Cough, sneezing and swallowing reflexes

July 20, 2022

Introduction

These are collectively called respiratory protective reflexes.
Protects lungs and air passage from foreign particles.
These reflexes modify respiratory process so that elimination of foreign particles occurs.
Thus, foreign particles cannot enter into the respiratory tract.
Are involuntary in nature and occurs instantaneously in response to stimulus.

A) Cough reflex

One of the modified respiratory processes.
Expiration occurs forcely.
One of the protective reflexes.
Irritation caused in respiratory tract and external auditory canal results to cough reflex.

Image source: researchgate

Causes

Irritant agents are the main causes.
Several disorders produce it.
Cardiac disorders, pulmonary disorders and tumors in thorax are some reasons of it.
These disorders exert pressure in larynx, trachea, bronchi and lungs.

Mechanism

Reflex pathway

For coughing also, there are specific receptors.
These receptors are present in different locations.
Nose, para-nasal sinuses, larynx, pharynx, trachea, pleura, diaphragm, stomach, pericardium, etc. are some locations.
Afferent nerve fibers carry the impulse through vagus, trigeminal, glossopharyngeal and phrenic nerves.
Medulla oblongata is the centre for cough reflex.
Efferent nerves bring message from medullar centre.
Through vagus, phrenic and spinal motor nerves message are carried.
Primary and accessory respiratory muscles activates in response to this message.

B) Sneezing Reflex

Image source: toppr

Causes

Dust particles irritate the nasal mucus membrane.
Debris, mechanical obstruction of the airway and excess fluid accumulation in the nasal passage are also cause of it.

Mechanism

Deep inspiration initiates this reflex which is followed by forceful expiratory effort.
Glottis remains opened.
Irritant agents thus expulsed out of respiratory tract.

Reflex pathway

Irritation of nasal mucus membrane initiates this reflex.
Olfactory receptors and trigeminal nerves endings are located in this nasal mucosa.
Afferent nerve fibers pass through the trigeminal and olfactory nerves.
In medulla oblongata, sneezing center is present.
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.
Activation of the pharyngeal, tracheal, and respiratory muscles.

C) Swallowing (Deglutition) Reflex

Prevention of entrance of food particles into the air passage during swallowing.
A protective respiratory reflex.
While swallowing, respiration is halted or arrested for a while.
This is termed apnea i.e., temporary arrest of respiration.
Also called swallowing apnea or deglutition apnea if it occurs while swallowing food.
Occurs in pharyngeal stage, i.e., second stage of deglutition.
Thus, food particles entry to respiratory tract is prevented.
Receptors are present over tonsillar pillars in the pharynx region.