COUGH REFLEX
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"Cough"[MeSH Terms] AND reflex
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cough reflex physiology vagal afferents medulla authoritative
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3415124
Cough reflex
The cough reflex is a protective airway-defense mechanism that removes mucus, inhaled particles, and irritants from the larynx and tracheobronchial tree.
Reflex arc
| Component | Pathway |
|---|---|
| Stimulus | Mechanical irritation, mucus, smoke, dust, cold air, aspirated material, or chemical irritants |
| Receptors | Mainly in the larynx, trachea, carina, and large bronchi. They include mechanoreceptors and chemosensitive vagal nerve endings. |
| Afferent limb | Primarily the vagus nerve, especially the superior laryngeal and recurrent laryngeal branches |
| Central integration | Medullary and pontine brainstem networks, often termed the “cough center”; cortical centers can voluntarily initiate or suppress cough |
| Efferent limb | Vagus to laryngeal muscles, phrenic nerve to diaphragm, and spinal motor nerves to intercostal and abdominal muscles |
| Response | Coordinated cough maneuver |
Three mechanical phases
-
Inspiratory phase
A deep inspiration provides sufficient lung volume. -
Compression phase
The glottis closes while expiratory muscles, diaphragm, intercostals, and abdominal muscles contract. This sharply raises intrathoracic pressure. -
Expiratory phase
The glottis opens suddenly, producing high-velocity airflow that dislodges and expels secretions or foreign material.
Clinical relevance
- A reduced cough reflex increases aspiration and pneumonia risk, particularly in older adults and people with impaired consciousness, neuromuscular disease, stroke, or sedative/opioid exposure.
- A hypersensitive cough reflex contributes to chronic refractory cough. Acid, capsaicin, airway inflammation, viral infection, reflux, and upper-airway irritation can lower the cough threshold.
- Mechanical stimulation of the external ear canal may rarely trigger cough through the auricular branch of the vagus nerve, called the Arnold nerve cough reflex.
A detailed neurophysiology review describes vagal afferent input to the medulla and motor output through vagal, phrenic, and spinal nerves, as well as the three cough phases in this NCBI review. The textbook library also notes that cough reflex impairment is an important risk factor in aspiration pneumonia, especially in older patients.
Recent systematic reviews retrieved were about cough monitoring, dysphagia-related upper-airway sensory testing, and cough-sound classification, rather than evidence that materially changes this basic physiology.
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