咳嗽是呼吸道自我保护的反射性防御行为,一个完整的咳嗽动作要经历如下几个环节,首先是吸气,肋间肌和膈肌放松,然后关闭声门,肋间肌和膈肌收缩,产生大约40Kpa的肺内压力,然后膈肌快速用力收缩同时声门猛然开放,肺内气体急速冲出呼吸道,将呼吸道黏膜上粘附的分泌物或异物喷出,最终形成一个咳嗽动作。
而这些复杂而协调的动作是由刺激神经末梢感受器产生冲动,经传入神经兴奋延髓的呼吸中枢,再由呼吸中枢发出冲动,经传出神经作用于肋间肌、膈和声门等而暴发咳嗽及咳痰,感受器冲动的传入咳嗽中枢和咳嗽中枢兴奋的传出主要通过迷走神经。
白天的时候,迷走神经的兴奋度相对来说不是很高,所以我们会感觉到白天的咳嗽往往不是很严重,而到了夜晚睡觉以后,由于迷走神经的兴奋度会增加,支气管平滑肌收缩,使支气管的管腔变形缩小,呼吸道的敏感性增加,再加上呼吸道分泌物的刺激,咳嗽就会变得更加剧烈和频繁,这就是晚上咳嗽厉害的关键原因。
Coughing is a reflex defensive behavior for airway self-protection. A complete coughing action goes through the following steps, first inhalation, relaxation of the intercostal muscles and diaphragm, then closing of the glottis, contraction of the intercostal muscles and diaphragm, resulting in about 40Kpa inner pressure. Then, the diaphragm muscle contracts rapidly and the glottis suddenly opens, and the air in the lungs quickly rushes out of the respiratory tract, ejecting the secretions or foreign bodies adhering to the respiratory mucosa, and finally forming a coughing action. These complex and coordinated actions are stimulated by nerve ending receptors to generate impulses, which excite the respiratory center of the medulla oblongata through afferent nerves, and then send out impulses from the respiratory center, which are triggered by efferent nerves acting on the intercostal muscles, diaphragm, and glottis. For coughing and expectoration, the afferent impulses of receptors to the cough center and the excitatory outflow of the cough center are mainly through the vagus nerve. During the day, the excitability of the vagus nerve is relatively low, so we will feel that the cough during the day is often not very serious, but after sleeping at night, due to the increase in the excitability of the vagus nerve, the bronchial smooth muscle contracts and makes the bronchial tubes. The cavity is deformed and reduced, the sensitivity of the respiratory tract increases, coupled with the stimulation of respiratory secretions, the cough will become more intense and frequent, which is the key reason for the severe cough at night.
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