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Control of Breathing Shahd AlAlii
Breathing is controlled by centers in the brain stem:
Chemoreceptors
Mechanoreceptors
Control centers
Respiratory muscles
Medulla Respiratory Center:
Inspiratory center (DRG)
Controls the basic rhythm of respiration
Receive sensory input
Sends output
Inhibited by Pneumotaxic center
Expiratory center (VRG)
Responsible for expiration
Apneustic Center Abnormal breathing pattern “inspiratory gasps”
Prolonged inspiration
Stimulation in the lowers pons
Stimulation of these neurons excites the DRG
Pneumotaxic CenterTurns off inspiration
Limits the burst of AP
Lesion???
Hering-Breuer Reflex Initiated by the nerve receptors in the wall of
the bronchi and bronchioles .
When the lung is over stretched the receptors send signals through the vagi 2 the DRG
It decreases breathing rate by prolonging expiratory time
Seen in COPD & heavy exercise
Cerebral CortexCan override the automatic brain stem centers
temporarily.
Chemoreceptors Most important sensory information arriving to the brain stem concerning
PaO2 + Peripheral chemoreceptors
PaCO2 + Central chemoreceptors
Arterial pH
Central Chemoreceptors Located on the ventral surface of the medulla
near the point of exist of the (CN IX) & (CN X) nerves.
Communicate directly with the inspiratory center.
Sensitive to the changes
Indirectly to the PaCO2
Directly to the pH of CSF
CO2 Concentration Respiratory center excitation is the greatest
during the first few of increased CO2 con but gradually declines:
HCO3BBB
Blood
H+
Peripheral Chemoreceptors Carotid bodies: “glossopharyngeal nerve”
Aortic bodies “vagus nerve”
to the DRG
Increases the breathing rate:
1. Decrease in PaO2
2. Increase in PaCO2
3. Decrease in pH
Responds mostly to hypoxia <60mmHg
The frequency of discharge in the carotid bodies is very sensitive when in the PO2 ranges between 30 and 60 mmHg.
Stimulus Reflex Name
Receptor Effects
Lung inflation (prevents overinflation)
Hering-Breuer inflation reflex
Stretch receptors in smooth muscle of large & small airways (SARs)
Inhibit the DRG & apneustic center.
Mechanical or chemical irritation of airways
Cough Receptors in upper airways, tracheo-bronchial tree (RARs)
Cough & broncho-constriction
Joint & muscle receptors
Mechanoreceptors
Increase breathing rate (+DRG)