20B08: Exam Report

Describe the cough reflex.

62% of candidates passed this question.

Overall, this question was reasonably well answered. Those that performed well had suitably detailed knowledge and structured their responses which generally included a definition and purpose of the reflex as well as the identification and a description of the afferent, integrator/controller, and efferent limbs of the reflex. This structure allowed a logical platform for the elucidation of the detail required in the answer, including types of stimulus, receptors, nerves (for both limbs of the reflex) and the muscles used in the phasic response to be clearly articulated.

14A13: Exam Report

Describe the cough reflex.

26% of candidates passed this question.

Many candidates struggled with this question.  A good answer included a brief description of the role of the cough reflex, an outline of the sensory pathways, central integration and motor pathways  of  the  reflex,  and  a  description  of  the  components  of  the  cough  reflex.    Most candidates failed to accurately describe the sequence of events involved in the cough reflex. Very few gave sufficient detail on the nerve supply of the larynx

F10v / 20B08 / 14A13: Describe the Cough Reflex


  • Protects airways from noxious substances
  • Helps clear excess bronchial secretions
  • Also one of the tests to establish brain death → can be involuntary/voluntary
  • Inhalation of gas above FRC → closure of glottis → ↑intrapleural P 100cm H2O → reflex opening of glottis with turbulent expiratory flow

Afferent Limb – Vagus (X)

  • Cough receptors stimulated by irritant
    • Extrathoracic: nose, oropharynx, larynx, upper trachea
    • Intrathoracic: Rapidly acting irritant receptors on lower trachea & central bronchi
  • Signal transmitted by Vagus (X) nerve

Central Processing

  • Central integration of airway afferents is poorly understood
  • Occurs at level of Brainstem (Medulla)

Efferent Limb

  • Signal transmitted back via Vagus (X) n.
  • Allows coordinated action of inspiratory m., pharyngeal m. & expiratory m.

Cough Mechanism

  • Diaphragm (Phrenic) & External IC (IC n’s) contract, creating a negative pressure around lung
  • Air rushes into lungs in order to equalise P
  • Glottis closes (Recurrent Laryngeal n.)
  • Expiratory muscles activate against closed glottis
  • ↑intrathoracic P up to 300mmHg which is transmitted to arterial blood & CSF
  • Vocal cords relax → glottis opens
  • Air released at 100mph
  • Drags & expels irritant