1. Normal Physiology:

Respiratory control is not an entirely "autopilot" process, but a result of complex interactions between neurons in the brainstem. 3 basic processes occurring simultaneously:

• Central generation (and maintenance) of a "baseline" respiratory rhythm.
• Modulation of the "baseline" rhythm by central and peripheral feedback loops.
• Recruitment of respiratory muscles appropriate for the task.

As a result, respiratory centers in the brainstem are continuously introducing changes "on line" so as to adjust pattern and strategy of breathing to one that results in minimal energy expenditure.

A. Central Pattern Generation: 3 groups of Neurons in brainstem

1. Dorsal respiratory group (tractus solitarious)
2. Ventral respiratory group (Btzinger complex, nucleus retroambigualis and nucleus ambiguus)
3. Pontine respiratory group (Klliker-Fuse complex and nucleus parabrachialis medialis)

Neurons in the different groups have different patterns of activation, then their activity is not uniform throughout the respiratory cycle. Altogether, coordinated activity of neurons in respiratory groups generates respiratory pattern.

B. Sensory Feedback System: Multiple afferent pathways surveying for changes in thoracic cavity, lung tissue, airways, blood and respiratory muscles.

Receptor	Response	Importance
Facial cutaneous receptors	inhibitory	newborn
nasal mucosal receptors	inhibitory	infants
laryngeal receptors	inhibitory	most potent
Airway smooth muscle receptors	inhibitory	Hering-Breuer reflex
Lung parenchyma stretch receptor	inhibitory	delay inspiration
Lung J receptors	excitatory	pulmonary edema
Bronchial irritant receptors	inhibitory	shorten inspiration
Central chemoreceptors (?medulla)	excitatory	H Pco2, L pH (H high, L low)
	inhibitory	L Pco2, H pH
Carotid body (peripheral chemoreceptor)	excitatory	L Po2, H Pco2, L pH
	inhibitory	H Po2, L Pco2, H pH
Aortic body (peripheral chemoreceptor)	excitatory	L Po2, H Pco2, L pH
	inhibitory	H Po2, L Pco2, H pH

C. Muscular activity:

A simplified representation of the integrated system will look like this:

Click here to go to Part 2: Development of Respiratory Control.

Index Normal Physiology Development of Respiratory Control Definitions Specific Disorders Readings

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