Normal Breathing

Normal Breathing

Normal breathing is controlled by two separate neural control systems; i.e. automatic and voluntary (the best analogy may be autopilot and human pilot control of an airplane).




Automatic System

Rhythmic discharge of brain stem respiratory neurons located in the medulla and pons (respiratory center) produces automatic respiration.

Corollary discharge reports to sensory cortex where respiratory effort is sensed.

Efferent output from respiratory motor neurons located in spinal cord reciprocally activates muscles of inspiration and of expiration.

Discharge is rhythmic and automatic (most efficient and with least effort).

The person is not usually not aware of breathing.

Voluntary System

Discharge from cerebral (motor) cortex activates respiratory motor neurons via corticospinal tract.

Corollary discharge goes to sensory cortex.

Afferent discharge is from the motor cortex (less efficient and more effort).

The person usually aware of breathing.

Afferent Inputs

Afferent inputs from chemoreceptors (blood and brain) as well as mechanoreceptors (airways, lungs and chest wall) integrate into the respiratory center for feedback and adjustment of respiratory patterns.

These afferent inputs may also project to higher brain centers to provide a direct appraisal of the chemical milieu of the body and of the mechanical status of the ventilatory apparatus.

Increased progesterone and salicylic poisoning change the rate of breathing, predominantly through chemo-receptors.

Obstructive and restrictive lung diseases mediate breathing, predominantly through mechano-receptors.

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