The sensory innervation of primate eyelid

Abstract

The skin of primate eyelid contains three distinctive sensory nerve terminals. Small down hairs have a collar of lanceolate terminals that are formed by ramifications of the six to eight myelinated afferent fibers. Extensions of Schwann-cell cytoplasm form masses of cytoplasmic lamellae associated with these terminals. Every large hair or eyelash contains a large pilo-Ruffini as well as sparse lanceolate terminals. The eyelash Ruffini corpuscle resembles those of monkey facial guard hairs, sinus hairs, and joint capsules of the cat and pigeon. Sparse lanceolate terminals present between the Ruffini corpuscle and eyelash external root sheath resemble those of vellus hairs. On rare occasion Merkel cells are present in the hair follicle external root sheath above the sebaceous gland. Merkel touch spots, or Tastscheiben, are located between contiguous eyelashes as small rete pegs containing several Merkel cell-neurite complexes innervated by one or two myelinated afferent fibers. The function of this array of sensory terminals is presumed to represent an extensive mechanism of protection for the cornea and globe. On the basis of studies reported to date we can conclude that the Ruffini corpuscles (and related receptors) are the ubiquitous mechanoreceptors of cutaneous and musculoskeletal systems in birds as well as mammals.

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).…”

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

“…Their structure resembles the so-called pilo-Ruffini complex [Biemesderferct al.. 1979: Halata and Munger. 1980a, b: Munger and Halata.…”

Blink-related sensorimotor anatomy in the rat

“…The primate eyelid is densely innervated by lanceolate terminals on vellus hairs, piloRuffini complexes and lanceolate terminals on eyelashes and Merkel touch spots in the epidermis (Halata and Munger 1980). These sensory nerve terminals are extensions of myelinated axons.…”