L22 Neural control of ventilation in health and disease Flashcards
What are the spinal origins of the respiratory motor neurones for 3 muscle groups
Diaphragm: Phrenic nerve C3-5
Intercostals (ext: insp, int: exp): T1-L1
Abdominal (rectus abdominus: exp): T7-L1
What are the 3 parts of the Respiratory neuronal network
- Pontine respiratory group: pneumotaxic, apneustic
In the Medulla oblongata, - Dorsal respiratory group/ DRColumn with NTS
- Ventral respiratory group/ VRColumn with Nucleus ambiguus : respiratory rhythm generator- oscillator model
What are 3 critical areas of the pontomedullary regions for respiration, their function and the affect of the vagus nerve on them
Pons (rostral–>caudal)
1. Pneumotaxic centre: essential for normal breathing pattern. With Vagus nerve intact, breathing is shallower and faster compared to cut–> removal w cut vagus nerve = apneustic breathing.
2.Apneustic centre: breathing has prolonged inspiratory phase. However intact Vagus nerve= larger amplitude and slower duration of normal breath pattern due to feedback from afferent stretch receptors in the lungs.
- Medullary region rhythm generator (VRG and DRG)
responsible for gasping–> removal = no breathing. Unaffected by vagus nerve
What are the steps and purpose of the Hering-breuer reflex
- Pulmonary stretch receptors (Large A vagal mechanosensory fibres) in airway smooth muscle are activated on inflation of the lungs
- Vagal afferents (with cell bodies in nodose ganglia) send signal to NTS (DRG) then Pons, then VRG
- Inhibition of inspiratory neurones to diaphragm from VRG switches off inspiration
Purpose is to switch off inspiration and start expiration- it can also make tachycardia and vasodilation
What are the steps and purpose of the cough reflex
- Vagal afferents (small a and C fibres) found in the larynx, trachea and bronchi are stimulated by particulates (mechanosensory) inflammation and gastric reflux (chemosensory)
- Got to Dorsal and Ventral respiratory columns
- Cranial and spinal motor outflow: a)inspiration, b)compression= internal intercostals, abdominal muscles contract but glottis is closed
c) expulsion= glottis opens to allow removal, sphincters close during this period
What is the oscillator model for respiratory rhythm generator and where
The VRG has inspiratory neurones which only stimulate insp muscles and expiratory neurones which only stimulate exp muscles.
These two neurones are connected by inhibitory synapses so when one produces AP they will stimulate muscle and inhibit the other from stimulation therefore never fire at same time.
Why is breathing a 3 phase rhythm not two
- The diaphragms electrical activity rises in inspiration. And opening of the glottis
- Diaphragm has slow declining activity in Post insp relaxation- first half of expiration
Contraction of the diaphragm during exhalation slows down the airflow and allows time for gas exchange. There is also little narrowing of the glottis to increase airway resistance and therefore reduce expiratory outflow
- No activity in exp pause phase at second half of expiration.
What innervates the glottis- valve of respiration- closes off the upper airway
The recurrent laryngeal nerve
Abductor motorneurons: open the glottis
Adductor mns: narrow the opening of the vocal folds.