Cough, sneezing and swallowing reflexes

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.

Types of Cough Reflex. The pattern of the cough reflex depends on the... |  Download Scientific Diagram

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

  • 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.

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

  • Similar to cough reflex, results in forced expiration.
  • Irritation to nasal mucus membrane causes it.

What is a Reflex Arc? Draw a flowchart showing of events which occur during  sneezing.

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.

Framework of the control of reflex swallowing. Solid line and broken... |  Download Scientific Diagram

Image source: researchgate

Factors affecting swallowing reflex

  1. Weakness of muscle
  2. Position of body
  3. Swallow timing
  4. Changes in respiratory mechanics
  5. Changes in lung volume

References: 

i) https://en.wikipedia.org/wiki/Cough_reflex

ii) https://www.britannica.com/science/sneeze-reflex

Cough, sneezing and swallowing reflexes

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