Control of Breathing (B2: W7) Flashcards
Where is the “central controller” for respiration?
- Brainstem
- Cortex - voluntary control
- Limbic system, hypothalamus
- Lesser degree
- E.g. fear and rage
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Where are the respiratory centers in the breainstem?
In the pons and medulla
- Poorly defined collection of neurons rather than discrete nuclei
- 3 main groups of neurons
- Medullary respiration center (main headquarters)
- Apneustic center
- Pneumotaxic center
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What two regions of the medullary response center are overlapping, and what is each responsible for?
Dorsal respiratory group = inspiration
Ventral respiratory group = expiration
DIVE
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What is the organization of the medullary respiratory center?
Reticular formation below the 4th ventricle
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Where is the pre-Botzinger complex, and what is it responsible for?
Medullary respiratory center
- Intrinsic respiratory rhythm generator (liken to SA node)
- Mechanism unknown
- Caudal to Botzinger complex
- Rostral to the ventral respiratory group
- Located in the reostral ventrolateral medulla (RVLM)
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How do pre-Botzinger complex nuclei affect inspiration?
- Starts with a latent period
- Crecendo of action potentials
- Causes stronger inspiratory muscle activity (ramp-type pattern)
- Action potentials then cease
- Inspiratory muscle tone falls to pre-inspiratory level
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What is the motor nucleus of CN IX and CN X, and what are the implications if it is destroyed?
Nucleus ambiguus
- If destroyed, there is complete respiratory failure
How does the pneumotaxic center (dorsal) affect inspiration?
Input from the pneumotaxic center shortens breathing
- Breathing rate increases
- Breathing rate is also modulated by glossopharyngeal and vagal nerves
- Terminate in the tractus solitarus, close to the inspiratory center
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Where do afferent signals from airways, lungs, heart, and peripheral chemoreceptors terminate?
CN IX and CN X
- Glossopharyngeal and vagal
- These nerves go into tractus solitarus
- Part of the medulla
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Describe the expiratory area during normal breathing
- Quiescent during normal quiet breathing
- Ventilation in this state is achieved by active contraction of inspiratory muscles (mainly diaphragm)
- Followed by passive relaxation of the chest wall
- More forceful breathing: increased activity of expiratory cells
What happens in animals if there is a transection above the apneustic center (lower pons)?
Affects breathing patterns
- Expiramental sectioning leads to prolonged inspiratory gasps (apneuses)
- Interrupted by transient expiratory efforts
- Apneuses are seen in severe breain injury
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What effect do impulses from the apneustic center have on inspiration?
Excitatory effect on the inspiratory center of the medulla
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What is the role of the pneumotaxic center (upper pons) on inspiration?
- Inhibits inspiration and controls inspiratory volume
- Involved in fine tuning of respiratory rhythm
- If ablated, normal respiratory rhythm intact
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What effect does a transection of the pneumotaxic center have on breathing?
Irregular rate or depth of breathing
- Gasping, ataxic, or both
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What areas are damaged, causing transient vs. permanent apnea?
- Transient apnea: lesion in the temporal lobe
- Permament apnea: lower pons and medulla (around nucleus ambiguus)
What causes central neurogenic hyperventilation?
Medial reticular formation
What is Ondine’s curse and what causes it?
Loss of automaticity
- When you fall asleep, you lose the ability to breathe on your own
- Medial reticular formation or anterolateral C2 (reticulospinal pathway from cordotomy)
Describe Cheyne-Stokes respirations
- 10-20 second periods of apnea followed by equal periods of hyperpnea
- Seen with high altitude, severe heart disease, or sever neurological injury
- Unstable feedback in respiratory control system
- Overblow the PCO2 so that it is too low, then breathing has to stop (apnea) to bring it back up
- Then PCO2 will be too high, and rapid breathing returns
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How does the cortex influence breathing?
Cortex can override the function of the breainstem within limits
- Voluntary hyperventilation can halve the PCO2 to the point of muscular tetany
- Will increase pH by 0.2
- Voluntary hypoventilation is more difficult
- Influenced by PCO2 and PO2
What sensors in the body affect drive of breathing?
- Central chemorecptors
- Peripheral chemoreceptors
- Lung receptors
- Other receptors
Where are the central chemoreceptors located?
- Rostral zone
- Lateral to pyramids
- Medial to CN VII to X rootlets
- Caudal zone
- Lateral to pyramids
- Medial to CN XII rootlet
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What changes are central chemoreceptors responsive to?
- Respond to change in H+ concentration
- Increase in [H+] stimulates ventilation, and vice versa
- Composition of the extracellular fluid is managed by CSF, local blood flow, and local metabolism