Nerve Endings in Mammalian Skin

Abstract

SUMMARY To most authors the study of nerve terminations in mammalian skin has been an exercise in descriptive morphology. A single histological technique was usually considered adequate and presumably impeccable, for observations resulting from different techniques were not compared and the possibility of artefacts was not considered. The literature is thus excessively large and full of controversies over histological minutiae. It also contains theories concerning the organization of the nervous system which are at variance with the results of physiological observations. The work of a few authors is in striking contrast, but their observations have either been ignored or discounted. The recent discovery that nerve fibres can be seen in fresh specimens of cornea under phase‐contrast conditions has led to the development of new neuro‐histological techniques. These display nerve fibres and their terminals selectively in skin. They appear in an undistorted state and are virtually free from artefacts. The use of new techniques has shown that it is characteristic of all nerves entering mammalian skin to terminate in an arborization of fine (< 1μ in diameter), naked, axoplasmic filaments which probably end freely. Ensheathed stem fibres give rise to unencapsulated nerve endings in all skin strata, and terminals from neighbouring stem fibres overlap and interdigitate extensively. Axoplasmic filaments terminate in the cellular layers of the epidermis and in the dermis but in no specific relation to the capillaries. They are found in relation to the myoepithelial and gland cells of sweat glands, and in relation to the adventitia and media of blood vessels. In hairy skin there are in addition to the unencapsulated nerve endings nerves which end specifically in relation to hair follicles. Ensheathed myelinated stem axons give rise to two distinct and separate series of arborizations of fine, naked, axoplasmic filaments which lie at right angles one within the other. The outer series encircle the hair lying among the cells of the middle layer of the dermal coat. The inner series lie among the cells of the outer root sheath parallel to the hair shaft. No encapsulated nerve endings are seen in hairy skin. In glabrous skin and mucous membranes, such as the lip, anus and glans penis, there are, in addition to the unencapsulated nerve endings, numerous encapsulated nerve endings. They are of different sizes and shapes, and the ensheathed myelinated stem fibre or fibres which enter the capsule pursue a more or less tortuous course. They then give rise in all cases to an arborization of fine, naked, axoplasmic filaments which end freely among the capsular cells in planes roughly parallel to the surface layer of cells. In the light of these findings a re‐analysis of the observations and, in particular, the diagrams in the literature, forces one to the conclusion that the actual facts which have been reported by various authors have more in common than would have been supposed from a perusal of their summaries and conclusions. As th...

An unusual case of neuroma of the median nerve.

“…Consequently, the number of remaining normal nerve fibres is insufficient to give rise to a normal pattern of impulses which would elicit sensation. Such an explanation is in accord with the views of Weddell, Palmer, and Pallie (1955).…”

Cutaneous Heat and Cold Receptors With Slowly Conducting (C) Afferent Fibres

“…The effective stimuli caused large changes ( + 100 C.) in cutaneous temperature. Although no histological difference can be seen in the afferent plexuses in hairy skin which could account for the differential sensitivity of the nerve-endings [Weddell, Palmer and Pallie, 1955] there can be no doubt that the endings of the unmyelinated afferent axons do differ in their sensitivity to stimuli which in man give rise to distinctive sensations. Douglas and Ritchie [1957] and Douglas, Ritchie and Straub [1959] have recently been examining the responses in C fibres in the saphenous nerves of cats and have reported the absence of anv specific thermal receptors.…”

Vibrotactile sensitivity and the frequency response of the Pacinian corpuscle

“…By 1912 this foundation had been broadened to include as many as 34 separate terminations (Botezat, 1912). In a series of papers the Oxford group (Weddell, Palmer, & Pallie, 1955) brought down this edifice asserting that there was no anatomical evidence that specific end organs exist in mammalian skin.…”