Fine structure of the Herbst corpuscles in the lingual mucosa of the finch, Lonchura striata

Tactile sensation in birds: Physiological insights from avian mechanoreceptors

The sense of touch is ubiquitous in vertebrates and relies upon the detection of mechanical forces in the skin by the tactile end-organs of low-threshold mechanoreceptors. Significant progress has been made in understanding the mechanism of tactile end-organ function using mammalian models, but the detailed mechanics of touch sensation in Meissner and Pacinian corpuscles, the principal detectors of transient touch and vibration, remain obscure. The avian homologs of these corpuscles present an opportunity for functional study of mechanosensation in these structures, due to their relative accessibility and high abundance in the bill skin of tactile-foraging waterfowl. Here, we review the current knowledge of mechanosensory end-organs in birds and highlight the utility of the avian model to understand general principles of touch detection in the glabrous skin of vertebrates.

Comparative distribution and arrangement of Herbst corpuscles in the oropharynx of the ostrich (Struthio camelus) and emu (Dromaius novaehollandiae)

Herbst corpuscles are widely distributed throughout the oropharynx of the ostrich and emu in contrast to the general situation in birds. Knowledge of the comparative distribution of Herbst corpuscles in the oropharynx of these two commercially important ratite species may assist in a better understanding of their feeding habits. Tissue sections representing all parts of the oropharynx of five ostrich and five emu heads collected after slaughter were prepared for light microscopy, the Herbst corpuscles counted, and the relative percentage of corpuscles calculated for defined anatomical regions. Herbst corpuscles were more widespread in the oropharynx of the emu (where they were additionally found in the tongue and laryngeal mound) than in the ostrich but were absent from the pharyngeal folds in both species. The results further indicated that Herbst corpuscles were strategically located to aid in the handling and transport of food. In this context, the high concentration of Herbst corpuscles in the prominent median palatine and ventral ridges in the ostrich denote these structures as sensory organs, namely the palatal and interramal organs. The presence of these sensory organs, coupled with the higher relative percentage of Herbst corpuscles located on the rostral oropharyngeal floor, indicate that the part of the oropharynx caudal to the mandibular and maxillary rostra forms an important sensory region in the ostrich. Additionally, species-specific concentrations of Herbst corpuscles within the oropharynx were identified which appear to assist in the accurate positioning of the tongue and laryngeal mound for cleaning the choana (internal nares) after swallowing.

Functional morphology of the tongue in the domestic goose (Anser anser f. domestica)

Using LM and SEM methods, the study describes microstructures in particular areas of the tongue of the goose. A thick multilayered keratinized epithelium forms the "lingual nail" and covers small and giant conical papillae, whereby the first functions as an exoskeleton of the tongue apex, and the latter are arranged along the lingual and well-developed connective tissue cores, and together with the bill lamellae are involved in cutting. The row of conical papillae on the lingual prominence prevents regurgitation of transported food. In the area of the "lingual nail" and in the anterior part of the lingual prominence, Herbst corpuscles are accumulated, which allow to recognize food position. Filiform papillae, as widely distributed between the conical papillae of the body, are responsible for filtering. They can be explained as long keratinized processes of the epithelium and are devoid of connective tissue cores. During food transport, the flattened areas of the lingual body and the lingual prominence are protected by a parakeratinized epithelium, but the root is covered by a nonkeratinized epithelium. The presence of adipose tissue in the tongue probably reduces pressure during food passage, but also promotes mucus evacuation from the lingual glands, thus facilitating food transport. An entoglossal bone with a continuation as cartilage is the stable structural basis of the tongue system.