The sensory innervation of primate facial skin. II. Vermilion border and mucosa of lip
Abstract
The innervation of the vermilion border and mucosa of the monkey lip have been studied by light and election microscopy. Meissner corpuscles are present at the junction between hairy skin and vermilion border usually high in the dermal papillae, tightly abutting the overlying basal layer of the keratinized squamous epithelium. These Meissner corpuscles resemble those described in primate glabrous skin and are characterized by the presence of stacks of lamellae interposed between loops of the terminal axon. The lamellae are cytoplasmic extensions of specialized Schwann cells referred to as lamellar cells. One to three myelinated axons, 2–4 μm in diameter, innervate a single Meissner corpuscle.
Coiled simple corpuscles, innervated by 1–3 myelinated axons, 3–5 μm in diameter, are characteristic of the non-keratinized portion of vermilion border and oral mucosa. The terminal axons in simple corpuscles are enveloped by circumferentially arranged cytoplasmic lamellae. Small terminal axoplasmic spikes protrude into spaces between the cytoplasmic lamellae in both Meissner and simple corpuscles. Cytoplasmic lamellae in both receptors are characterized by the presence of numerous pinocytotic vesicles. The lower parts of Meissner as well as simple corpuscles are encapsulated by perineurium and these perineural epithelial cells have incomplete basal lamina on both sides of their flattened cytoplasm. In contrast, corpuscles that are present high in the dermal papillae have scant perineural capsular elements and instead have fibroblast-like cells demarcating the inner core of the corpuscle from the general connective tissue compartment. Endoneural fibroblasts are a constant component of all corpuscular receptors. Tactoids of fibrous long-spacing collagen are present in the endoneural connective tissue of these sensory corpuscles. The vermilion border has 10–20 corpuscular receptors per mm2 of surface area. Tastscheiben consisting of clusters of Merkel cells and their associated axons are present in the basal layer of rete ridges and rete pegs throughout the hair skin, vermilion border, and oral mucosa of the primate lip.
Free nerve endings (FNE's) have been identified using cytologie criteria described previously54. FNE's in the vermilion border and mucosa often establish intimate contact with the basal lamina and/or basal cells of the epithelium. FNE's can also be identified in dermal papillae that contain Meissner and/or simple corpuscles. Ruffini nerve endings are not present in dermal papillae. This relatively dense sensory innervation can be correlated with the known tactile sensitivity of the lip in terms of twopoint as well as force thresholds and expanded areas of thalamic and cortical representation.
The innervation of glabrous skin resembles that of hairy skin with Meissner and simple corpuscles of glabrous skin being equivalent to lanceolate terminals of hairy skin. The other sensory terminals of each type of skin are identical. Hairs provide an anatomical substrate for multiple afferent terminals, and rete ridges/dermal papillae are the equivalent structural unit in glabrous skin. Each cutaneous anatomical site can be multiply innervated, and this afferent information is processed centrally over multiple parallel ascending systems.
Coiled simple corpuscles, innervated by 1–3 myelinated axons, 3–5 μm in diameter, are characteristic of the non-keratinized portion of vermilion border and oral mucosa. The terminal axons in simple corpuscles are enveloped by circumferentially arranged cytoplasmic lamellae. Small terminal axoplasmic spikes protrude into spaces between the cytoplasmic lamellae in both Meissner and simple corpuscles. Cytoplasmic lamellae in both receptors are characterized by the presence of numerous pinocytotic vesicles. The lower parts of Meissner as well as simple corpuscles are encapsulated by perineurium and these perineural epithelial cells have incomplete basal lamina on both sides of their flattened cytoplasm. In contrast, corpuscles that are present high in the dermal papillae have scant perineural capsular elements and instead have fibroblast-like cells demarcating the inner core of the corpuscle from the general connective tissue compartment. Endoneural fibroblasts are a constant component of all corpuscular receptors. Tactoids of fibrous long-spacing collagen are present in the endoneural connective tissue of these sensory corpuscles. The vermilion border has 10–20 corpuscular receptors per mm2 of surface area. Tastscheiben consisting of clusters of Merkel cells and their associated axons are present in the basal layer of rete ridges and rete pegs throughout the hair skin, vermilion border, and oral mucosa of the primate lip.
Free nerve endings (FNE's) have been identified using cytologie criteria described previously54. FNE's in the vermilion border and mucosa often establish intimate contact with the basal lamina and/or basal cells of the epithelium. FNE's can also be identified in dermal papillae that contain Meissner and/or simple corpuscles. Ruffini nerve endings are not present in dermal papillae. This relatively dense sensory innervation can be correlated with the known tactile sensitivity of the lip in terms of twopoint as well as force thresholds and expanded areas of thalamic and cortical representation.
The innervation of glabrous skin resembles that of hairy skin with Meissner and simple corpuscles of glabrous skin being equivalent to lanceolate terminals of hairy skin. The other sensory terminals of each type of skin are identical. Hairs provide an anatomical substrate for multiple afferent terminals, and rete ridges/dermal papillae are the equivalent structural unit in glabrous skin. Each cutaneous anatomical site can be multiply innervated, and this afferent information is processed centrally over multiple parallel ascending systems.
Bibliographical data
| Original language | English |
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| Article number | 1 |
| ISSN | 0006-8993 |
| DOIs | |
| Publication status | Published - 1983 |
| pubmed | 6824957 |
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