The Japanese journal of physiology
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The upper airway is a vital part of the respiratory tract. Although the upper airway serves several functions, protection of the airway and preservation of airway patency are the most essential functions subserved by upper airway reflexes. Various types of nerve endings have been identified in and under the epithelium of the upper airway, and afferent nerve endings are the natural starting of all reflex activity. ⋯ Both depression and exaggeration of upper airway reflexes cause clinical problems. Depression of upper airway reflexes enhances the chance of pulmonary aspiration and compromises the maintenance of the airway, whereas exaggeration of airway reflexes such as laryngospasm and prolonged paroxysm of cough can be harmful and dangerous. In this review, various aspects of upper airway reflexes are discussed focusing on the functions of upper airway reflexes in humans and some pathophysiological problems related to clinical medicine.
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Review Comparative Study
Neuronal mechanisms of respiratory rhythm generation: an approach using in vitro preparation.
The respiratory network in the ventrolateral medulla of the brainstem-spinal cord preparation from newborn rat involves pre-inspiratory (Pre-I) neurons, three types of inspiratory (Insp I, II, III) neurons and two types of expiratory (Exp-i, Exp-p-i) neurons as major subtypes, which were classified according to patterns of postsynaptic potentials. The neuronal respiratory-related membrane potential fluctuations of these cells indicate at least four distinguishable phases of the in vitro respiratory cycle: pre-inspiratory, inspiratory, post-inspiratory (E1), and late-expiratory (E2). A current hypothesis for the central pattern generator of respiration proposed by our group is that Pre-I neurons in the rostral ventrolateral medulla, with intrinsic burster properties, produce the primary respiration rhythm. ⋯ Respiratory neuron networks in this preparation were compared with those of different in vitro preparations, like rhythmic slices or perfused brainstems and of adult mammals in vivo. Many types of synaptic connections among respiratory neurons in adult mammals were also found in the (rostral) ventrolateral medulla of a brainstem-spinal cord preparation from newborn rat. The characteristics of the inspiratory burst pattern and inspiratory off switch mechanisms in newborn rat preparations might be explained by insufficient inhibitory (or excitatory) synaptic inputs to the inspiratory pattern generator due to an immature neuron network and/or deafferentiation.
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Dehydration due to hyperthermia induces both hyperosmolality and hypovolemia. Hyperosmolality reduces evaporative cooling, and alters the thermal responsiveness of the hypothalamic center to changes in both the central and peripheral milieu. Hypovolemia also reduces the thermoregulatory response, but its effect is more variable. ⋯ Regulation of fluid replacement after thermal dehydration can be considered both from the point of view of osmoregulation and volume regulation. In the rehydration process, control of plasma osmolality precedes blood volume regulation, which also suggests that changes in blood volume sensed as changes in the CVP are regulated within a narrow range by various mechanisms. These findings suggest a hierarchic structure for the homeostatic mechanisms related to thermoregulation, with higher priority being given to the maintenance of cardiac output and the cellular volume of the brain at the expense of peripheral circulation and cell volume.