Control of Breathing Flashcards
Why is breathing a unique behaviour?
- It is continuous from birth to death
- It occurs spontaneously - does not need conscious thought unless there is a problem
What is breathing modulated by?
Reflexes - coughing Volitional control - Breath hold Vocalisation - singing Emotional events - crying - Physiological challenges - Sleep, exercise
What must neural control of breathing do?
- Establish autonomic rhythm: breathing happens without conscious thought
- Respond to metabolic demands
- Respond to mechanical changes: change in posture
- Range of episodic non-ventilatory behaviours: speaking, sniffling, eating
What is Eupnea?
Normal rhythmic breathing
What is Dyspnea?
- Being short of breath
- Unpleasant conscious awareness of difficulty breathing
What are respiratory related neurons?
- Array of interconnected neurons
- Fire more action potentials during the respiratory cycle
What are central pattern generators?
- Brainstem (medulla oblongata)
- Independently generate respiratory rhythm
What are respiratory motor neurons?
- Innervate respiratory muscles
- Axons via the phrenic nerve innervate the diaphragm
What does the frequency of respiratory central pattern generators change?
- The strength of drive from central and peripheral receptors
- Change in both depth and frequency of ventilation
What do chemoreceptors provide feedback on in the respiratory system (to the brain)?
On the PO2, PCO2 and pH
What do mechanoreceptors provide feedback on in the respiratory system (to the brain)?
Mechanical status of the lungs, chest wall and airways
What does neural signals sent to respiratory muscles do?
They produce rhythmic breathing movements e.g. diaphragm and intercostals
What does neural signals sent to upper airway muscles do?
e. g. laryngeal, pharyngeal and tongue
- Produce reflexes to keep airways patent (clear, prevent obstruction) e.g. cough, gag, sneeze
What are chemoreceptors?
Sensory receptors that detect chemical changes in the surrounding environment
- In the respiratory system chemoreceptors detect changes in PO2, PCO2 and pH of the blood
- decreases in O2 - hypoxia
- decreases in CO2 - hypercapnia
What are peripheral chemoreceptors?
- Small, highly vascularised bodies in the region of the aortic arch and carotid sinuses
- Information is sent via the glossopharyngeal and vagus nerve to the nucleus in the brain stem (NTS)
What is the name of the nucleus in the brainstem?
Nucleus Tractus Solitarius
What do peripheral chemoreceptors respond to?
Decreases in Po2 - hypoxia
- Reduction in arterial PO2
- Peripheral chemoreceptors stimulated
- Neural signals sent from carotid and aortic bodies to NTS in the brainstem
- Ventilation increases to restore PO2 levels
Below wat arterial PO2 (mmHg) is there progressive hyperventilation?
60 mmHg
The hypotoxic response originates in the carotid and aortic bodies in peripheral chemoreceptors. What do they play little part in?
The moment to moment control of breathing
What are central chemoreceptors?
Clusters of neurons in the brainstem that are activated when PCO2 is increased (hypercapnia) or pH is decreased
What is the process of the function of central chemoreceptors when there is an increase in arterial PCO2?
- Central chemoreceptors are stimulated
- Signals processed and information is passed on to neuronal clusters in the brainstem involved in generating breathing
- Ventilation increases to restore PCO2 levels
What effect does very small changes in PCO2 have on ventilation?
Large effects
Where do hypercapnic responses originate and what major roles do they play?
- Originate in central chemoreceptors in the brainstem
- Plays major role in moment to moment control of breathing
What are mechanoreceptors?
- Sensory receptors that detect changes in pressure, movement and touch
- In the respiratory system mechanoreceptors detect movement of the lungs and chest wall
e. g. during inspiration mechanoreceptors detect inflation of lungs and movement of the chest
Inflation of the lungs activated mechanoreceptors. What nerve are neural signals sent to the NTS in the brainstem via and what is the result of this?
- Signals sent via vagus nerve
- Ventilation is adjusted accordingly
What are mechanosensory signals essential in doing?
- Adapting and adjusting breathing
- Integrating respiratory pattern with their movements e.g. posture and locomotion
Where does the NTS in the brainstem receive information from?
- Mechanoreceptors and peripheral chemoreceptors
- This information is processed in the brainstem by respiratory neurons
What cluster of respiratory neurons in the brainstem generate the rhythm of breathing?
- Central pattern generator neurons
- The rhythmic signal is sent to the respiratory muscles
When are inspiratory neurons active?
During inspiration
When are expiratory neurons active?
During expiration
Rhythm generating neurons are a bilateral cluster of neurones found on both sides of the brain-stem. What kind of properties do they have?
Rhythm generating properties
Where does the phrenic nerve exit the spinal cord and what does it innervate?
- Exits at cervical spinal cord at level 3-5
- Innervates the diaphragm
What do nerves exiting the thoracic spinal cord innervate in relation to respiration?
Innervates intercostal muscles (a group of muscles found between the ribs which are responsible for helping form and maintain the cavity produced by the ribs, and assisting with the expansion and contraction during breathing
What are the functions of the dorsal respiratory group and where are the found?
- Found in and around NTS
- Are mainly inspiratory neurons
- Receives sensory info: chemoreceptors and mechanoreceptors via CNXI and CNX
- Integration of sensory info from the respiratory system
What are the functions of the ventral respiratory group?
- Both inspiratory and expiratory neurons
- Contains motor neurons
- Contains regions which may be the respiratory Central pattern generators
What is the function of pontine respiratory group?
Modulates respiratory output
Where is volitional and emotional modulation of breathing found?
Higher centres in the brain stem
What is a homunculus?
The distorted figure of a human superimposed on an illustration of the surface of the brain; used to demonstrate those portions of the body supplied by the various motor and sensory cortical regions
What are the voluntary actions that alter airflow?
- Breath holding
- Speaking
- Singing
*control is precise and not absolute (breath holding is overridden by ventilatory drive from chemoreceptors)
Where do the voluntary actions that alter airflow originate in?
The cerebral cortex
What are the 2 main mechanisms for motor control from the cerebral cortex?
- Cortical neurons send axons to the brainstem
- Cortical premotor neurons send axons to motor neurons which control the muscles of respiration
What do chemoreceptors detect?
Changes in PO2, PCO2 and pH in blood, send neural signals to NTS
What do mechanoreceptors detect?
Mechanical changes in lung and chest wall, send neural signals to NTS
Where are respiratory rhythm generating neurons located?
In the brainstem
