Neural Control of Breathing Flashcards
What is breathing?
Breathing is a rhythmic process that maintains O₂ and CO₂ pressure gradients between alveoli and blood
What is the significance of ventilation?
Ventilation is regulated to meet the varying O₂ demand and CO₂ production
ventilation is usually proportional to PaCO₂
What is the effect of increased ventilation?
greater ventilation due to more breathing quicker and deeper = more alveolar air -> atm air so blood takes O₂ from air into tissues and removes CO₂
How often does the body demand O₂?
O₂ demands are always constant - the body adjusts homeostasis of blood gases to meet metabolic demands
How is breathing initiated?
Breathing is initiated by neural activation of respiratory muscles, which provide the movement required for ventilation
What stimulates the respiratory muscles?
As respiratory muscles consist of skeletal muscle, they require neural input to contract
Innervation from motor neurons synapsing from descending spinal tracts provide the contractile signal
C3 - C9 via medulla –> phrenic nerve
T1 - T12 to the intercostals
Which muscles are involved in quiet breathing?
Inspiration: Diaphragm
Expiration; Elastic recoil
Which muscles are involved in Forced ventilation?
Respiratory
Inspiration: External intercostals
Expiration: Elastic recoil, Internal intercostals
Accessory
Inspiration: Pectorals, scalene, stemomastoid
Expiration: Abdominals
How does the diaphragm enable quiet breathing to occur?
Contraction and relaxation of diaphragm creates a force for quiet breathing causing heart contractions and relaxtaions
What is the role of elastic recoil?
Elastic recoil pushes air out
How does forced ventilation occur?
A greater speed/force of breathing requires external intercostals for forced inspiration and internal intercostals for forced expiration
This is due to a positive P(intrapleural)
What are accessory muscles?
Their primary role isn’t ventilation, but aid forced breathing movements e.g.
abdominal muscles
Intercostal muscles
How is the breathing mechanism generated?
The basic breathing pattern is generated by neuronal systems within the brain stem
What is the role of the central pattern generator (CPG)?
The central pattern generator can determine how often and how hard to breathe
How does the CPG regulate breathing?
Signals from various inputs provide feedback which are integrated to regulate breathing
What innervations make up the CPG?
Higher brain centres (cerebral cortex - voluntary control over breathing)
- Other receptors (e.g. pain) and emotional stimuli act
through hypothalamus - Respiratory centres; medulla and pons
- Peripheral chemoreceptors; ↓O₂, ↑CO₂, ↓H⁺
- stretch receptors in lungs
- Central chemoreceptors; ↑CO₂, ↑H⁺
- Irritant receptors
- Receptors in muscles and joints
What is the role of central chemoreceptors?
Respond (indirectly) to changes in arterial PaCO₂
Where are central chemoreceptors found?
In the medulla
How do chemoreceptors indirectly respond to blood pH changes?
Central chemoreceptors respond to changes in [H⁺] within the cerebrospinal fluid
H⁺ doesn’t cross blood brain barrier so receptors don’t directly respond to changes in blood pH (except via CO₂)
What is the function of peripheral chemoreceptors?
Respond to changes in arterial O₂, CO₂ and pH
How are peripheral chemoreceptors activated?
Stimulated by a decrease in PaO₂, increased PaCO₂ and acidemia
Where are peripheral chemoreceptors located in the body?
aortic and carotid bodies
How do peripheral chemoreceptors respond to changes in arterial CO₂ and O₂?
Signal to respiratory centres in the medulla, via sensory nerve fibres to increase ventilation (negative feedback)
How do chemoreceptors produce an appropriate level of breathing?
These chemoreceptors work to figure out the metabolic demands of the body so they can send signals to the brain which integrates the signals to produce an appropriate level of breathing
What is hypoxaemia?
low O₂ - stimulates increased ventilation
What is central sleep apnoea?
Temporary cessation of breathing caused by a dysfunction of breathing initiation processes
What are the potential negative health effects of sleep apnoea?
- tiredness
- CVS complication
- Metabolic dysfunction
What are the potential causes of sleep apnoea?
Stroke
- damages respiratory centres in the brain
Drugs (opioids)
- Suppressing neuronal activity
Central hypoventilation syndrome
- injury / trauma to brain stem
- congenital Ondine’s curse
Altitude
- Cheyene stokes respiration
What is cheyenes-stokes respiration?
Oscillating apnoea and hyperapnoea
- different systems start to over compensate for each
other - Hyperventilation followed by hypoventilation to try
manage changes in partial pressure
