The anatomy, function, and development of mammalian Aβ low-threshold mechanoreceptors

Abstract

Touch sensation is critical for our social and environmental interactions. In mammals, most discriminative light touch sensation is mediated by the Aβ low-threshold mechanoreceptors. Cell bodies of Aβ low-threshold mechanoreceptors are located in the dorsal root ganglia and trigeminal ganglia, which extend a central projection innervating the spinal cord and brain stem and a peripheral projection innervating the specialized mechanosensory end organs. These specialized mechanosensory end organs include Meissner's corpuscles, Pacinian corpuscles, lanceolate endings, Merkel cells, and Ruffini corpuscles. The morphologies and physiological properties of these mechanosensory end organs and their innervating neurons have been investigated for over a century. In addition, recent advances in mouse genetics have enabled the identification of molecular mechanisms underlying the development of Aβ low-threshold mechanoreceptors, which highlight the crucial roles of neurotrophic factor signaling and transcription factor activity in this process. Here, we will review the anatomy, physiological properties, and development of mammalian low-threshold Aβ mechanoreceptors.

Keywords: Meissner’s corpuscle; Merkel cell; Pacinian corpuscle; Ruffini corpuscle; dorsal root ganglion; lanceolate ending; mechanoreceptor.

Figure 1

Illustration to demonstrate the morphologies and physiological properties of mammalian Aβ low-threshold mechanoreceptors. In glabrous skin (left side of the illustration), Meissner’s corpuscles are located in the dermal papillae of the dermis, Merkel cells are located in the basal epidermis, Ruffini corpuscles are located in the dermis, and Pacinian corpuscles are located in the dermis, deeper than the other mechanosensory end organs. In hairy skin (right side of the illustration), hair follicles are surrounded by lanceolate endings and Merkel cells. The bottom panel shows the neural activity of different types of Aβ low-threshold mechanoreceptors in response to a sustained stimulus. Meissner’s corpuscle, Pacinian corpuscle and lanceolate ending mechanoreceptors display rapidly adapting mechanosensitive physiological properties, while Merkel cell and Ruffini corpuscle mechanoreceptors display slowly adapting mechanosensitive properties, which fire action potentials (APs) throughout the duration of the stimulus.