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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
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
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
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
Who is responsible for expiration?
Ventral Respiratory Group
Who is responsible for inspiration?
Dorsal Respiratory Group
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
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
Where is the central chemoreceptors located?
Bilaterally in the ventrolateral medulla
What are central chemoreceptors sensitive to?
Which chemoreceptor is most sensitive to PCO2?
Where is the peripheral chemoreceptors located?
Aortic arch (aortic bodies) and carotid arteries (carotid bodies)
What are peripheral chemoreceptors sensitive to?
How does the chemoreceptors respond to hypercapnia?
Hyperventilation - Stimulates breathing
How does the chemoreceptors respond to hypoxia?
Hyperventilation - Increases breathing rate
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
What is the hypercapnic drive?
- When arterial PCO2 is above normal
- Stronger than hypoxic drive
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
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
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