THE CIRCUMCISION REFERENCE LIBRARY
Sensuality is usually discussed in terms of the central appreciation of those complex stimuli and associations that give rise to it. Much of the primary erotic stimulus comes from the skin, and a definition in terms of the sensory receptors of the skin should be a necessary part of our understanding of the physical part of this complex sensation. It is hoped that those who study human behavior will find the following anatomic and developmental information useful.
Two types of erogenous zones exist in the skin: nonspecific and specific. In the nonspecific type the skin is similar to any other portion of the usual haired skin. The nerves supplying it are composed of the usual density of dermal-nerve networks and hair-follicle networks. Examples of this type of skin are the sides and back of the neck, the axillas and the sides of the thorax. The pleasurable sensation perceived from these regions is simply an exaggerated form of tickle. The pleasant associations and the learned and anticipated responses concurrent with the stimulus produce the final amplified central sensation.
The specific type of erogenous zone found is found in the mucocutaneous regions of the body. Such specific sites of acute sensation in the body are the genital regions, including the prepuce, penis, clitoris and external vulva of the female and perianal skin, lip, nipple and conjunctiva. It is the special anatomy of these regions that require the term "specific" when one speaks of erotic sensations originating in the skin. This anatomy favors acute perception. The rete ridges of the epithelium are well formed and more of the organized nerve tissue rises higher in the dermis than is true of haired skin. The relationship between the anatomy of the skin in those structures and the nerve supply is shown in figure 1. The structures, as hair follicles, that occupy the dermis determine to some extent the neural formations. Dermal thickness also is a factor. The inverse relationship between mucocutaneous end organs and hair follicles as one moves from glabrous to haired skin should be observed.
While the innervation of these regions consists principally of dermal-nerve networks, which are present in all other skin surfaces, it is the presence of the mucocutaneous end-organ that makes special consideration necessary. My early studies of these end-organs with methylene blue and frozen silver technics have been reported elsewhere.1
The innervation of the genitalia has been described by authors as early as William Krause.2 Tello3 gave a minute and excellent description of the clitoris. Jaeger4 from studies on the penis and clitoris, concluded that a specific end-organ existed in these regions. Kantner,5 on the basis of his review of the literature, felt that no specific ending existed. I believe that a definite ending exists but that it has no specific morphology that characterizes it as a separate end organ, since it is found in other mucocutaneous regions.
Fig. 1 Diagrammatic representation of mucocutaneous transitional zone showing correlation of cutaneous anatomy with nerve structure.
There appears to be no advantage in retaining such terms as "Krause end-bulb," Endkapseln, "Dogiel body" or "genital body" for the ending seen in figure 2.
The mucocutaneous end-organs extend from the distal margin of the prepuce to the site at which hairy skin begins, where they diminish and disappear. Because of the thin dermis and minimal subcutaneous tissue in the prepuce, the nerve networks are closely set. The number of Vater-Pacini corpuscles in tissue from the adult appears to be decreased from that in tissue from the newborn. This decrease is apparently relative, however, and seems to be due to expansion of the organ rather than to diminution of the absolute number of corpuscles present. This observation indicates that Vater-Pacini corpuscles do not form after birth. In contrast, the mucocutaneous end-organs are formed in the prepuce after birth. One primitive ending was found in the prepuces of 30 newborn infants, while many well organized end-organs are present in each sample from the prepuce of the adult.6
Fig. 2 Mucocutaneous end-organ from glans penis of adult human (frozen-section silver method; X 800).
Tello3 did not find Meissner corpuscles or Ruffini end-organs in the clitoris. He noted prominent genital corpuscles, as did Jaeger.4 Tello,3 Ohmori,7 and later Yamada8 stated that the degree of organization of the genital corpuscles increases with age, even after puberty. Tello3 found a diminution of the superficial nerves and an increase in the complexity and organization of the deeper nerve endings in old age.
I have observed that the clitoris possesses the most dense nerve supply of any region of the skin, with numerous mucocutaneous end-organs and closely set networks of nerves. The Vater-Pacini corpuscle is present in the base of the clitoris. The organized mucocutaneous ending is present over the entire inner surface of the labia majora and labia minora, with a concentration toward the clitoris. The deep vaginal mucosa that has been available for investigation has not shown any specific nerve endings. No intraepithelial endings have been found.
The mucocutaneous end-organs are present over the surface of the glans penis, and especially about the coronal sulcus. The Vater-Pacini corpuscles are found in the subcutaneous tissue of the glans in their normal form. The small phallus of a hermaphrodite that I examined had a greater density of nerve tissue than the glans penis usually has. Abnormal Vater-Pacini corpuscles with an enlarged inner bulb and an unusually convoluted and divided and divided nerve expansion were found in it. A mucocutaneous end-organ from this tissue is seen in figure 3.
Fig. 3. Mucocutaneous end-organ from rudimentary phallus of a hermaphrodite (frozen-section silver method, X400).
As one moves from the hairy skin to the glabrous skin about the anus, one observes that the nerve networks rise higher and higher in the dermis and that the mucocutaneous end-organ becomes apparent at the vermillion border. These endings, as well as more non-specific papillary endings, occur frequently in this transitional zone. The Vater-Pacini corpuscle is found deep in the subcutaneous tissues of this region.
One may find varied papillary end organs in the lip. Most of them resemble rudimentary mucocutaneous end-organs and are situated in the superficial part of the dermis. Meissner corpuscles have been described by other authors, such as Ceccherelli,9 but I have not seen any specific endings of this kind in many sections of tissue from the lip. The tactile disk has been seen in the lip of the cat, but not in the human lip. The nerve networks are in close relationship to the epithelium of the vermillion border of the lip and begin to diminish in density as one approaches the haired surface of the outer part of the lip. Toward the oral cavity the dermis becomes thinner and the number of organized nerve endings diminishes. Subcutaneous tissue is absent and the network dermal nerves become more superficial. I have not found Vater-Pacini corpuscles in the structure of the lip, nor have they been reported at this site by others.
Fig. 4 Mucocutaneous end-organ from conjunctiva (reproduced from Krause, William, On the Termination of the Nerves in the Conjunctiva. (J. Anat. 1:346, 1867).
Ceccherelli10 described Ruffini and Meissner corpuscles together with different kinds of varicose expansions of nerves in the mucosa of the tongue. Botezat11,12 described complicated papillary endings in the oral cavity of man and other mammals Gairns and Aitchison13 found that the nerve endings in the human gum varied widely in form. Gairns14 found similar endings in all types of papillae of the tongue. Many of his illustrations are entirely comparable to my illustrations of mucocutaneous end-organs.
One may find special mucocutaneous endings in the thin zone of transitional glabrous skin. These are in the papillae. None have been found in the conjunctiva. Krause described the human end-bulb in the conjunctiva proper as shown in figure 4. Strughold and Karbe15 and Sakamoto16 described an ending in this location which appears to represented nerve-trunk artifacts. Recent work of Oppenheimer, Palmer, and Weddell17 confirms my conclusion that most of the nerves in his region end as free arborizations.
Martynoff18 found Golgi-Mazzoni, Vater-Pacini and genital corpuscles in the areola and nipple. Belonoschkin19 observed what he termed a "Krause end-bulb in the areola and nipple. Cathcart and colleagues20 did not confirm these findings. They found no Meissner corpuscles and few organized endings of any nature. I have found the dermal-nerve networks and the concentrations of nerve tissue about ducts and along masses of smooth muscle. The presence of hair in the areola itself gives rise to some additional sensory tissue. It is apparent that the mass of smooth muscle and glandular-duct tissue in the nipple and areola serves to block normal development of the dermal-nerve networks seen in other erogenous regions. The nipple is well innervated immediately below the epidermis, but the glandular and smooth-muscle structures crowd out the uniform richness of middle dermal networks and prevent development of special end organs.
This is elongated and sometimes serpentine nerve receptor composed on a central axial nerve and closely set, non-expanded, concentric fibrillar lamellae (fig. 5). It is found in the mucocutaneous regions of lower mammals, such as the dog, cat, cow, mole, guinea pig and rat.21,22 It is found in the paw or hoof of these animals. In addition, it is found in the nose of the pocket gopher and the mole. It appears to be a general biologic phenomenon in mammals. It is nonspecific cholinesterase-positive in all species of mammals tested, and alkaline phosphatase-positive in some of these. Its resemblance to the isolated inner bulb of the Vater-Pacini corpuscle is so close as to require no attention.
A great unity exists in the forms of innervation of the several true erogenous zones in any animal. In primates the ending appears to be principally nonmyelinated nerve, while in the lower animals the ending is convoluted and heavily encapulated. The single exception of the nipple region is adequately explained by the anatomy of that region. Compared with lower animals, the primate group is much better equipped to appreciate sensations in special tactile zones such as the hand, as well as in the erogenous zones.
Fig. 5. Mammalian end-organ in hoof of calf (frozen-section silver method; X325).
These end-organs develop principally after fetal life. No adequate knowledge of true relations exists, but it is apparent that most significant morphological changes occur after several or many years of organized extrauterine life. This would fit well with the basic psychiatric concept of oral, anal, and genital eras in man's psychic development. We do not know that such a progressive morphological organization of cutaneous nerves occurs but in view of the organized behavior patterns, it would be logical to look for it. Much behavior is readily explicable on the basis of an identity of the oral, anal, and genital regions in regard to nerve supply. It is now confirmed that such a peripheral sensory identity does exist.
All biologic phenomena, including sensation, are the result of a certain statistical events. It is logical to anticipate that some individuals will have cutaneous hyperneuria, and also to expect eventually to find some individuals with actual diminution in organization of the cutaneous nerves for sensation. Certain pathologic states may be explicable on the basis of diminished or augmented cutaneous nerve supply. Examples of these might be satyriasis, priapism, nymphomania, impotence and frigidity. It is entirely possible that glossopyrosis is related to degenerative changes accompanying ageing of the oral tissues. Since adequate data are not available on these subjects, one can only speculate that an anatomic basis for these various clinical syndromes may some day be found. This would not diminish the tremendous importance of psychiatric contributions to these subjects but would serve to make definition of the psychosexual states clearer.
There are two types of erogenous zones: nonspecific and specific. Those of the nonspecific type depend upon exaggeration of a basic tickle sensation. Specific erogenous zones, the mucocutaneous zones of man and animal, have special neural and cutaneous anatomic characteristics. The mucocutaneous end-organs in any given species appear to be identical in all of the the zones. The endings of the primates are markedly different from those of lower animals. Development of the nerve endings is principally postfetal and may coincide with the organization of oral, anal and genital patterns of behavior.
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