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What are the roles of the brainstem in terms of how it regulates breathing?
- PreBotzinger Complex
- Dorsal Respiratory Group
- Ventral Respiratory Group
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What is the role of the PreBotzinger Complex and where is it located?
- Medulla Oblongata
- Sets the basic rhythm for normal breathing
- Contains pacemaker cells that create pacemaker potentials
- Coordinates the activities of the DRG and VRG
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What is the role of the Dorsal Respiratory Group and where is it located?
- Medulla Oblongata
- Primarily responsible for inspiration
- CNX - inputs info from peripheral chemoreceptors and mechanoreceptors (e.g. lung stretch receptors, irritant receptors and joint and muscle receptors)
- CNIX - inputs info from peripheral chemoreceptors
- Output from DRG travels via the phrenic nerve to the diaphragm and external intercostals
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What is the role of the Ventral Respiratory Group and where is it located?
- Medulla Oblongata
- Primarily responsible for expiration
- Not active during normal, quiet breathing, when expiration is passive
- Activated (e.g during exercise) when expiration becomes an active process
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Who is responsible for expiration?
Ventral Respiratory Group
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Who is responsible for inspiration?
Dorsal Respiratory Group
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What is the role of the Apneustic Center and where is it located?
- Lower Pons
- Stimulates inspiration, producing deep and prolonged inspiratory gasps (apneusis), followed by occasional brief exhalations
- Stimulation of these neurons apparently excites the inspiratory center in the medulla, prolonging the period of action potentials in the phrenic nerve, and thereby prolonging the contraction of the diaphragm
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What is the role of the Pneumotaxic Center and where is it located?
- Upper Pons
- Inhibits inspiration and limits the burst of action potentials in the phrenic nerve
- Limits the size of the TV
- Damage to the pneumotaxic center causes long, deep breathing
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Where is the central chemoreceptors located?
Bilaterally in the ventrolateral medulla
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What are central chemoreceptors sensitive to?
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Which chemoreceptor is most sensitive to PCO2?
Central chemoreceptor
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Where is the peripheral chemoreceptors located?
Aortic arch (aortic bodies) and carotid arteries (carotid bodies)
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What are peripheral chemoreceptors sensitive to?
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How does the chemoreceptors respond to hypercapnia?
Hyperventilation - Stimulates breathing
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How does the chemoreceptors respond to hypoxia?
Hyperventilation - Increases breathing rate
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What is the hypoxic drive?
- When pts w/ pulmonary disease retain their CO2, elevating their PCO2 and chemoreceptors will adapt to this.
- A declining PO2 acting on the O2-sensitive peripheral chemoreceptors provides the principal respiratory stimulus
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What is the hypercapnic drive?
- When arterial PCO2 is above normal
- Stronger than hypoxic drive
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What/ Where is the Herring-Breur reflex and how does it effect breathing?
- Found in smooth muscle airways
- When excessively stretched, the lung stretch receptors send impulses via the vagus nerves to the brainstem, which then produces a decrease in breathing frequency
- A protective reflex to prevent over-expansion of the lung
- Not used during normal respiration but become increasingly active w/ labored breathing associated w/ vigorous exercise or climbing
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What is the irritant receptors (irritant reflexes) and how does it effect breathing?
- Between epithelial cells lining the airways
- Info from these receptors travels to the brainstem via the vagus nerves and causes a reflex constriction of bronchial smooth muscle and an increase in breathing rate
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What is the joint/ muscle receptors (proprioceptor reflexes) and how does it effect breathing?
- Increased activity of stretch receptors is sent to the brainstem (via the vagus nerves), and results in increased rate and depth of respiration ("proprioceptor reflex")
- Effect is very rapid, and shows an "added value" to stretching before exercise
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