RESPIRATORY REFLEXES

 

  

RESPIRATORY REFLEXES

Respiratory reflexes are the reflexes that protect lungs and air passage from foreign particles. Respiratory process is modified by these reflexes in order to eliminate the foreign particles or to prevent the entry of these particles into the respiratory tract.

Following are the respiratory protective reflexes:

COUGH REFLEX

Cough is a modified respiratory process characterized by forced expiration. It is a protective reflex and it is caused by irritation of respiratory tract and some other

areas such as external auditory canal.

Causes

Cough is produced mainly by irritant agents. It is also produced by several disorders such as cardiac disorders (congestive heart failure), pulmonary disorders (chronic obstructive pulmonary disease – COPD) and tumor in thorax, which may exert pressure on larynx, trachea, bronchi or lungs.

Mechanism

Cough begins with deep inspiration followed by forced expiration with closed glottis. This increases the intrapleural pressure above 100 mm Hg. Then, glottis opens suddenly with explosive outflow of air at a high velocity. Velocity of the airflow may reach 960 km/hour. It causes expulsion of irritant substances out of the

respiratory tract.

Reflex Pathway

Receptors that initiate the cough are situated in several locations such as nose, paranasal sinuses, larynx, pharynx, trachea, bronchi, pleura, diaphragm, pericardium, stomach, external auditory canal and tympanic membrane. Afferent nerve fibers pass via vagus, trigeminal, glossopharyngeal and phrenic nerves. The center for cough reflex is in the medulla oblongata. Efferent nerve fibers arising from the medullary center pass through the vagus, phrenic and spinal motor nerves. These nerve fibers activate the primary and accessory respiratory muscles.

SNEEZING REFLEX

Sneezing is also a modified respiratory process characterized by forced expiration. It is a protective reflex caused by irritation of nasal mucous membrane.

Causes

Irritation of the nasal mucous membrane occurs because of dust particles, debris, mechanical obstruction of the airway and excess fluid accumulation in the nasal passages.

Mechanism

Sneezing starts with deep inspiration, followed by forceful expiratory effort with opened glottis resulting in expulsion of irritant agents out of respiratory tract.

Reflex Pathway

Sneezing is initiated by the irritation of nasal mucous membrane; the olfactory receptors and trigeminal nerve endings present in the nasal mucosa. Afferent nerve fibers pass through the trigeminal and olfactory nerves. Sneezing center is in medulla

oblongata. It is located diffusely in spinal nucleus of trigeminal nerve, nucleus solitarius and the reticular formation of medulla. Efferent nerve fibers from the medullary center pass via trigeminal, facial, glossopharyngeal, vagus and intercostal nerves. These nerve fibers activate the pharyngeal, tracheal and respiratory muscles.

SWALLOWING (DEGLUTITION) REFLEX

Swallowing reflex is a respiratory protective reflex that prevents entrance of food particles into the air passage during swallowing. While swallowing of the food, the respiration is arrested for a while. Temporary arrest of respiration is called apnea. Arrest of breathing during swallowing is called swallowing apnea or deglutition apnea. It takes place during pharyngeal stage, i.e. second stage of deglutition and prevents entry of food particles into the respiratory tract.