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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