Flashcards in Week 6 RM - Respiratory Control Deck (43):
What areas of the brain compose the respiratory centre?
The medulla oblongata and the pons
What is the basic negative feedback mechanism that controls respiration?
Sensors detect changes in the gases, blood pressure etc
This information is transmitted to the central respiratory controller
It sends a response to an effector (respiratory muscles)
What are the neuron groups found in the medulla?
Dorsal respiratory group (DRG)
Ventral Respiratory group (VRG)
What two centres are found in the Pontine Respiratory Centre?
What is the role of the DRG?
Inspiratory neurons which cause the stimulation of contraction of respiratory muscles
The action of the DRG determines the timing of the respiratory cycle
What are the 4 basic steps involved in normal quiet inspiration?
1. Impulses travel from the DRG
2. The impulse reaches the level of the spinal cord at which it will synapse with a motor neuron cell body
3. This motor neuron will travel along the phrenic/intercostal nerves to the respiratory muscles
4. Contraction of these muscles causes inspiration to occur
What is the role of the pre-botzinger complex?
Thought to stimulate the DRG to send impulses
What is the inspiration ramp signal?
DRG signal to the respiratory muscles responsible for the gradual increased in contraction leading to steady increase in lung volume
How is exhalation achieved in normal quiet breathing?
The DRG signal ceases and inspiration muscles relax. This causes the passive recoil of the lungs to reduce volume and expel air
How can the ramp signal be altered?
It can increase more steeply, leading to a more rapid increase in lung volume
It can also be terminated early, causing shorter, more shallow breaths
What are the four nuclei in the DRG?
What is the role of the nucleus retroambigualis?
Predominantly expiration motor neurons to the excitatory muscles on the opposite side of the body to which it is found in the brain
Usually only aids in forced expiration
What is the role of the nucleus ambiguus?
Dilator functions of the pharynx, larynx and tongue
Role of the nucleus paraambigualis?
Has a role in inspiration, to do with the force of contraction of the inspiratory muscles
What is the role of VRG neurons in normal quiet breathing?
Nothing. Almost totally inactive and do not participate in generating respiratory rhythm
What is the role of the VRG in forced breathing?
The inspiratory centre activates alongside the DRG to increase the lung volume to get extra air into the lungs.
During expiration the exploratory centre of the VRG is stimulated and causes forced expiration
What is the role of the pneumotaxic centre?
Controls the off switch for the DRG respiratory ramp (which limits inspiration)
Stimulation of this leads to decreased tidal volume and increased frequency of breathing
What is the role of the apneustic centre?
Prolongs the inspiratory ramp, leading to a higher tidal volume and lower frequency of breathing
What is cortical control of breathing?
The overriding of the DRG a by the cerebral cortex to give voluntary control over breathing
How does cortical control work?
Neurons from the cerebral cortex bypass medulla and travel directly to synapse with the motor neurons further down in the spinal cord
(Very complex and poorly understood area)
What is Ondine's curse?
Primary alveolar hypo ventilation, where there is a permanent defect in the autonomic respiratory control. Long periods of apnea when awake.
What other peripheral inputs are there to the central respiratory centre (apart from chemoreceptors and baroreceptors)?
Upper respiratory receptors in nose, pharynx and larynx responds to irritants, toxins, temperature (initiate cough, sneeze etc)
Lungs contain stretch receptors which are sensitive to the inflation state of the lungs
What is the Hering-Breuer reflex?
Inhibition of inspiration due to an increased level of lung expansion, limiting over inflation of the lungs (not s very important role)
What is the deflation reflex?
When lung volume decreases to certain level there will be a stimulation of the inspiratory centres in order to re inflate lungs (stimulates DRG)
What are the main drivers of respiratory control?
CO2, O2 and hydrogen ions
Where are central chemoreceptors located?
Separate but very close to the respiratory centre neurons
They are found on the anterior lateral surface of the medulla
Comparatively between peripheral and central chemoreceptors, which has a greater effect on altering respiratory rhythm?
Central receptors exert 85% of the response that the DRG gives, and peripheral contribute 15%
However peripheral chemoreceptors are much faster acting
How are central chemoreceptors triggered?
H+ in the CSF which binds to the receptors
Co2 is the most important factor in this, as it is the driver the contributes to central chemoreceptor response
Why is CO2 the most important driver in central chemoreceptor stimulation?
CO2 can cross the blood brain barrier spend enter the CSF whereas H+ cannot. CO2 forms carbonic acids, dissociates to give of H+'which then triggers the response
Which receptors are more alert to arterial changes in pH?
The peripheral chemoreceptors are the only ones that can sense increased H+ in the blood. Central receptors are unaware of arterial changes in pH
True or false: peripheral chemoreceptors are stimulated directly by CO2?
True: the peripheral chemoreceptors are weakly stimulated directly by CO2
Under what circumstances would oxygen stimulate the respiration centre to increase respiration?
This occurs when oxygen levels decrease to a lower level. The lower the level, the stronger the stimulation.
What effect on does a drop in blood pressure (detected by baroreceptors) have on respiration?
Stimulates the increased rate of respiration
What are lung 'J' receptors?
Sensory neurons juxtaposed with pulmonary capillaries , are stimulated when fluid builds up in the alveoli leading to a feeling of dyspnea
What is Cheynes-Stokes respiration?
Deep breaths followed by progressively shallower breaths, then followed by a pause in breathing altogether
What is happening in the respiratory centre to make Cheynes-stokes breathing occur?
Hyperventilation leads to greatly decreased levels of CO2, which greatly reduced the activity of chemoreceptors, leading to inhibition of the medulla DRG. This leads to progressively decreased rates of respiration, as it is taking the brain is just processing that it has low levels of CO2. The low/absent breathing persists until the brain works out CO2 levels are high again, and takes big gasps to get oxygen in.
Under what conditions does Cheynes stokes breathing occur?
Anything that can slow down the blood transport from the lungs to the brain. Most commonly severe heart failure.
What effect does exercise have on the matching of ventilation to metabolic consumption?
It stays the same. Even in heavy exercise the blood gases remain in stable concentrations and well matched to metabolic consumption.
If blood gases don't change during exercise, what stimulates the increased rates of respiration?
Possibilities include brain sending impulses to the respiratory centres at beginning of exercise to increase ventilation (psychological)
Joint proprioceptors signalling to the brain to increase respiratory rate
What is the point called at which minute ventilation exceeds oxygen concentration called?
Owes point - only occurs during prolonged/intense exercise. Is different depending to the level of fitness
What are the two types of sleep apnea?
Obstructive or central
What is obstructive sleep apnea?
Pharyngeal muscles lose tone and upper airway narrows. Causes air to be blocked from entering lungs. Common in obesity.