbo-clitoral organ undergoes many significant transformations:
· Due to the blood supply to the erectile bodies, the latter will increase in volume with the intumescence of the entire bulbo-clitoral organ, at the level of the spongy bodies (which explains the rising of the labia minora) as well as at that of the cavernous bodies, until the erection of the clitoris. Such as already observed, in the chapter devoted to the physiology of the cavernous and spongy tissues, this erection, although real (rigidity and extension of the body of the clitoris), will remain with a limited amplitude, resulting in a slight rising of the descending portion of the clitoris (increase in the angular opening of the clitoral elbow, in a sagittal plane) and a potential extrusion of the glans outside the hood.
· At the same time, vasodilatation will diffuse to all the vascular networks communicating with the erectile bodies. We will therefore observe significant effects on all of the external genitalia, including, in particular, the swelling of the labia minora, but also on the urethra and the vagina (congestion of the urethral and vaginal vessels). This vaginal hyperhemia will result in an increase of the capillary pressure and an important transudation (high concentration in Na+ and Cl− ions) in the vaginal lumen. This transudation is, furthermore, favoured by an increase in capillary permeability, which, itself, is under the influence of neuromediators such as the VIP. This transudate becomes so significant that the capacity of reabsorption through the vaginal epithelium is saturated (R.J. Levin), which produces and maintains the vaginal lubrication essential for the copulation. Many secretions also contribute to this phenomenon: secretions of the glands of the uterine collar, of the vestibular glands (grater vestibular glands, in particular) and of Skene’s paraurethral glands.3 The entire lubrication process is under hormonal influence (essential role of the oestrogens4).
The penetration and the back-and-forth movements of the male penis in the vestibulo-vaginal tract will then generate, in women, various phenomena leading to the full completion of the sexual act. These phenomena will enable her to reach the plateau phase. We will successively consider the following:
· The penetration and the vagino-cavernous reflex
· The penetration and the movements of the deep bulbo-clitoral structures
· The stimulation of the external clitoris
· The stimulation of the urethra
· The contraction of the levator muscles
· The vagino-cavernous reflex is triggered by vaginal distension caused by the penetration. This distension generates the reflex contraction of the ischiocavernous and bulbospongious muscles. The EMG studies showed that this reflex occurs during each penetration movement and that the amplitude of the muscular contraction potentials is proportional to the significance of the vaginal distension (work completed by A. Shafik with small inflated air small balloons with progressive volumes). This reflex plays an essential part for the two partners, as it contributes to maintaining the erection of the clitoris (by compressing the veins of the clitoris via the strap of the bulbospongious muscles and by compressing the erectile bodies via the action of the ischiocavernous and bulbospongious muscles) as well as the erection of the penis (compression of the dorsal vein of the penis and of the penile erectile bodies by the contracted bulbospongious muscles, erotic stimulation of the penis through the contraction sensation of the partner’s peri-vaginal muscles5) and the quantity of sperm (according to A. Shafik, the vagino-cavernous reflex increases the volume of ejaculate while expulsing, towards the vagina, the residual sperm remaining in the urethral lumen of the urethral tract).
· The penetration will displace the deep structures of the bulbo-clitoral organ to a certain degree. The penis in erection (thus dilated and rigid) penetrates the vagina (thickened through vasodilatation) according to a boomerang-type trajectory6 regardless of the position of the partners.
During this penetration, it will push the anterior vaginal wall backwards and the urethra forwards, by applying, with a certain force, these structures on the commissure of the bulbs and on the intermediate area, which will be crushed against the pubic symphysis (Fig. 15.1). Similarly, the penis drives back the lateral walls of the vagina, thus compressing not only the bulbs but also the clitoral roots, which are all at maximum turgescence.
Fig. 15.1
Sketch from a coronal section of the erectile bodies during coïtus, at the time of the penis pressure (note: white captions for bulbo-clitoral organ; blue captions for penis). White captions: a albuginea (getting very thin because of the turgescence of corpora cavernosa), b bulb, CC corpus cavernosum, cr crus clitoridis, m1 ischiocavernosus muscle, m2 bulbo-spongiosus muscle, U female urethra, right white arrow location of the pars intermedia, curved white arrow commissure of the bulbs (commissura bulborum). Blue captions: aalbuginea, b corpus spongiosum urethrae (spongiosus bulb), CC corpus cavernosum, U male urethra (penile urethra), V subcutaneous dorsal vein, V′ deep dorsal vein, right blue arrowit shows the Buck’s fascia (fascia penis), Blue arrowhead they show the erected penis. Other captions: P pubic symphysis, i-p r ischio-pubic ramus, ctp central tendon of perineum, little pink arrows they show the posterior part of the vaginal wall (the vaginal cavity is completely distended by the penetration of the erected penis)
With an echography (work performed by O. Buisson et al.), it is possible to observe, during each penetration, an actual “displacement” of the bulbo-clitoridal organ. The arc formed by the commissure of the bulbs increases in size, while the bulbs, which are saturated with blood to their maximum capacity, become wider. The roots of the clitoris, whose volume doubles during the back-and-forth movements, are drawn apart by the dilated penile cylinder. Their junction angle is transformed into an arc. The intermediate network is also pushed back against the symphysis. Each back-and-forth movement acts as a pump and propels blood to the clitoral body through the vessels of this network.7 Overall, during the penetration-withdrawal movements, the internal part of the female erectile bodies is the site of maximum blood saturation and intense compressive phenomena, which tend to make the blood flow back to the discharge pathways (Kobelt’s network and peri-vaginal venous plexus). It obviously generates an intense stimulation of the anterior vaginal wall and of the urethra, which are caught in a vice-like grip between the female erectile bodies and the penis at maximum turgescence.
In men, the combination of vascular saturation, which induces the erection, and of the compressive phenomena generated by the turgescence of the female erectile bodies similarly maintains the stimulation and thus the erection.
There is thus a true feedback, “a sexual synergy of the two partners with reciprocally reinforced phenomena” (P. Lavoisier et al.). The penis in erection, penetrating the vagina, modifies the intra-vaginal pressure and generates the tumescence of the erectile bodies and the erection of the clitoris. At the same time, the congestion of the peri-vaginal vessels compresses the vagina and thus the penile cylinder increases the intra-cavernous pressures of the penis and maintains its erection.
The back-and-forth movements will enable the following:
· The bulbo-clitoral organ will be able to expand during each partial withdrawal.
· The vagina will be able to vary the pressures applied to its wall by increasing them with each withdrawal movement of the penis, with a positive action for the tumescence of the penis when it advances again inside the vaginal cylinder.
· The penis will not undergo anoxia and will alternate phases of “external compression” (infra-systolic phases) and of “internal compression” (supra-systolic phases).8
· The stimulation of the external part, i.e. the visible part of the clitoris, is achieved by the back-and-forth movements of the penis. This stimulation is double: direct and ancillary and indirect and yet essential:
1.
2.
· Many authors also consider, and rightly so, that vaginal stimulation and clitoral stimulation are closely related to a certain degree of stimulation of the urethra. This is not surprising when we consider what anatomy teaches us:
· Communication and vascular balancing between the spongy bulbs and the peripheral plexuses of the urethral tract
· Rich innervation of the urethral wall, in particular at the level of the posterior part of the urethral cylinder, in contact with the anterior wall of the vagina
· Joining of the urethral and anterior vaginal walls, superimposed from back to front
Thus, certain authors (G. Vanneuville et al.) located the famous G spot12 at the level of the urethral sphincter. Other authors (J.L. Sevelly in particular) consider that the clitoris is not the single excitable organ during sexual intercourse and that the external ostium of the female urethra and the epithelium, which surrounds it, play an equivalently significant role. They believe that this area has a high erotic sensitivity,13 comparable to that of the end of the male glans, around the external ostium of the urethra. Sevelly called it the “female glans” (in order to not mix it up with the glans clitoridis). Still according to this author and with the support of evidence, this “female glans” is particularly excited during back-and-forth movements, as the penis always encounters it during the transition between the partial withdrawal phase and the complete insertion phase and vice versa.
Fig. 15.2
A urethral hypothesis on G point. The red circle and red arrow show the most innervated area. PS100 staining showing the innervations of the erectile bodies and of the “urethro-vaginal unit”. (a) Photomicrograph of a transverse section of the “urethro-vaginal unit”, through the crura clitoridis (the section is perpendicular to the urethral axis). (b) Magnification of the “urethro-vaginal unit” to show the rich innervation of the posterior half of the urethra above the anterior vaginal wall (red arrow). (c, d) Two microscopic aspects of the red-circled area. The multiple dark brown spots are nerves! b bulb, CC corpora cavernosa, cr crus clitoridis, CS corpus spongiosum, e left lateral edge of vagina, U urethra, Va vagina, vaanterior vaginal wall
In any case, all the authors agree to include, in the same erogenous groups, all anatomically connected organs, likely to be stimulated and excited during a sexual act. This leads to terminologies, which resemble and complete each other:
O’ Connell: clitoral complex (clitoral complex), O. Buisson: clito-urethro-vaginal complex (CUV), L.C. Lenck: urethro-clitorido-vulvar entity and, for us, the bulbo-clitoral organ and the urethro-vaginal unit.
· The roles of the pubo-rectal bundles of the levator ani muscles are better known, since the current study of these muscles by dynamic NMR, in genital cases of prolapse.14 Their voluntary and powerful contraction modifies the diameter of the urogenital hiatus. They can thus, during the penetration, reinforce the action of the ischio- and bulbocavernous muscles. Expert women, who know their body well, can thus add an additional degree of eroticisation for their partner by repeatedly contracting these pubo-rectal bundles,15 which will compress the penis in full back-and-forth action.
At the end of the plateau phase, at the maximum of the excitation phase,16 the orgasm phase will occur, when the conditions are favourable, with many simultaneous manifestations, including first and foremost, a reduction of the lumen of the lower third of the vagina, which is saturated with blood; turgescence and a modification of the colour of the labia minora; vaginal lubrication of maximum intensity; spasmodic contractions of the uterus, vagina, perineal muscles and of all the pelvic muscles17; and lastly, a temporary retraction of the clitoris in erection under the prepuce. Many vegetative reactions of the entire body (hyperventilation, arterial hypertension, tachycardia,18 redness of the face and torso, mydriasis) as well as corporal modifications (increase in the volume of the breasts with erection of the nipples) accompany these pelvic phenomena. It seems that the sensation of intense pleasure, characteristic of this highlight, is related to the rapid discharge of blood, which congested all the venous plexuses and all the pelvic tissues, under the effect of the waves of reflex contractions of the perineal striated muscles, of the levator ani muscles, of the urethral and anal sphincters and of the smooth muscle fibres of the uterus.19 The orgasm is a complex phenomenon that physiologists have greatly studied and which can be clarified by the use of modern exploration techniques.20
We should also note the significance of the neurosecretions21 occurring at this stage, especially endorphin secretions, which explain the absence of suffering and even the actual analgesia, from which women benefit during an orgasmic phase, in spite of the multiple muscular contractions and the various pressures, which are more or less violent.
The male ejaculation (which usually corresponds to the phase of male orgasm) often does not correspond to the female orgasm phase. If he can, the man must continue, as much as possible, with the rhythmic movements to prolong the sexual excitation of the woman. However, this is only possible for a short moment. When his erection ceases, the penis tends to exit the vaginal tract. But there again, the woman’s stimulation can be continued through the man’s pelvic movements, thus applying pressure on the pubis and frictions of the still turgescent penis against the clitoris, which is still in erection. In positions known as “straddle positions”, the woman has a more active role and she will have the initiative of these movements. By undulating her pelvis, she will know how to stimulate her clitoris against the root of the penis and the male pubis. This is a good way for her to reach orgasm.
The resolution phase, which occurs after the short but very intense phase of pleasure and exaltation, characteristic of an orgasm, is a phase of well-being and physical relaxation due to the pelvic-perineal vascular and muscular systems returning to their normal status. The clitoris, which was retracted under the prepuce, will return to its normal position in a few moments. However, the glans remains hypersensitive during several minutes. As for the detumescence of the body of the clitoris, it only occurs after a longer period, often exceeding 15 min. Similarly to the genitalia, the torso and the face recover their usual aspect within 10–20 min.
If no orgasm has occurred (which does not mean that there was no pleasure!), the resolution phase is shorter and lasts only around 10 min. It should be noted that a woman can also have several successive orgasms (specificity of mankind!).
15.1.2 Sexual Intercourse and Sexual Act
The significance of the bulbo-clitoral organ (whether its “internal part” or its “external part”) during the various phases of the sexual act is undeniable. However, for mankind, who is provided with an extraordinary nervous system and, especially, an exceptional brain (the most developed brain in the animal world), the sexual act cannot be compared to or mixed up with a perfect succession of mechanical phenomena, nor even with the mating of animals, with an exclusively reproductive purpose.22 The human sexual act is specific because it does not obey a simple impulse and it can be controlled by will or reason. Moreover, for humans, this act is part of an intimate context of communication: sexual intercourse. When the understanding between two partners is harmonious, this relationship will lead to an impassioned sexual act, in which each partner will not only attempt to satisfy his/her own pleasure but also that of the other. It is the brains of the two partners which will choose the most adapted words, the softest caresses and the most pleasant positions so that the union of their bodies is perfect and provides mutual and total satisfaction. At best, when the relationship benefits from a strong psycho-emotional component and that it is the expression of deep love with a wish of procreation, the conditions of the sexual act become ideal: no inhibiting cerebral factor is an obstacle, the hypothalamic endocrine secretions occur freely and dopamine, the hormone of the pleasure, is distributed abundantly. The sexual act becomes the most beautiful exchange, combining tenderness and passion, as the aim of each lover is to reach, together, the height of pleasure and exaltation, i.e. orgasm. The latter will be an “ecstatic” moment23 where the intensity of pleasure and happiness will generally be combined with a brief moment of psychic disconnection with a decreased vigilance. This phase is so complex, especially in women, that the majority of them describe orgasm like an “indefinable” state….due to the fact that when it occurs, most of the cerebral areas are activated and several neurotransmitters are involved.
The resolution phase, which will follow these moments of great intensity, will also be controlled by the endocrine system and will be readily extended, for the two lovers, by a restorative sleep.
Footnotes
1
The duration of the female orgasm (average 20 s) is greater than that of man (average 6 s)!
2
This neurotransmitter is regarded as the true “hormone of pleasure” (J.D. Vincent).
3
The excreting canals of the two paraurethral glands or glands of Skene are located on the distal end of the urethra, on either side of the external ostium of the urethra. In certain women, known as “fountain women”, during the sexual excitation phase, the secretion of these glands can be particularly abundant.
4
Vaginal dryness, a frequent occurrence after the menopause, is related to a hypo-oestrogenia. This phenomenon can also be observed in non-menopaused women, in relation to “dry syndromes” or during certain vulvo-vaginal mycoses. There are also other types of dryness of iatrogenic origin, following the absorption of certain drugs.
5
It should be recalled that the medial part of the bulbospongious muscle in a woman forms what previous scientists referred to as the “constrictor cunni”.
6
The first NMR of sexual intercourse, performed in 1999 by W.W. Schultz et al., showed that the penis in erection is, on the sagittal sections, neither straight, such as represented by Leonard de Vinci, nor shaped like an S, such as represented by R.L. Dickinson in 1933, but shaped like a boomerang as it forms a 120° angle with each of its roots.
7
Georg Ludwig Kobelt (1851), in his remarkable book, referred to the “expulsive contractions of the bulbo-spongiosus muscles” which make the blood of the bulbs flow back to the intermediate network and behave like a genuine “hydraulic apparatus (sexual heart)”!
8
The NMR images (A. Faix et al., W.W Schultz et al.) showed that during intercourse the penile glans reaches the anterior vaginal fornix or the posterior vaginal fornix and that this depends on the penetration position and on the topography of the uterus (ante- or retroverted).
9
We can very logically wonder whether the finality of clitoral erection, at a simple mechanical level, is not to prevent the clitoris from hindering or being an obstacle to penile penetration.
10
It is this dynamic (hood towards the rear and clitoral body towards the front), which partly explains the apparent temporary retractions of the glans under the hood, observable during the back-and-forth movements. These withdrawals also occur during orgasm when the muscular contractions of the ischio- and bulbocavernous muscles amplify the phenomenon.
11
A. Ingelman-Sundberg was able to systematically highlight these ligaments during operations relating to the anterior perineum.
12
The G spot (Grafenberg spot) is an area (which has still not been determined from an anatomical viewpoint) located on the anterior wall of the vagina, approximately a few centimetres from its external ostium and whose characteristic is to be extremely erogenous.
13
It should be noted that our research showed a significant amount of nerves at the periphery of the external ostium of the female urethra, but on the other hand, a total absence of corpuscles of pleasure (Fig. 15.2).
14
The usual function of the pubo-rectal bundles of the levator ani muscle is a lifting function: their contraction brings the median pelvic organs of the pubic symphysis closer together.
15
The exceptional penis captivus (involuntary muscular spasm, retaining the penis in erection inside the vagina) is due to the peri-vaginal muscles (constrictor cunni) and not to the pubo-rectal bundles of the levator ani muscles.
16
It is at the level of the limbic lobe that the pleasure sensation ends but functional MRI has shown that many areas of the brain are involved: amygdaloid body, hippocampus, accumbens nucleus, lateral hypothalamus, temporal cortex, frontal cortex with, when approaching orgasm, the production of oxytocin, which explains the small mammary discharges of this phase and the occurrence of uterine contractions.
17
These muscle contractions occur in two phases: the first, unique and intense, the tonic phase, the second, made of short burst contractions, the clonic phase (suggestive of clonic seizure).
18
A respiration rate of 30/min, a systolic blood pressure of 20 and a pulse of 120 are not exceptional.
19
The rhythmic contractions of the uterine musculature are controlled by the vegetative system (utero-vaginal plexus).
20
Cerebral NMR (B. Komisaruk 2011) has shown that, during orgasm, most of the cerebral zones are activated.
21
The most important neurosecretions during the orgasmic phase are the dopamine, the oxytocin and the
endogenous opioids.
22
However, certain specialists of the animal world consider that female cats and apes can have orgasms.
23
Certain authors think that the exaltation and the impression of detachment of the body, felt by hundreds women during orgasm, share common features with the ecstasy phenomena observed in great mystics.