Control of Breathing Flashcards
at rest what is PO2?
13.3 kPa, PCO2 = 5.3 kPa
what is the at rest exchange?
250ml O2/min & ~200ml CO2
what is the walking 3mph exchange?
800ml O2/min & ~750ml/min CO2
what is the severe exercise exchange?
5000ml O2/min & 6000ml CO2/min.
what is breathing monitored by?
vocalisation - signing
emotional events - crying
reflexes - coughing
volitional control - breath holding
physiological challenges - sleep and exercise
how does the brain receive signals about breathing?
chemoreceptors and mechanoreceptors
what information do chemoreceptors send back to the brain?
provide feedback on blood PO2, PCO2 and pH
how do mechanoreceptors send signals to the brain?
provide feedback on mechanical status of lungs, chest wall and airways
where does the brain send signals to about breathing?
-respiratory muscles
-upper airway muscles
-reflexes
what does the brain tell the respiratory muscles to do?
produce rhythmic breathing movements eg, diaphragm and intercostals
which upper airway muscles does the brain send neural signals to about breathing?
laryngeal pharyngeal and tongue
what reflexes can the brain send neural signals to about breathing?
keeps airways patent
e.g. cough, sneeze, gag
what makes up the brain stem?
Many important neuronal cell groups (nuclei) in brainstem with roles in regulation.
what are chemoreceptors?
Chemoreceptors are sensory receptors that detect chemical changes in the surrounding environment.
what do chemoreceptors in the respiratory system do?
detect changes in the PO2, PCO2 and pH in blood
what is hypoxia?
decrease in O2
what is hypercapnia?
increase in CO2
what are peripheral chemoreceptors?
Peripheral chemoreceptors
are small, highly vascularised bodies
in region of aortic arch and carotid sinuses.
how do the peripheral chemoreceptors send information to the brain stem?
Information sent via the glossopharyngeal and vagus nerves to the nucleus in brainstem called NTS.
where are peripheral chemoreceptors found?
regions of the aortic arch and carotid sinus
what do peripheral chemoreceptors respond to?
decreases in PO2 (hypoxia)
what happens when peripheral chemoreceptors are stimulated?
- Neural signals sent from carotid and aortic bodies to NTS in brainstem.
- Ventilation increases to restore PO2 levels.
what effects does progressive reductions in inspired oxygen have?
-little effect until 60mmHg
-below 60mmHg there is a progressive hyperventilation
where does the hypoxic response originate?
in carotid and aortic bodies.
Play little part in the moment to moment control of breathing.
what are central chemoreceptors?
Central chemoreceptors
are clusters of neurones in the brainstem that are activated when PCO2 is increased (hypercapnia) or pH decreased.
when are central chemoreceptors activated?
when PCO2 is increased (hypercapnia) or pH decreased.
what happens when central chemoreceptors are activated?
Signals processed and
information passed on to neuronal clusters in brainstem involved in
generating breathing.
- Ventilation increases to restore PCO2 levels.
what are the ventilatory responses 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
what are mechanoreceptors?
Mechanoreceptors are sensory receptors that detect changes in pressure, movement and touch.
In respiratory system mechanoreceptors detect movement of lung and chest wall.
E.g., during inspiration mechanoreceptors detect inflation of lungs and movement of chest.
how does messages from the mechanoreceptors reach the brain stem?
via the vagus nerve
to the nucleus cactus solitairus in the brainstem
what activates mechanoreceptors?
Inflation of lungs activates mechanoreceptors.
Ventilation adjusted accordingly.
why are mechanosensory signals?
Mechanosensory signals are essential in adapting and adjusting breathing.
Integrating respiratory pattern with other movements, eg., posture, locomotion.
what are the locations of mechanicalreceptors?
airway smooth muscle
airway epithelium
what is the stimulus of mechanoreceptors?
inflation/distension of airways
rapid lung inflation or deflation, or oedema
what are the reflexes of mechanoreceptors?
termination of inspiration
sigh or shortened expiration
where does the NTS receive information?
from
mechanoreceptors and peripheral chemoreceptors
This information is processed in brainstem by respiratory neurones.
how is rhythm of breathing generated?
Cluster of respiratory neurones
The rhythmic signal is sent to the respiratory muscles.
what neurons are active during inspiration?
inspiratory neurons
how do respiratory rhythm generating neurons in the brainstem work?
Bilateral cluster of neurones with rhythm generating properties.
Continue to produce a respiratory-like rhythmic output when isolated.
what neurons are active during expiration?
expiratory neurons
what is the 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.
what is the primary motor cortex and motor control of breathing?
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.
what is the cortical 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.
what is the brainstem control of breathing?
Neural inputs (chemoreceptors & mechanoreceptors.
Higher centre modulation
(volitional &
emotional).
Medullary rhythm generating
neurones & NTS.
Neural outputs.
