And chemosensors are readily identified (described below). Regardless of the afferentAnd chemosensors are readily identified

And chemosensors are readily identified (described below). Regardless of the afferent
And chemosensors are readily identified (described below). Regardless of the AMN107 web afferent fiber, the majority of airway afferent nerves originate in the vagal sensory ganglia (nodose or jugular) [13,14]. A small population of fibers (believed to be a subpopulation of chemosensitive nerves) may have their origin in dorsal root ganglia adjacent to the upper thoracic spinal cord [15]. Little is known about the role of spinal afferents in airway defense.Low threshold mechanosensors Two classic types of low threshold mechanosensors have been described in the intrapulmonary airways of a number of mammalian species, namely the rapidly adapting receptors (RARs) and slowly adapting receptors (SARs) [8,9,16-20]. However, when comparing only a limited number of phenotypic traits RARs and SARs may appear indistinguishable (Table 1). Thus, RARs and SARs both originate in the nodose ganglia, terminate in the intrapulmonary airways and lung parenchyma, conduct action potentials in the A-range (10?0 m/s) and are sensitive to many mechanical stimuli, including changes in lung volume, airway smooth muscle constriction and airway wall oedema [9,12,17-21]. Accordingly, RARs and SARs may both display activity when the lungs are inflated [9,16-19]. RARs and SARs are also both generally insensitive to a wide range of chemical stimuli, unless the stimulus evokes coincidental changes in airway smooth muscle tone, mucus secretion or airway wall volume [8,17,19].Airway sensory nerves do not form a homogeneous population. However, to date, there is no single classification scheme that adequately and unambiguously subcategorizes the various afferent nerve subtypes that have been described in the airways. Although a functional classification is commonly employed (describing the PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/27766426 physiological responsiveness of airway afferents), subtypes can be alternatively delineated based on their origin, location in the airways, neurochemistry, electrophysiological properties or by the reflexes that are evoked secondary to afferent activation [4]. This lack of a universal classification scheme, coupled with attempts to classify an afferent subtype using only one phenotypic trait, often leads to some confusion as to the identity of a given afferent nerve type. It is therefore desirable to consider multiple characteristics when defining an airway afferent fiber. In guinea pigs (and likely true for all mammals) airway sensory nerves can be broadly functionally classified as either primarily mechanically sensitive (low threshold mechanosensors) or primarily chemically sensitive (chemosensors or alternatively, nociceptors) (Fig 1). Low threshold mechanoreceptors are readily activated by one PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/27693494 or more mechanical stimuli, including lung inflation, bronchospasm or light touch, but generally do not respond directly to chemical stimuli unless the stimulus acts upon airway structural cells to result in mechanical distortion of the nerve terminal [5-8]. Conversely, chemosensors are typically activated directly or sensitized by a wide range of chemicals, including capsaicin, bradykinin, adenosine, PGE2, but are relatively insensitive to mechan-Nevertheless, RARs and SARs can be differentiated by comparing their individual mechanical activation profiles, mechanical adaptation properties, central termination patterns and the reflexes that each precipitate (Table 1). Thus, RARs may be activated during both inflation and deflation of the lungs (including lung collapse) [9,17]. SARs, on the other hand,.