Poole Lecture 10 Control of Ventilation

Three basic elements of the respiratory control system:

Sensors that gather information

Central controller in the brain that receives and coordinates information

Effectors that drive ventilation

Forms a negative feedback loop

Neurons within the Pons and medulla of the brainstem

Control pattern of inspiration and expiration

Transection between the spinal cord and medulla arrests breathing, so…

breathing rhythmicity originates with the brainstem and not in the spinal cord or respiratory muscles

Cortex

Overrides the brainstem for voluntary control of breathing.

Voluntary hyperventilation

Doubling ventilation halves arterial PCO2 and elevates arterial pH

Voluntary hypoventilation

increases arterial PCO2 and decreases arterial pH

Muscles of inspiration

diaphragm, external intercostals, sternomastoids, and scalenes.

Muscles of expiration

abdominals and internal intercostals

Chemoreceptor

receptor which responds to an alteration in the chemical composition of the blood or fluid it is immersed in

Central Chemoreceptors

found close to the ventrolateral surface of the medulla in the brainstem.

What fluid do central chemoreceptors measure?

Brain extracellular fluid in which CO2 easily diffused from the blood vessel to the cerebralspinal fluid

Changes in arterial H+ do not effect

central chemoreceptors because they are situated behind the blood brain barrier that is impermeable to charged molecules

Peripheral chemoreceptors

located bilaterally at the bifurcation of the common carotid arteries and at the aortic arch

Peripheral chemoreceptors sensitivity

Alterations in arterial PO2, PCO2, and pH

sole direct sensor for reduced PO2 in the body that results in increased ventilation

How can chemoreceptor function be assessed?

Altering the chemical composition of the arterial blood by breathing from a bag containing low O2 or high CO2

Intrapulmonary chemoreceptors

Found in birds and reptiles, respond to low PCO2 in the lung and act to inhibit the depth of breathing (VT)

Midpontine sectioning

Causes prolonged inspiratory gasping. With vagi cut, inspiratory efforts are massively prolonged

Cutting the vagi

Induces slow, deep breathing

sectioning between the pons and medulla

little effect with intact vagi