CorpusHuman Anatomy
RespiratoryPhysiological process

Cough and sneeze reflexes

Also known as: cough, sneeze, tussive reflex

Protective reflexes that expel irritants: the cough clears the larynx, trachea and bronchi (vagal afferents); the sneeze clears the nasal cavity (trigeminal afferents).

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Overview

Cough. Irritant (rapidly adapting) receptors and C-fibre endings in the larynx, trachea (especially the carina) and large bronchi are stimulated by mechanical or chemical irritants. Afferents travel in the vagus (internal laryngeal nerve from the larynx) to the medulla, which coordinates three phases: (1) inspiratory — rapid intake of up to ≈2.5 L of air; (2) compressive — the glottis and epiglottis close and the abdominal and internal intercostal muscles contract forcefully, raising intrathoracic pressure to ≈100 mmHg or more; (3) expulsive — the glottis suddenly opens and air explodes outward at velocities reported up to ≈75–100 miles per hour (≈120–160 km/h), while dynamic compression narrows the airways and further accelerates airflow, shearing mucus and particles from the walls.

Sneeze. Irritation of the nasal mucosa activates trigeminal (CN V) afferents; the sequence resembles a cough, but the uvula and soft palate are depressed so a large volume of air is forced through the nose as well as the mouth.

Location

Receptors in the larynx, trachea, carina and bronchi (cough) and nasal mucosa (sneeze); integration in the medulla.

Anatomy

Innervation

Afferent: vagus (CN X; internal laryngeal and pulmonary branches) for cough — also the auricular branch of the vagus (ear-canal cough); trigeminal (CN V) for sneeze. Efferent: phrenic, intercostal and abdominal nerves; recurrent laryngeal nerve (glottic closure).

Function

  • Expel foreign material, mucus and irritants from the airways.
  • Protect the lower airway from aspiration.

Clinical significance

Chronic cough

Persistent cough (> 8 weeks) in a non-smoker with a normal chest radiograph is most often due to upper-airway cough syndrome (post-nasal drip), asthma or gastro-oesophageal reflux; ACE inhibitors cause a dry cough in ≈10% of users via bradykinin and substance P accumulation.

Impaired cough and aspiration

Stroke, anaesthesia, sedation, neuromuscular disease and internal laryngeal nerve injury blunt the cough reflex, causing silent aspiration and pneumonia.

Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.