- 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
- 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.
- Deep inspiration initiates cough.
- This is followed by forced expiration with closed glottis.
- Intra-pleural pressure increases above 100 mm Hg.
- This opens the glottis suddenly.
- Explosive outflow of air occurs at high velocity.
- Velocity of air reaches up-to 960 km/hr.
- Thus, irritant substances are expulsed out of the respiratory tract.
- 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
- Similar to cough reflex, results in forced expiration.
- Irritation to nasal mucus membrane causes it.
Image source: toppr
- 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.
- Deep inspiration initiates this reflex which is followed by forceful expiratory effort.
- Glottis remains opened.
- Irritant agents thus expulsed out of respiratory tract.
- 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.
Image source: researchgate
Factors affecting swallowing reflex
- Weakness of muscle
- Position of body
- Swallow timing
- Changes in respiratory mechanics
- Changes in lung volume
Cough, sneezing and swallowing reflexes