Respiratory 8 Flashcards
Which nerves innovate the skeletal muscles of inspiration?
- phrenic nerves
- intercostal nerves
How is ventilation controlled subconsciously, and where does this occur?
Via respiratory centres that reside in the pons and medulla.
What would be the outcome if the spinal cord was severed above C3-C5? Why?
- death
- the spinal cord would have been severed above the origins of the phrenic nerve and therefore there would be no means of breathing.
Would paralysis to the thoracic region affect breathing?
No, as long as the diaphragm is intact.
Describe the action of respiratory centres.
They set an automatic rhythm of breathing through coordinating the firing of smooth and repetitive bursts of action potentials.
Name the four main stimuli that alter respiratory function.
- emotion (via the limbic system)
- voluntary override (via higher centres in the brain)
- mechanosensory input from the thorax (stretch reflex)
- chemical composition of the blood (changes in pH etc)
Which stimulus that alters respiratory function is most significant?
Chemical composition.
What does the ventral respiratory group of neurons innovate?
- tongue
- pharynx
- larynx
- expiratory muscles
What does the dorsal respiratory group of neurons innovate?
- inspiratory muscles
Name the two types of chemoreceptors.
- central
- peripheral
Where are central chemoreceptors found?
The medulla.
Where are peripheral chemoreceptors found?
The carotid and aortic bodies.
Describe the primary ventilatory drive.
The response of central chemoreceptors to hydrogen ion concentration in the CSF around the brain.
What drives the increase in hydrogen ion concentration?
Raised arterial partial pressure of carbon dioxide (hypercapnea)
What would be the response from central chemoreceptors to an increase in hydrogen ion concentration?
An increase in the rate of ventilation to ‘blow off’ more carbon dioxide.
This drives the equilibrium to the left, utilising more hydrogen to form more carbon dioxide.
Describe secondary ventilatory drive.
The response of peripheral chemoreceptors to changes in arterial partial pressure of oxygen and hydrogen ion concentration of the plasma.
What would be the response of peripheral chemoreceptors to a fall in arterial partial pressure of oxygen to 50mmHg?
A stimulation of ventilation.
What effect would a chronic lung disease have on central chemoreceptors?
- ‘blunted’ or desensitised central chemoreceptors
- this occurs if patients have been exposed to high levels of carbon dioxide for a long time.
- it shifts the body to hypoxic drive, where the rate of ventilation is controlled primarily by peripheral chemoreceptors.
What will happen to the ventilation rate if plasma pH increases?
- alkalosis will occur
- ventilation will be inhibited
- hypoventilation will retain carbon dioxide and drive the equilibrium to the right
What will happen to the ventilation rate if plasma pH decreases?
- acidosis will occur
- ventilation will be stimulated
- hyperventilation will blow off carbon dioxide and drive the equilibrium to the left
Can voluntary control over respiration overcome involuntary stimuli?
No.
Involuntary stimuli such as partial pressure of carbon dioxide and hydrogen ion concentration cannot be over-ridden.
Name three common drugs that affect respiratory centres.
- barbiturates
- most gaseous anaesthetics
- nitrous oxide
