2013C09 Describe the cough reflex.

· Intro

· Afferent

· Controller

· Efferent

Definition	· Forceful expiration to expel mucous or foreign material from airways. Keeps lower resp tract sterile. · Can be voluntary or involuntary
Sequence	· Fast inspiration · Close glottis · Contract chest and abdo wall · ↑Intrathoracic pressure (ITP) ~100mmHg · Release glottis · Expiration fast (80km/h) and turbulent (to expunge wall-adherent material)
Purpose	· Keep airways sterile
Significance to anaesthesia	· Suppressed under GA – hypnotics, opioids · Risk of aspiration

Sensors

· Mucosal irritant receptors on C fibres

· Mechanical or chemical stimuli. E.g. water, food, dust

· From pharynx to resp bronchioles, esp carina

Pathway

· General visceral afferents: via dorsal horn and spinomedullary tract

· CNIX: pharynx -> nucleus tractus solitarius (NTS)

· CNX: -> the NTS

o Pharynx: own branch x 2

o Larynx above vocal cords: internal branch of superior laryngeal nerve x 2

o Larynx below vocal cords, trachea, bronchi: recurrent laryngeal nerve x 2

Afferents to

· Nucleus tractus solitarius

Integration

· Medullary respiratory centre

Efferents from

· Nucleus ambiguus (pharynx, larynx)

· Dorsal motor nucleus of vagus

	Muscle	Innervation
Inspiration	Diaphragm	C3-5
	External intercostals	Intercostal nerves
	Pharyngeal dilators	CNIX CNX pharyngeal branches
Glottic closure	Lateral cricoarytenoid Interarytenoid	CNX recurrent laryngeal
Increased intrathoracic pressure	Internal intercostals	Intercostal nerves
	Abdominals (rectus, transversus, internal and external obliques)	Lower intercostal nerves Subcostal nerves Iliohypogastric Ilioinguinal
	Latissimus dorsi	Thoracodorsal nerve
	Serratus posterior inferior	Intercostal nerves
	Quadratus lumborum	Subcostal nerve
Glottic release	Posterior cricoarytenoid (and relax glottic closure muscles)	CNX recurrent laryngeal
Forceful expiration	(as for increased intrathoracic pressure)