Neural control of breathing Flashcards
What type of muscle is respiratory muscle and what does that mean for the contractile signals?
All respiratory muscle tissues are of the skeletal type, and so require nervous stimulation in order to contract. Contractile signals are initiated within the brain and descend via spinal tracts, which synapse with the lower motor neurons that innervate the respiratory muscle tissue.
What is the central pattern generator (CPG)?
A complex system of neurons within the brainstem (the medulla and pons) which determines the basic pattern of ventilation (i.e. how often to breath and how deep).
What are the roles of chemoreceptors in regulating respiration?
The central pattern generator receives inputs from central and peripheral chemoreceptors (specialised receptors that detect levels of CO2, O2, and pH) and initiates compensatory changes in ventilation.
Where are the Central respiratory chemoreceptors (CRC) located?
Within the medulla (part of the brainstem).
What is the role of the CRC?
Indirectly monitor changes in PaCO2 by responding to changes in the pH of the cerebrospinal fluid (CSF).
How are the CRC activated?
Whilst an increase in PaCO2 will also decrease blood pH, H+ present within arterial blood cannot pass through the blood-brain barrier as they are charged. Therefore CRC do not respond to blood pH directly, however arterial CO2 can pass through the blood-brain barrier into the CSF, where it will then react to produce carbonic acid, and the resulting H+ activates CRCs.
What do peripheral chemo receptors consist of?
They consist of type-I glomus cells present with carotid and aortic bodies.
What is the role of peripheral chemo receptors?
To detect levels of O2, CO2 and pH within arterial blood.
How are peripheral chemo receptors activated?
Peripheral chemoreceptors are activated by low O2, high CO2, and low pH in the blood, and signal to medullar centres to increase ventilation.
Name other types of receptors that the CPG integrates information from.
Stretch receptors within the lungs that prevent damage due to over-inflation
Irritant receptors within the airways that initiate cough.
What is the hypercapnic drive?
Since the level of ventilation is proportional to PaCO2, if PaCO2 increases then ventilation will increase to maintain homeostasis and keep PaCO2 within narrow limits
What is the hypoxic drive?
The increased ventilation in response to decreased PaO2, it only occurs at very low PaO2.
Explain how pathologies affect the initiation of breathing.
Injury, inhibition, or incomplete development of the central nervous system tissue that generate the central respiratory pattern (i.e. the brainstem) will result in dysfunction or cessation of breathing, either temporarily (as occurs in central sleep apnoea) or permanently.
Give 4 examples of pathologies affecting the initiation of breathing.
- Inhibition the brainstem caused by drugs such as opioids and barbiturates
- Injury to the brainstem caused by stroke or trauma
- Congenital defects in brainstem signalling processes (central hypoventilation syndrome, in which individuals lack the capacity to breath whilst asleep)
- Insufficient development of the relevant structures and pathways in neonates (infantile central sleep apnoea)
