PRIMARY FUNCTION OF RESPIRATION: SUPPLY SUFFICIENT OXYGEN & REMOVE CARBON DIOXIDE
To sustain life, breathing must be cyclic, continuous and achieved by rhythmic contraction and relaxation of respiratory muscles by SOMATIC NERVOUS SYSTEM controlled by NEURAL & CHEMICAL factors.
Some systems like HEART can function without NERVOUS SYSTEM , RESPIRATORY SYSTEM can not function without it.
ROLE OF VAGUS –> The “Hering -Breuer Inflation reflex“. Large Tidal volume -> Stimulates pulmonary stretch receptors( located within smooth muscles of airway) -> afferents via Vagus to Medullary centres (DRG) -> INHIBIT Inspiratory neurons (SWITCH OFF INSPIRATORY RAMP).
DORSAL RESPIRATORY GROUP
INSPIRATORY NEURONS. It has interconnections with other centres.
VENTRAL RESPIRATORY GROUP
It is INACTIVE during quiet breathing (NO DISCHARGE). Active only when demand for ventilation increases. For example – exercise.
Damage to both DRG & VRG doesn’t stop respiration but decreases the amplitude of Phrenic Nerve activity. So, these sites are NOT obligatory for respiration.
INSPIRATORY RAMP SIGNAL
Ramp – like discharge in Inspiratory neurons.
Rate of rise of ramp –> related to lung volume.
Begins weakly, increases steadily for 2 seconds then ‘switches off’ –> latent period (passive expiration) –> again ramp signal.
these ramp signals result in steady increase in lung volume and not resulting in gasps due to sudden increase in gas and lung volume.
INTEGRATION & OPERATION
Juxta pulmonary capillary Receptor
Located in alveolar wall
Sensitive to the content of interstitial Fluid between the capillary endothelium & alveolar epithelium, so they respond to –> Pulmonary congestion, embolism, oedema, inhalation of strong irritants/chemicals.
J receptors role in exercise –> due to increase in interstitial fluid –> J receptors are stimulated –> inhibit stretch reflex –> limit the power of contraction of skeletal Muscle –> J-REFLEX
HERING-BREUER DEFLATION REFLEX à decrease in duration of expiration produced by marked deflation of lung.
TRANSECTION AT DIFFERENT LEVELS
‘ LIVE EVERY MOMENT, LIVE EVERY DAY – BUT AT THE END OF THE DAY – JUST BE THANKFUL THAT YOU ARE ALIVE & BREATHING’