![]() Within the larynx there are several additional receptor types responsive to a range of modalities including pressure, respiratory drive, and cold. 24, 137, 141), but little is known about their reflex effects or central pathways, and they will not be considered further. Neuroepithelial bodies provide an additional airway receptor type (see reviews in Refs. The present minireview will focus on the central pathways mediating the reflexes evoked by these receptors. The major cardiorespiratory reflex effects of each of these are listed in Table 1. Within the airways below the larynx, three categories of receptor are typically identified: slowly (SAR) and rapidly (RAR) adapting stretch receptors and bronchopulmonary C fibers. The morphology and respiratory reflex effects of activating pulmonary and airway receptors have been the subjects of many excellent reviews ( 22– 24, 32, 83, 84, 87, 88, 95, 105, 125, 132, 137, 138, 141). Axon collaterals from both P-cells and RAR interneurons, and likely from NTS interneurons in the C-fiber pathway, project to the parabrachial pontine region where they may contribute to plasticity in respiratory control and integration of respiratory control with other systems, including those that provide for voluntary control of breathing, sleep-wake behavior, and emotions. P-cells and second order neurons in the RAR pathway also provide inputs to regions of the ventrolateral medulla involved in control of respiratory motor pattern, i.e., regions containing a predominance of bulbospinal premotor neurons, as well as regions containing respiratory rhythm-generating neurons. A subset of NTS neurons receiving afferent input from SARs (termed pump or P-cells) mediates the Breuer-Hering reflex and inhibits neurons receiving afferent input from RARs. The relative ease of selective activation of SARs, and to a lesser extent RARs, has allowed for more complete physiological and morphological characterization of the second and higher order neurons in these pathways than for C fibers. Second order neurons in the pathways from these receptors innervate neurons located in respiratory-related regions of the medulla, pons, and spinal cord. Central terminations of each group are found in largely nonoverlapping regions of the caudal half of the nucleus of the solitary tract (NTS). Lung sensory receptors with afferent fibers coursing in the vagus nerves are broadly divided into three groups: slowly (SAR) and rapidly (RAR) adapting stretch receptors and bronchopulmonary C fibers. ![]()
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