Unlike the cutaneous afferent innervation, where A fibers innervate specific anatomical structures like Merkel cells, Ruffini endings, Hair Lanceolates, and Pacinian or Meissner corpuscles, the dogma associated with the vast majority of visceral sensory endings has been for many years that the peripheral arborizations of small myelinated and unmyelinated afferent fibers terminate as free nerve endings without any clear anatomic specialization. Despite this, it is clear from numerous studies utilizing neuronal tracing techniques that these peripheral terminals of vagal and spinal afferents can be localized within the different layers gastrointestinal tract, giving an indication to their physiological characteristics and functional roles. Three types of specialized endings have been identified in the gut wall, intraganglionic laminar endings (IGLEs), intramuscular arrays (IMAs), and mucosal endings (Fig. 2).
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