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)