Cough reflex

Cough reflex

The cough reflex has both sensory (afferent) and motor (efferent) components. Pulmonary irritant receptors (cough receptors) in the epithelium of the respiratory tract are sensitive to both mechanical and chemical stimuli. Stimulation of the cough receptors by dust or other foreign particles produces a cough, which is necessary to remove the foreign material from the respiratory tract before it reaches the lungs.

The cough receptors, or rapidly adapting irritant receptors are located mainly on the posterior wall of the trachea, pharynx, and at the main carina, the point where the trachea branches into the main bronchi. The receptors are less abundant in the distal airways, and absent beyond the respiratory bronchioles. When triggered, impulses travel via the internal laryngeal nerve, a branch of the superior laryngeal nerve which stems from the (vagus nerve) (CN X), to the medulla of the brain. This is the afferent neural pathway. Unlike other areas responsible for involuntary actions like swallowing, there is no clearly identifiable area that can be labeled as the cough center in the brain.

The efferent neural pathway then follows, with relevant signals transmitted back from the cerebral cortex and medulla via the vagus and superior laryngeal nerves to the glottis, external intercostals, diaphragm, and other major inspiratory and expiratory muscles. The mechanism of a cough is as follows:

  • Diaphragm (innervated by phrenic nerve) and external intercostal muscles (innervated by segmental intercostal nerves) contract, creating a negative pressure around the lung.
  • Air rushes into the lungs in order to equalise the pressure.
  • The glottis closes (muscles innervated by recurrent laryngeal nerve) and the vocal cords contract to shut the larynx.
  • The abdominal muscles contract to accentuate the action of the relaxing diaphragm; simultaneously, the other expiratory muscles contract. These actions increase the pressure of air within the lungs.
  • The vocal cords relax and the glottis opens, releasing air at over 100 mph.
  • The bronchi and non-cartilaginous portions of the trachea collapse to form slits through which the air is forced, which clears out any irritants attached to the respitory lining.

Stimulation of the auricular branch of the vagus nerve supplying the ear may also elicit a cough. This is known as Arnold's reflex. Respiratory muscle weakness, tracheostomy, or vocal cord pathology (including paralysis or anesthesia) may prevent effective clearing of the airways.

The reflex is impaired in the person whose abdominals and respiratory muscles are weak. This problem can be caused by disease condition that lead to muscle weakness or paralysis, by prolonged inactivity, or as outcome of surgery involving these muscles. Bed rest interferes with the expansion of the chest and limits the amount of air that can be taken into the lungs in preparation for coughing, making the cough weak and ineffective. This reflex may also be impaired by damage to the internal branch of the superior laryngeal nerve which relays the afferent branch of the reflex arc. This nerve is most commonly damaged by swallowing a foreign object, such as a chicken bone, resulting in it being lodged in the piriform recess (in the laryngopharynx) or by surgical removal of said object.

References



Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • cough, reflex —    A cough induced by intestinal, gastric or uterine irritation, and not from respiratory causes …   Herbal-medical glossary

  • cough reflex — the sequence of events initiated by the sensitivity of the lining of the airways and mediated by the medulla as a consequence of impulses transmitted by the vagus nerve, resulting in coughing, i.e., the clearing of the passageways of foreign… …   Medical dictionary

  • Cough — A young boy coughing due to pertussis (Whooping Cough). ICD 10 R05 ICD …   Wikipedia

  • cough — cougher, n. /kawf, kof/, v.i. 1. to expel air from the lungs suddenly with a harsh noise, often involuntarily. 2. (of an internal combustion engine) to make a similar noise as a result of the failure of one or more cylinders to fire in sequence.… …   Universalium

  • Cough center — The cough center of the brain is a region of the brain which controls coughing, located in the medulla oblongata area of the brain. Antitussives and other cough medicines focus their action on the cough center. See also Cough reflex Respiratory… …   Wikipedia

  • Cough — Cough, n. [Cg. D. kuch. See {Cough}, v. i. ] 1. A sudden, noisy, and violent expulsion of air from the chest, caused by irritation in the air passages, or by the reflex action of nervous or gastric disorder, etc. [1913 Webster] 2. The more or… …   The Collaborative International Dictionary of English

  • Reflex — A reaction that is involuntary. The corneal reflex is the blink that occurs with irritation of the eye. The nasal reflex is a sneeze. * * * 1. An involuntary reaction in response to a stimulus applied to the periphery and transmitted to the… …   Medical dictionary

  • Cough — A rapid expulsion of air from the lungs typically in order to clear the lung airways of fluids, mucus, or material. Also called tussis. * * * 1. A sudden explosive forcing of air through the glottis, occurring immediately on opening the… …   Medical dictionary

  • reflex cough — a cough due to the irritation of some remote organ …   Medical dictionary

  • laryngeal reflex — a cough produced by irritating the larynx. * * * a type of cough reflex in which irritation of the fauces and larynx causes cough …   Medical dictionary

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”