CSB346 Lecture 8 Review Notes

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Cell and Systems Biology
John Peever

CSB346 Lecture 8 Summary – Airway and Pulmonary Reflexes Mechanical control of breathing - The respiratory networks need to know how the respiratory muscles and lungs/airways are functioning by using mechanoreceptors located in the lungs and upper airways - Lower airway (pulmonary) reflexes (e.g., caudal to the larynx) o Lung distension, edema, chemical irritants, CO2, respiratory sensation (e.g., dyspnea) o Vagus nerve relays the signals from the lungs (e.g., pulmonary mechanoreceptors) to the brain (e.g., respiratory rhythm generator)  Superior laryngeal nerve (iSLN) and recurrent laryngeal nerve (RLN) carry nerve afferents from the trachea, larynx, and sub- and supra-laryngeal regions  Pulmonary branches of the intrathoracic vagus nerve carry nerve afferents from the pulmonary receptors in bronchi and terminal bronchi  Most of the cell bodies of pulmonary and airway afferents are located in the nodose ganglion  Most of the axons of vagal afferents terminate in the NTS o Effect of cutting the vagus nerve on phrenic and hypoglossal nerves  Pulmonary stretch receptors generates signals that is carried via the vagus nerve to the brain  Under normal conditions, the pulmonary afferents in the vagus nerve  Regulates breathing  Endogenously suppress phrenic and hypoglossal activity  When the vagus nerve is cut, phrenic and hypoglossal activity is no longer suppressed  Effect is larger on the hypoglossal nerve than it is on the phrenic nerve o Effect of cutting the vagus nerve on HB reflex  HB reflex protects over-inflation of the lungs  Lung inflation = ↑ intratracheal pressure = ↓ respiratory frequency = ↓ blood pressure  Slowly-adapting pulmonary receptors located in the smooth muscle of the large and small intrathoracic airways  When the vagus nerve is cut, there is no HB reflex  The dog tries to breathe normally despite lung inflation = ↑ intratracheal pressure o Types of pulmonary receptors  BPC (unmylinated, C-type fibres)  RAR (mylinated, A-type fibres)  SAR (mylinated, A-type fibres)  Located in smooth muscle of intrathoracic airway  Stimulated by lung inflation  Reflex response o Hering-Breuer reflex  Inspiratory termination  Expiratory prolongation  Airway dilation o Bronchodilation o Tachycardia o Activity of pulmonary receptors  Increased lung volume activates both SAR and RAR  SAR = ↑ firing of AP, but adapts slowly  RAR = ↑ firing of AP, but stops immediately  Both SAR and RAR are active across the respiratory cycle  SAR and RAR fire during inspiration and expiration o Lung inflation (pulmonary stretch receptor)  SAR neuron in nodose ganglion  P-cells in NTS  RRG (PRG, VRG, DRG, RTN)  Prolong expiratory activity of E-Dec neurons  Inhibit inspiratory activity of inspiratory neurons  Inhibit phrenic nerve  Induce HB reflex, which is termination of inspiration and prolongation of expiration  P-cells always fire when the PSR do  Therefore, stretch receptors indirectly control P-cell firing  P-cells send their information to the VRG  Types of respiratory neurons in the VRG o I-Dec, I-All, I-Aug, E-Dec, E-Dec(early), E-Aug  Phrenic nerve
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