Applied Resp – Cough reflex

Master answer

Afferent

• In response to chemical, mechanical or noxious stimuli in larynx, trachea, carina or bronchi
• Signal transduced via internal laryngeal nerve (vagus nerve)

Central processor

• Medullary respiratory centre
  • No single “cough centre” isolated

Efferent

Co-ordinated action of inspiratory muscles, pharyngeal muscles, and expiratory muscles

1. Inspiratory phase
   • Inhalation of a volume of air sufficient for cough generation (phrenic nerve and intercostal nerves)
2. Compressive phase
   • Closure of the glottis (recurrent laryngeal nerve)
   • Activation of expiratory muscle against closed glottis
   • Generation of transient increase in pressure of 300mmHg in thorax arterial blood and CSF
3. Expulsive phase
   • Opening of glottis due to posterio-cricoarytenoid muscle activation
   • High velocity flow generated in bronchi, trachea and larynx
     • “Choke point” – high velocity flow causes turbulant flow → increased shear stress between gas and airway lining → drag and expulsion of irritant

Intrinsic muscles of the larynx

• Cricothyroid
  • Upper lip of cricoid cartilage → Inferior aspect of thyroid cartilage
  • Innervated by superior laryngeal nerve
  • Tenses vocal cords – elevates vocal tone
• Thyroarytenoid
  • Anterior inner surface of thyroid à arytenoid cartilage
  • Innervated by inferior laryngeal nerve
  • Relaxes vocal cords – depresses vocal tone
• Posterior cricoarytenoid
  • Posterior aspect of cricoid cartilage → arytenoid cartilage
  • Innervated by inferior laryngeal nerve
  • Abducts vocal cords
• Lateral cricoarytenoid
  • Lateral aspect of cricoid cartilage → arytenoid cartilage
  • Innervated by inferior laryngeal nerve
  • Adducts vocal cords
• Transverse and Oblique arytenoids
  • Spans the arytenoid cartilages
  • Innervated by the inferior laryngeal nerve
  • Adducts vocal cords

Sakurai 2016

Answer by Sakurai