control of breathing Flashcards
chemoreceptors
provide feedback on blood PO2, PCO2 and pH.
mechanoreceptors
provide feedback on mechanical status of lungs, chest wall and airways.
brain and control of breathing: neural signals
Sends neural signals to:
- Respiratory muscles to produce rhythmic breathing movements, e.g., diaphragm and intercostals
- Upper airway muscles, e.g., laryngeal, pharyngeal and tongue.
- Produce reflexes to keep airways patent, e.g., cough, sneeze, gag.
peripheral chemoreceptors
small, highly vascularised bodies
in region of aortic arch and carotid sinuses.
Information sent via the glossopharyngeal and vagus nerves to the nucleus in brainstem called NTS.
respond to decrease in PO2 (hypoxia)
peripheral chemoreceptors réponse to hypoxia
- Reduction in arterial PO2
- Peripheral chemoreceptors stimulated.
- Neural signals sent from carotid and aortic bodies to NTS in brainstem.
- Ventilation increases to restore PO2 levels.
ventilatory response to hypoxia
Progressive reductions in inspired oxygen have little effect until about 60 mmHg.
Below 60 mmHg there is a progressive hyperventilation.
Hypoxic response originates in carotid and aortic bodies.
Play little part in the moment to moment control of breathing
central chemoreceptors
clusters of neurones in the brainstem that are activated when PCO2 is increased (hypercapnia) or pH decreased.
central chemoreceptors and hypercapnia
Increase in arterial PCO2
Central
chemoreceptors
(brainstem neurones)
stimulated.
Signals processed and
information passed on to neuronal clusters in brainstem involved in
generating breathing.
- Ventilation increases to restore PCO2 levels.
ventilatory response to hypercapnia
Very small changes in PCO2 have large effects on ventilation (unlike O2).
Hypercapnic response originates in central chemoreceptors in brainstem.
Plays major role in moment to moment control of breathing.
inflation of lungs and mechanoreceptors
Inflation of lungs activates mechanoreceptors.
Neural signals sent via vagus nerve to NTS in brainstem.
Ventilation adjusted accordingly.
integration of information in brainstem
1) NTS - Receives information from
mechanoreceptors and peripheral chemoreceptors.
2) This information is processed in brainstem by respiratory neurones.
3) Cluster of respiratory neurones in brainstem generate rhythm of breathing.
4) The rhythmic signal is sent to the respiratory muscles
respiratory pattern generating neurons in brainstem
Inspiratory neurones:
active during inspiration.
Expiratory neurones: active during expiration.
respiratory rhyme generating neurons in brainstem
Bilateral cluster of neurones with rhythm generating properties.
Continue to produce a respiratory-like rhythmic output when isolated
output from brainstem to respiratory muscles
Brainstem neurones produce rhythmic output.
Rhythmic neural signals sent to spinal cord.
Phrenic nerve exits spinal cord at
cervical spinal cord level 3-5.
Phrenic nerve innervates diaphragm.
Nerves exiting thoracic spinal cord
innervate intercostal muscles.
primary motor cortex and motor control
Breathing is a motor act and like all other motor acts it can be controlled voluntarily.
The neural basis for the voluntary control of a motor action is attributed to the motor cortex.
corticospinal tract, control of breathing
Volitional control of breathing:
Upper motor neurones originate in the primary motor cortex.
Descend as corticospinal tract.
Synapse with lower motor neurones, either directly or indirectly via interneurones, located in the anterior horn of C3, C4 & C5.
Motor neurones project as phrenic nerve to the diaphragm.
