Respiration Control of Breathing Flashcards
What are the values for PO2 and PCO2 at rest?
PO2 = 100 ± 2 mmHg PCO2 = 40 ± 2 mmHg
What is the O2 and CO2 exchange at rest?
~250ml O2/min in, ~200ml CO2/min out
What is the O2 and CO2 exchange during moderate exercise (walking at 3mph)?
~800ml O2/min in, ~750ml CO2/min out
What is the O2 and CO2 exchange during severe exercise?
~5,000ml O2/min in, ~6,000ml CO2/min out
Which factors can modulate breathing?
- Reflexes: coughing
- Volitional control: breath holding
- Emotional events: crying
- Vocalisation: singing
- Physiological challenges: sleep, exercise
Neuronal control of breathing must:
- Establish automatic rhythm (breathing happens without conscious thought)
- Respond to metabolic demands (PO2, PCO2, pH)
- Respond to mechanical changes (change in posture)
- Occur through a range of episodic non-ventilatory behaviours (speaking, sniffing, eating)
What is eupnea?
Normal rhythmic breathing
What is dyspnea?
- Being short of breath
- Unpleasant conscious awareness of difficulty breathing
When might dyspnea occur?
- Changes in arterial PO2 and PCO2 (breath holding, asphyxia, pulmonary disease)
- Normal arterial PO2 and PCO2 (increased airway resistance, exercise, panic attacks)
What is sleep apnea?
People stop breathing during sleep
What are respiratory related neurons (RRNs)?
- Array of interconnected neurons
- Fire more action potentials during respiratory cycle
What are central pattern generators (CPGs)?
- Brainstem (medulla)
- Independently generate respiratory rhythm
What are respiratory motor neurons?
- Innervate respiratory muscles
- Axons via the phrenic nerve innervate the diaphragm
What is the role of chemoreceptors in control of breathing?
- Brain receives neural signals from chemoreceptors
- Chemoreceptors provide feedback on blood PO2, PCO2 and pH
What is the role of mechanoreceptors in control of breathing?
- Brain receives neural signals from mechanoreceptors
- Mechanoreceptors provide feedback on mechanical status of lungs, chest wall and airways
Once the brain integrates neural signals from chemoreceptors and mechanoreceptors, where does the brain send neural signals to?
- Respiratory muscles (to produce rhythmic breathing movements e.g. diaphragm and intercostals)
- Upper airways muscles e.g. laryngeal, pharyngeal and tongue
- Produces reflexes to keep airways patent e.g. cough, sneeze, gag
What is the role of the brainstem in breathing?
- Regulatory role
- Neurons that are involved in the control of breathing are located in the brainstem (medulla of brainstem is particularly important)
What is hypoxia?
Decreases in PO2
What is hypercapnia?
Increases in PCO2
Where are peripheral chemoreceptors located?
Aortic arch and carotid sinus
Same location as the baroreceptors
What are chemoreceptors?
Sensory nerve endings
Small vascularised bodies
Which nerves do the peripheral chemoreceptors send information via?
Glossopharyngeal (IX)
Vagus (X)
Where is information from the chemoreceptors relayed to?
Nucleus tractus solitarius (NTS) in the brainstem
Describe the chain of events that occurs when chemoreceptors detect a decrease in PO2
- Reduction in arterial PO2
- Peripheral chemoreceptors stimulated
- Neural signals sent from carotid and aortic bodies to NTS in brainstem
- Ventilation increases to restore PO2
What effect do progressive reductions in inspired O2 have on ventilation
Very little effect until PO2 = 60 mmHg
Below 60 mmHg, there is progressive hyperventilation
Which region do hypoxic responses originate from?
Carotid and aortic bodies (peripheral chemoreceptors located here)
What role does oxygen play in the moment to moment control of breathing?
Oxygen plays little part in the moment to moment control of breathing, unless levels deplete drastically
Where are central chemoreceptors located?
Brainstem
When PCO2 is increased (hypercapnia) or pH decreased, which neurons are activated?
Central chemoreceptors in the brainstem
What is the chain of events that occurs when PCO2 is increased?
- Increase in arterial PCO2
- Central chemoreceptors (brainstem neurons) simulated
- Signals processed and information passed on to neuronal clusters in the brainstem involved in generating breathing
- Ventilation increased to restore PCO2
Describe the effects of PCO2 on ventilation
Very small changes in PCO2 have large effects on ventilation (unlike O2)
Where do hypercapnic responses originate?
In central chemoreceptors in the brainstem
Which of the following plays a major role in moment to moment control of breathing: PO2 or PCO2
PCO2
What are mechanoreceptors?
Mechanoreceptors are sensory receptors that detect changes in pressure, movement and touch
What do mechanoreceptors do in the respiratory system?
In respiratory system, mechanoreceptors detect movement of lung and chest wall e.g. in inspiration, mechanoreceptors detect inflation of lungs and movement of chest. Can terminate inspiratory effort/prevent overinflation. Adjust ventilation for changes in posture
Which receptors are activated by the inflation of the lungs?
Mechanoreceptors - detect stretch in lungs
Mechanoreceptors are activated by the inflation of the lungs. Neural signals are sent via the _____ nerve to the ___ in the ________.
Vagus nerve
NTS
Brainstem
Mechanoreceptor signals are essential for what?
Adapting and adjusting breathing
Integrating respiratory pattern with other movements e.g. posture, locomotion
Where are mechanoreceptors located?
Airway smooth muscle (stimulated by inflation/distension of airways. Reflex = termination of inspiration)
Airway epithelium (stimulated by rapid lung inflation or deflation. Reflex = sigh)
Describe the ‘termination of inspiration’ reflex
- Mechanoreceptors located in airway smooth muscle are stimulated by inflation/distension of airways
- Reflex = termination of inspiration
Describe the ‘sigh’ reflex
- Mechanoreceptors located in the airway epithelium are stimulated by rapid lung inflation or deflation
- Reflex = sigh
Where do mechanoreceptors and peripheral chemoreceptors send information to?
NTS via vagus nerve
After information is transmitted to NTS from mechanoreceptors and peripheral chemoreceptors, where is information passed on?
To respiratory neurons elsewhere in the brainstem
What are pattern generating neurons?
- Mixed cluster of neurons. Some fire during inspiration, some fire during expiration.
- Activity is modulated based on information coming from the NTS
- Generate breathing pattern
What are rhythm generating neurons?
- Bilateral cluster of neurons with rhythm generating properties
- Fire rhythmically from birth til death
- Pattern can be modulated by pattern generating neurons
Describe how output from the brainstem innervates respiratory muscles (which nerves)
- Brainstem neurons produce rhythmic output
- Rhythmic neural signals sent to spinal cord
- Phrenic nerve exits spinal cord at C 3-5 (cervical spinal cord level)
- Phrenic nerve innervates the diaphragm
- Nerves exiting thoracic spinal cord innervates the intercostal muscles
What is the ‘dorsal respiratory group’, where is it located and what is its function?
- In around the nucleus tractus solitarii (NTS)
- Mainly inspiratory neurons
- Receive sensory information: chemoreceptors/mechanoreceptors (CN IX and X)
- Integration of sensory information from inspiratory system
What is the ‘ventral respiratory group’?
- Both inspiratory and expiratory neurons
- Contains motor neurons (unlike DRG)
- Contains regions which may be respiratory CPG
What does the pontine respiratory group do?
Modulate respiratory output
Which voluntary actions can alter airflow?
- Breath holding
- Speaking
- Singing
Breath holding, speaking and singing are voluntary actions that can alter airflow. Where in the brain do these actions originate?
The cerebral cortex (motor cortex)
What can breath holding be overridden by?
Ventilatory drive from chemoreceptors
What role does the cerebral cortex play in breathing?
Higher centre modulation (volitional and emotional)
Control is precise (e.g. talking) and not absolute (e.g. breath holding can be overridden by ventilatory drive from chemoreceptors)
What do peripheral chemoreceptors detect?
Changes in PO2, PCO2 and pH in the blood
Send signals to NTS
What do mechanoreceptors detect?
Changes in lung and chest all, send neural signals to NTS
Where are respiratory generating neurons located?
Brainstem
Where do respiratory neurons send neural signals to?
Respiratory muscles to produce rhythmic breathing
