2013C09 Describe the cough reflex.

 

List:

       Intro

       Afferent

       Controller

       Efferent

 

Intro:

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

 

Afferent limb:

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

 

Controller:

Afferents to

  Nucleus tractus solitarius

Integration

  Medullary respiratory centre

Efferents from

  Nucleus ambiguus (pharynx, larynx)

  Dorsal motor nucleus of vagus

 

Efferent limb:

 

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)

 

 

 

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