How Do We Cough? - The Mechanism of Coughing - Cough Reflex Animation - Learn Human Body

• published: 27 Dec 2014
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Coughing is a sudden expulsion of air from the lungs through the epiglottis at an amazingly fast speed (estimated at 100 miles per hour). With such a strong force of air, coughing is the body’s mechanism for clearing the breathing passageways of unwanted irritants. In order for a cough to occur, several events need to take place in sequence. First, the vocal cords open widely, allowing additional air to pass through into the lungs. Then the epiglottis closes off the windpipe (larynx), and simultaneously, the abdominal and rib muscles contract, increasing the pressure behind the epiglottis. With the increased pressure, the air is forcefully expelled, and creates a rushing sound as it moves very quickly past the vocal cords. The rushing air dislodges the irritant, making it possible to breathe comfortably again. ----- Cough A cough (About this sound pronunciation (help·info) Latin: tussis) is a sudden and often repetitively occurring reflex which helps to clear the large breathing passages from secretions, irritants, foreign particles and microbes. The cough reflex consists of three phases: an inhalation, a forced exhalation against a closed glottis, and a violent release of air from the lungs following opening of the glottis, usually accompanied by a distinctive sound.[1] Coughing is either voluntary or involuntary. Frequent coughing usually indicates the presence of a disease. Many viruses and bacteria benefit evolutionarily by causing the host to cough, which helps to spread the disease to new hosts. Most of the time, irregular coughing is caused by a respiratory tract infection but can also be triggered by choking, smoking, air pollution,[1] asthma, gastroesophageal reflux disease, post-nasal drip, chronic bronchitis, lung tumors, heart failure and medications such as ACE inhibitors. Treatment should target the cause; for example, smoking cessation or discontinuing ACE inhibitors. Cough suppressants such as codeine or dextromethorphan are frequently prescribed, but have been demonstrated to have little effect. Other treatment options may target airway inflammation or may promote mucus expectoration. As it is a natural protective reflex, suppressing the cough reflex might have damaging effects, especially if the cough is productive.[2] ------------------------------ The mechanism of cough How do we cough? What happens in you throat and lungs? This action reminds one of a pressure cooker blowing off steam. Sensing something is wrong… Both the upper and lower airways are lined by slow-reacting and fast reacting receptors which can respond to a number of different types of stimuli ranging from dust to irritant gases as well as excess mucus. Once the receptors are triggered, a signal is sent via the vagus nerve, setting up a reflex with the signal being transmitted to your brainstem and consciousness making you aware that you need to clear these noxious particles or gases. Preparing for the cough… The cough centre situated in the medulla in a matter of milliseconds, makes your consciousness aware of the fact that you need to cough as well as sending impulse back down to the diaphragm and intercostal rib muscles, preparing them for the cough action. The first action is that the diaphragm ‘drops’ to suck air into the chest filling the thoracic cavity. The second action following the diaphragm movement is the glottis or ‘voice box’ closes to prevent any air from leaving the chest. Finally the actual cough… Thereafter the cough centre triggers the diaphragm and intercostal muscles to contract, making the thoracic cavity smaller and building up pressure inside the chest… then the closed glottis opens allowing the high pressure air to suddenly escape from the chest through the airways hopefully taking with it any irritating particles, foreign bodies or phlegm which triggered the entire reflex to start with. Air leaving the chest can reach speeds of up to 200 km/h and even faster in the event of a sneeze! ----------------- Pathophysiology A cough is a protective reflex in healthy individuals which is influenced by psychological factors.[3] The cough reflex is initiated by stimulation of two different classes of afferent nerves, namely the myelinated rapidly adapting receptors, and nonmyelinated C-fibers with endings in the lungs. However it is not certain that the stimulation of nonmyelinated C-fibers leads to cough with a reflex as it's meant in physiology (with its own five components): this stimulation may cause mast cells degranulation (through an asso-assonic reflex) and edema which may work as a stimulus for rapidly adapting receptors.