Week 2 Control of Ventilation ✅ Flashcards
Where do the automatic impulses for breathing come from?
Brainstem - pons and medulla
What structure can override automatic impulses for breathing for voluntary control?
The cerebral cortex
What injury to the spinal cord stops breathing?
If spinal cord transected above origin of phrenic nerves
What 2 neuro mechanisms regulate breathing?
Voluntary control
Automatic control
How does the voluntary control of breathing work?
Sends impulses to respiratory motor neurones via corticospinal tracts
How does the automatic process of breathing work?
Outflow from pons and medulla to respiratory motor neurones is located in lateral and ventral portions of spinal cord
What is the respiratory centre made up of?
Several groups of neurons located bilaterally in medulla oblongata and pons of brainstem
What are the 3 main collections of neurones in the respiratory centre? Where are they based and what do they do?
Dorsal respiratory group - located in dorsal portion of medulla - responsible for inspiration
Ventral respiratory group - located in ventral lateral portion of medulla - responsible for expiration
Pontine respiratory group - located in pons - pneumotaxic centre and apneustic centre
What does the pneumotaxic centre do?
Assists with switching off inspiration and involved in respiratory rate and volume
What does the apneustic centre do?
Excitatory effect on inspiration
What is the ramp signal?
Nervous signal to diaphragm is weak but then ramps up steadily over 2 seconds then ceases abruptly for 3 seconds which turns off excitation of diaphragm and allows elastic recoil etc
What is the benefit of ramp signal?
Steady increase of volume into lungs rather than inspiratory gasps
The sooner the ramp ceases, the shorter the…?
Duration of inspiration AND duration of expiration
Which centre switches off ramp signal and therefore controls the duration of the filling phase in the lung cycle?
Pneumotaxic
What happens when the pneumotaxic signal is strong?
Inspiration can be little as 0.5s and fill lungs only slightly
What happens when the pneumotaxic signal is weak?
Inspiration can continue for 5s+ and allowing filling of lungs with excessive air
Which centre controls rate of breathing?
Pneumotaxic
Normal quiet breathing comes from which group?
Dorsal respiratory group
Does the ventral respiratory group help control inspiration or expiration?
Both!
What does the ventral respiratory group during heavy expiration?
Stimulate abdominal accessory muscles
When does ventral respiratory group act?
When high levels of pulmonary ventilation required e.g. during heavy exercise
Where are central chemoreceptors located?
Near ventral surface of medulla, in vicinity of exit of 9th and 10th nerves
What are the central chemoreceptors surrounded by?
Brain ECF
What do central chemoreceptors respond to?
Changes in H+ concentration in ECF
What does an increase in H+ in ECF do?
Stimulates increase in ventilation
What does a decrease of H+ in ECF do?
Inhibits ventilation
What controls composition of ECF around central chemoreceptors?
CSF, local blood flow and local metabolism
What separates CSF from blood?
Blood brain barrier
Is the blood brain barrier impermeable or permeable to H+ and HCO3- ions?
Impermeable
Is the blood brain barrier impermeable or permeable to CO2?
Permeable - can diffuse across easily
What happens when blood PCO2 rises?
Diffuses into CSF from cerebral blood vessels, liberates H+ which stimulates the chemoreceptors
How does CO2 levels regulate ventilation?
Affect of pH of CSF
Increased arterial PCO2 - does this cause cerebral vasodilation or vasoconstriction? Why?
Vasodilation - enhances diffusion of CO2 into CSF and ECF
What is the normal pH of CSF?
7.3-7.4
Where are peripheral chemoreceptors located?
In carotids at bifurcation of the common carotid arteries
In aortic bodies above and below the aortic arch
Are central chemoreceptors also sensitive to PO2 of blood?
No
What are peripheral chemoreceptors good for?
Detecting oxygen changes in the blood and can respond to changes of CO2 and H+ concentration to a lesser extent
What arterial changes can peripheral chemoreceptors respond to?
PO2
PCO2
H+
Do peripheral chemoreceptors respond to PO2 or oxygen concentration?
PO2
Is the response to peripheral chemoreceptors rapid or gradual?
Rapid
What is the potential effect of hypoxaemia with absence of peripheral chemoreceptors?
What condition with complete absence of hypoxic ventilatory drive can you see this effect?
Depress ventilation through direct effect on respiratory centres?
Bilateral carotid body resection
What can be an effect of chronic hypoxia?
Hypertrophy of carotid bodies
Which is more important - central or peripheral chemoreceptors?
Central, however peripheral is more rapid
What do CAROTID peripheral chemoreceptors respond to?
Fall in arterial pH - regardless of respiratory or metabolic
What is the mechanism of central control modified by peripheral chemoreceptors?
- Increased PCO2/decreased PO2
- Chemoreceptors (carotid body)
- Respiratory control centre
- Respiratory muscles
- Increased frequency and depth of breathing
What is the Hering-Breuer inflation reflex?
Pulmonary stretch receptors discharge in response to distension in lung - stimulation of these slows respiratory frequency (self-regulatory negative feedback)
I.e. inflation of lungs inhibits further inspiratory muscle activity and deflation of lungs initiates inspiratory activity
What are irritant receptors and where do they lie?
They respond to irritants and lie between epithelial cells
How do irritant receptors work?
Stimulated - impulses travel up vagus nerve via large myelinated fibres
Causes bronchoconstriction and hypernea
Give 3 examples of when hypernea might occur
Coughing, sneezing, exercise
What conditions might irritant receptors cause bronchoconstriction?
Asthma and emphysema
What are J receptors? What are the features?
(Juxtacapillary)
Endings of non-myelinated C fibres
In the alveolar walls close to capillaries
Respond quickly to chemicals injected into pulmonary circulation
Impulses pass up vagus nerve slow conducting non myelinated fibres and result in rapid shallow breathing
Involved in difficulty of breathing with left heart failure and interstitial lung disease
Stimulated by pulmonary capillaries engorged with blood or pulmonary oedema
