Mechanism of Cough and SneezeApril 5, 2011 | 8:57 pm | Physiology | One Comment
Extrathoracic: nose, oropharynx, larynx, upper trachea
Intrathoracic: rapidly adapting irritant receptors in epithelium of lower trachea and large central bronchi
Other locations: tympanic membrane, diaphragm, stomach
Cough is an expulsive reflex that protects the lungs and respiratory passage from foreign bodies.
Causes of cough:
- Irritants-smokes, fumes, dusts, etc.
- Diseased conditions like COPD, tumors of thorax, etc.
- Pressure on respiratory tracts
Components of cough reflex:
- Cough receptors
- Afferent nerves
- Cough center
- Efferent nerves
- Effector muscles
Mechansim of cough reflex:
- Deep inspiration, closed glottis
- Increased intrapleural pressure then glottis opens suddenly with outflow of air at high velocity
- Leads to the expulsion of irritants from mouth only
Pathway for cough reflex:
- Receptors in nose, paranasal sinuses, pharynx, trachea, pleura, diaphragm, perichondrium, stomach, ex.auditory canal and tymphanic membrane
- Stimulus pass via V,IX,X cranial nerves and phrenic nerves. And reach to
- Cough centre in medulla
- Efferent nerves from medullary centre, X cranial nerve, phrenic nerve, spinal motor nerve
- Activation of primary and accessory respiratory muscles
Sneeze is defined as the involuntary expulsion of air containing irritants from nose.
Causes of sneeze:
- Irritation of nasal mucosa
- Excess fluid in airway
Components of sneeze reflex:
- Sneeze receptor
- Afferent nerve
- Sneeze center
- Efferent nerve
- Effector muscle
Mechanism for sneeze:
- Deep inspiration
- Opened glottis
- Expulsion of irritants from both nose and mouth
Pathway for sneeze reflex:
- Irritation of nasal mucosa
- Olfactory receptors or V cranial nerve endings
- Stimulus pass via I and V cranial nerve and reach to
- Sneeze centre in medulla – present in nucleus solitarious and reticular formation
- Efferent nerves from V, VII, IX, X cranial nerves and intercostal muscles
- Activation of pharyngeal, tracheal and respiratory muscles
Summary (Differences between coughing and sneezing):
Sneezing is stimulated by irritation of nasal mucosa. The impulses travel via the trigeminal nerve. Cough occurs due to the irritation of receptors in tracheobronchial tree. Impulses travel up via glossopharyngeal and vagus nerves.
In sneezing the air is trapped by shutting off its exit passages through the nasophaynx and the oral cavity. In coughing the air is trapped behind the closed glottis by contraction of the laryngeal adductor muscles.
In sneezing the air is released by opening the nasopharynx. In coughing, the air is released by opening the glottis.
Sneezing always occurs reflexly but coughing can be performed voluntarily also.
Prepared and presented by:
- Sulav Kumar Shrestha (80)
- Surakshya Rayamajhi (81)
- Surendra Pariyar (82)
Tags: cough, sneeze
Last updated: April 5, 2011