Week 10 Flashcards
Respiratory control center
Breathing originates from a central pattern generator in the brainstem (medulla and pons)
How can CPG be divided?
- Sites that generate breathing rhythm
- Downstream sites that form the motor pattern and synapse with efferent motor neurons
Central Rhythm generator
Rhythmic groups of neurons that area active during inspiration (prebotC), post-inspiration (PiCo), and expiration (pF)
Ventral Respiratory Group
Includes the central rhythm generator and the motor pattern generators neurons
- Controls the activity of respiratory muscles
Pontine respiratory group
Modulates output from the ventral respiratory group
What nerves innervate the respiratory muscles?
- Diaphragm: phrenic nerve
- External intercostals: External intercostal nerves
- Internal Intercostals: Internal intercostal nerves
- Airway muscles are also controlled by the CPG via cranial nerves
Sensory input to central pattern generators
- Peripheral sensory receptors send afferent information to the NTS in the dorsal medulla
- Interneurons connect sensory afferents in the NTS to the ventral respiratory group and thus modulate its output
- Also have central chemoreceptors in the medulla that modulate VRG output
Hypoxic Ventilatory Response
- Reductions in arterial PO2 lead to an increase in ventilation
- Small declines in PO2 below normal arterial values can be fully corrected by increasing ventilation
- Larger declines in arterial PO2 cannot be fully compensated, but the increase in ventilation reduces the magnitude of PO2 decline
Peripheral O2 Chemoreceptors
- Primary O2 chemoreceptors are located in the carotid bodies, but the aortic bodies also play a role in the HVR
- Afferent neurons form synapse with interneurons in the NTS, which transmit the sensory information to the central pattern generator
How do the carotid bodies become activated and send AP
- Not well understood sensor in membrane of the carotid body glomus cell activated by decrease in PO2
- Closing on K+ channels
- Depolarization (K+ can’t leave)
- Opening of voltage-gated Ca2+ channels
- Vesicles release ACh and ATP
- Increase AP frequency
How will reducing blood haemoglobin concentration affect the hypoxic ventilatory response
- No change
- Corotid bodies sense partial pressure
- decrease in partial pressure drives O2 into cell - decrease in PO2 = decrease in O2 t cell
Ventilatory Response to CO2/H+
- Increase in arterial PCO2 or decrease in pH lead to increase in ventilation
- Breathing is more sensitive to changes in PCO2 than PO2 in air breathing vertebrates
- Response results from both peripheral and central chemoreceptors
Central CO2/H+ chemoreceptors
- Central Chemoreceptors in the medulla sense CO2 and H+ cerebral spinal fluid, which are related via the carbonic anhydrase reaction
- CO2 can cross the blood-brain barrier, but H+ cannot, so arterial CO2 is also sensed by these receptors
- Central receptors contribute more than peripheral chemoreceptors to the ventilatory response to arterial CO2, but only peripheral chemoreceptors respond to changes in arterial pH
How is a decrease in both PO2 and PCO2 accounted for by alveolar ventilation
At a given PCO2, the greater the PO2 the less ventilation will occur in compensation
- A decrease in pH will shift the curves to the left to increase ventilation at a given PCO2 and PO2 value
How will the hypoxic ventilatory response affect arterial CO2?
- Decreases in PO2 cause subsequent decreases in PCO2
- Increases in PO2 causes increases in PCO2 due to decrease in alveolar ventilation
- Implies a restrained response to hypoxia - can’t exhale too much CO2 (prominent Vasodilator)
