Structure of the Sensory Innervation of the Anal Canal in the Pig

Abstract

The sensory innervation of the anal canal of the pig was investigated by light and electron microscopy. The distribution of the different types of sensory nerve endings correlates with the histology of different zones: (1) After the rectal mucosa there was a zone lined with nonkeratinized stratified squamous epithelium. (2) A middle zone was lined with keratinized stratified squamous epithelium. Here the dermis already showed a papillary and a reticular layer. (3) The last zone showed hairy skin with a high hair density. The following nerve endings were found: Free nerve endings reached the stratum superficiale in nonkeratinized squamous epithelium and the stratum granulosum in the keratinized squamous epithelium. Dermal free nerve endings were found in all zones near the epithelium and two different types were identified as those derived from C-fibers and those from A-delta-fibers. Merkel nerve endings showed different features depending on their location. Few Merkel-like cells were found in the epithelium of the anal crypts. Typical Merkel ‘Tastscheiben” were located at the base of epithelial ridges or pegs in zones 2 and 3. The number of Merkel cells varied up to 200. The myelinated afferent fiber supplied 10–15 Merkel cells. Merkel cells were also found regularly in the outermost layer of the external rooth sheath of hair follicles at about the same level as perifollicular nerve endings. Lamellated corpuscles were found in the dermis of all zones except the cranial part of zone 1, where the anal crypts are located. Generally they consisted of a central nerve terminal which may be branched. Each terminal was surrounded by an inner core of concentrically arranged lamellae of the terminal Schwann cell and one or several inner cores were included in a capsule of perineural cells. The size of the corpuscle, the regularity of the inner core and the number of capsular layers depended on the location of the corpuscle. The closer it was to the epithelium, the less well developed was the capsule and the smaller the corpuscle tended to be. Perifollicular nerve endings andpilo-Ruffinicomplex are unique features of the sensory innervation of hairy skin. They were regularly found with the large guard hairs.

Pudendal afferent innervation of the guinea pig external anal sphincter

“…The responses of the rapidly adapting afferents in this study were more consistent with cutaneous pacinian corpuscles that respond to force with an all‐or‐none response 19 . Pacinian‐like corpuscles have been documented in the anal mucosa of human and pig, 27,28 but in our preparations both submucosa and mucosa had been removed leaving only muscle. Rapidly adapting afferents are absent from skeletal muscle 19,29 .…”

Intercellular junctions between palisade nerve endings and outer root sheath cells of rat vellus hairs

“…We demonstrated intercellular junctions between the PN and ORS, although most previous ultrastructural studies described the PN external to the basal lamina of the ORS (Andres, 1966;Yamamoto, 1966;Orfanos, 1967;Cauna, 1969;Munger, 1971;Hashimoto, 1973;Halata, 1975Halata, , 1978Halata and Munger, 1980;Munger and Halata, 1983;Retting and Halata, 1990). Hashimoto (1973) reported that the lanugo hairs of the human face rarely had direct contact with a receptor organ via the ORS cell without the interposition of the basal lamina.…”

“…They ascend along the long axis of the hair follicle (Cauna, 1959(Cauna, , 1969Halata, 1978;Halata and Munger, 1980;Munger, 1982;Munger and Halata, 1983;Rice and Munger, 1986;Millard and Woolf, 1988;Munger and Ide, 1988;Retting and Halata, 1990;Fundin et al, 1997a) and perceive deformation of the hair (Hashimoto, 1973;Cauna, 1976). Previous electron microscopic studies of the PN provided common ultrastructural images of the PN as follows: Each sensory nerve ending is sandwiched between two layers of Schwann cell processes, forming a unit.…”

“…Previous electron microscopic studies of the PN provided common ultrastructural images of the PN as follows: Each sensory nerve ending is sandwiched between two layers of Schwann cell processes, forming a unit. The nerve endings, as well as the Schwann cell processes, of the PN are always found lying outside within a short distance of or directly abutting on the basal lamina of the outer root sheath (ORS) cells (Yamamoto, 1966;Andres, 1966;Orfanos, 1967;Cauna, 1969;Munger, 1971;Hashimoto, 1973;Halata, 1975Halata, , 1978Halata and Munger, 1980;Munger and Halata, 1983;Retting and Halata, 1990). Direct intercellular relationships between the PN and ORS were not shown by these authors, except for Hashimoto (1973).…”

Sensory nerve formations in the skin and their classification

“…It consists of 10-20 Merkel complexes (Iggo and Muir, 1969). At the base of epithelial ridges of the pig anal canal, Rettig and Halata (1990) ata, 1972a,b). Also Gottschaldt (1985) places the Eimer's organ of the mole into the group of complex sensory structures.…”