4.2 Neural & Chemical Control of Breathing Flashcards
Phrenic nerves
- Nerve roots – anterior rami of C3, C4 and C5.
- Motor functions – innervates the diaphragm.
- Sensory functions – innervates the central part of the diaphragm, the pericardium and the mediastinal part of the parietal pleura
Inhalation
- When diaphragm contracts - it flattens
- This increases the thoracic cavity volume
- Pressure in thorax is decreased relative to the atmosphere - air moves in
- Active process
- Supported by external intercostals
Expiration
- When diaphragm relaxes - moves upwards
- The chest wall recoils under its own elasticity
- Thorax cavity volume is decreased
- This is a passive process normally - unless forced expiration
- Supported by internal and innermost intercostal muscles
Respiratory Pattern Generator (RPG) location
• Located bilaterally in the brain stem
• The dorsal respiratory group of neurons - dorsal surface of the medulla (RPG)
• The basic rhythm of respiration is set by these dorsal neurons on the medulla sending inspiratory neuron action potentials to spinal nerves innervating the diaphragm and
external intercostal muscles.
• The ventral respiratory neurons - ventral-lateral surface of the medulla
• The pneumotaxic centre of neurons - dorsally on
the pons
Normal respiratory rate
• Approx 12 - 16 breaths per minute
What does the RPG detect?
- pO2
- pCO2
- pH
- Lung stretch (also sent to RPG via vagus nerve - CN X)
Accessory muscles of respiration
- Sternocleidomastoid (CN XI)
- Trapezius (CN XI)
- Pectoralis major
- Scalene
- External intercostals
Intercostals neurovascular supply
• Neurovascular bundle found between internal and innermost intercostal muscles
• From top to bottom:
• Vein
• Artery
• Nerve
(VAN)How do chemo receptors send signals to RPG?
- In the central chemoreceptors PaCO2 and pH changes send signals directly to RPG
- Peripheral chemoreceptors detect changes in PaO2, PaCO2 and pH
- Send signals to the brainstem via Cranial Nerves IX/X
RPG Pathway
- RPG sends signals to the inspiratory (and expiratory neurones) in the brainstem
- Expiratory neurones are not used until forced expiration
- Expiration is normally a passive process
- Both sets of neurones can mutually inhibit each other when active
- This prevents simultaneous activity of inpsiration/expiration
- Inspiratory neurones send signals to diaphragm (via phrenic nerve) and external intercostals
- Expiratory neurones upon forced expiration signal to internal and innermost intercostals
- Intercostal muscles innervated by intercostal nerves (T1-T12)
Voluntary control
- There is also voluntary control of phrenic nerves and intercostal nerves going to external intercostals to allow for inspiration
- Voluntary control arises from the primary motor cortex and allows for altered inspiration e.g. holding your breath
Ondine’s curse
- Can occur following strokes affecting the brainstem
- Where RPG and/or its inspiratory/expiratory connections are destroyed
- Causes loss of involuntary control of breathing
- Only voluntary control of respiratory muscles left
How is stretch of the lung detected?
• The brainstem receives information about how expanded the lungs are from stretch receptors located in the walls of bronchi and bronchioles
• They transmit information via the vagus nerve back to the brainstem and function to prevent over inflation of
the lung
Peripheral chemoreceptors
- Found in glomus cells of carotid bodies
- Located in the bifurcation of common carotid arteries
- Also found in aortic bodies - found in the aortic arch
- Major function of carotid and aortic bodies is to sense hypoxaemia and signal cells in the medulla to increase ventilation
- Along with pO2 they also detect changes in pH and pCO2
