Initiation of breathing Flashcards
What are the 3 CNS respiratory centres involved in the neurogenic initiation?
- Pons : normal breathing
- Medulla : Brainstem is cut below pons but above medulla (Irregular breathing)
- Spinal cord severed (no breathing)
What is the respiratory centre?
What does it consist of?
What are the two respiratory groups it contains?
What is the pnemotaxic centre?
What is the apneustic centre?
Consists of :
- Bilateral groups of neurons that send muscles to respiratory muscles
- Dorsal and Ventral respiratory groups : Medullary rhytmicicty
- Pneumotaxic centre : Feeds into DRG, Limiits inspiration, controls rate and depth of breathing
- The stronger the signal, the shorter the inspiration and faster rate
- Apneustic center : modulates breathing cycle (no abrupt halt in inspiration)
What is the Dorsal respiratory group (DRG) - medulla?
- Extends the length of the medulla to VRG
- Output = to the inspiratory muscle
- Drives movements and timing
- Active during inspiration - repetitive ‘ramped’ bursts of inspiratory neuronal action potentials for 2 secs on ( allows inspiration), then 3 secs off (allows expiration)
- Allows steady increase in lung volume rather than inspiratory gasps
- Neurones are located in the nucleus tractus solitarius (NTS) which is the sensory terminal for the vagus and glossopharyngeal nerves that transmit sensory signals from many different receptors to the respiratory centre (proprioceptors, airways etc).
What is the ventral respiratory group (VRG)- medulla?
- Either side of the medulla and anterior and lateral to the DRG
- Located in the nucleus ambigus and nucleus retroambiguus
- Pre-Botzinger complex - central pattern generator
- Differs from the DRG :
- Some neurones in the VRG cause inspiration and some cause expiration
- No role in the basic rhythmical oscillations
- Inactive in normal, quiet breathing : DRG is active and expiration is passive
- Involved in active breathing e.g. beyond normal ventillation E.g. voluntary forced exhalation
- Activity increases w exercise, dysponea, lung disease, stress
What is central pattern generation?
Complex interaction of > 6 neurones with different firing patterns, concentrated near the pre-Botzinger complex
3 pahses :
- Inspiratory
- Post inspiratory or expiratory phase 1
- Expiratory phase II
- Expiratory and inhibitory neurotransmitters e.g. NMDA and GABA respectively in conjunction with neuromodulators
What are the efferent pathways from the respiratory centres?
- Bulbospinal inspiratory neurones : Nerves descend from the respiratory centre in the anterior part of the lateral column of the spinal cord and terminate in the anterior horn cells of the cervical and thoracic segments
- Phrenic nerves give the motor control to the diaphragm
- formed by rootlets exciting the cervical spine C3-C5
- Two bilateral phrenic nerves supply the diaphragm
- C2-5 keep the diaphragm alive
- Intercostal nerves - exit the thoracic and lumbar spine to provide input to the intercostal and abdominal muscles
- Cranial nerves give motor output to the upper airway dilator muscles
What is the pneumotaxic centre (upper pons)?
- Sends continual inhibitory imuplses to inspiratory centre of the medulla oblongata and finely runes the respiratory rate and breathing pattern by signalling to the DRG
- Signals limit the activity of phrenic nerve and inhibits the apneustic centre
- Decreases the tidal volume which prevents the lungs becoming too full
- IF stimulated more - breathe fast and shallow
- Stimulated less? Inspiratory depth increases
What is the apneustic centre (lower pons)?
- Smooths the breathing cycle integrates inspiratory cutoff
- Excitatory and sends signals for long deep inspiration by stimulating the DRG and VRG to increase rate and tidal volume i.e. delays the off signa;
- Inhibited by stretch receptors at max inspiration or by the pneumotaxic centre
- Overstimulation ? Apneusis (gasping) through exciting inspiratory neurones which prolong inspiration
- Damage? The respiratory cycle is abrupy
