Respiratory Control Centres Overview

Respiratory Control Centres

• Medulla oblongata contains the dorsal respiratory group (DRG) which primarily stimulates inspiration and the ventral respiratory group (VRG) which controls both inspiration and expiration.
• Pons contains the pontine respiratory group (PRG), which modulates respiratory rhythm and fine control of breathing.
• Apneustic centre in the pons inhibits stretch receptor input from pulmonary muscles, allowing for larger breaths (increased tidal volume).
• Pneumotaxic centre in the pons inhibits inhibitory signals from the apneustic centre decreasing breath size (decreased tidal volume).

Voluntary Control

• The motor cortex can override involuntary breathing, allowing for voluntary control.
• Forebrain can influence breathing rate and rhythm during voluntary hyperventilation or breath holding.

Chemoreceptor Reflex

• Peripheral chemoreceptors, located in the carotid and aortic bodies, respond to low pO2, high pCO2, and low pH. They send signals via the glossopharyngeal and vagus nerves.
• Central chemoreceptors in the medulla oblongata respond to changes in cerebrospinal fluid pH, specifically high pCO2 and low pH.
• Arterial partial pressure of oxygen (PaO2) is critical for regulation of ventilation, with low oxygen levels stimulating peripheral chemoreceptors to increase respiratory activity.
• Arterial partial pressure of carbon dioxide (PaCO2) is the most important factor in regulating ventilation, with high CO2 levels stimulating both central and peripheral chemoreceptors.
• High pCO2 leads to the production of H+ ions, driving down pH and triggering the respiratory system to expel more CO2 to restore balance.
• Changes in pH are detected by both central and peripheral chemoreceptors.
• Peripheral chemoreceptors respond to changes in pH due to changes in blood buffer systems.
• Central chemoreceptors respond to changes in pH due to changes in cerebrospinal fluid.

Respiratory Control Centers

• Medulla Oblongata contains the Dorsal Respiratory Group (DRG) and Ventral Respiratory Group (VRG), both crucial for respiratory rhythm generation.
• DRG primarily responsible for inspiration, sending constant stimulation to the diaphragm and external intercostal muscles, causing inhalation. Interruption of this stimulation leads to relaxation and exhalation.
• VRG contains both inspiratory and expiratory neurons, responsible for generating respiratory rhythm, and involved in voluntary breathing by stimulating internal intercostal and accessory respiratory muscles (e.g., forced expiration during exercise).

Pontine Respiratory Group (PRG)

• Located in the pons, the PRG modifies and refines respiratory rhythm, working in conjunction with the medullary DRG.
• It receives neural input from the hypothalamus, affecting respiration based on emotions, arousal, and pain.
• Apneustic Center in the pons controls long, slow, deep breaths by inhibiting stretch receptor input from pulmonary muscles, allowing for bigger breaths (increased tidal volume).
• Pneumotaxic Center in the pons governs precise, fine control of breath by inhibiting the apneustic center to decrease breath size (decreased tidal volume).

Voluntary Control

• The motor cortex can override involuntary breathing, allowing for voluntary control.
• The forebrain can influence rate and rhythm of breathing, as seen in voluntary hyperventilation or breath-holding.

Sensory Inputs

• Chemoreceptor Reflex regulates ventilation and has cardiovascular effects.
  • Central Chemoreceptors located in the medulla oblongata detect changes in cerebrospinal fluid and respond to high CO2 and low pH.
  • Peripheral Chemoreceptors located in the carotid and aortic bodies respond to low O2 in arterial blood.
• Arterial Partial Pressure of Oxygen (PaO2): O2 deprivation decreases activity in most nervous tissues, except for peripheral chemoreceptors.
• Arterial Partial Pressure of CO2 (PaCO2): Most important factor in regulating ventilation.
  • PCO2 and H+ are closely linked.
  • Peripheral chemoreceptors rely on blood as a buffer.
  • Central chemoreceptors rely on cerebrospinal fluid (CSF) as a buffer, and respond to significant changes in ECF pH.
• pH: H+ cannot cross the blood-brain barrier.
  • Body relies on peripheral chemoreceptors to regulate pH.
  • Increased frequency and depth of respiration help to increase pH.

Sensory Inputs: Chemoreceptor Reflex

• Peripheral Chemoreceptors: Located in the carotid and aortic bodies, innervated by the glossopharyngeal and vagus nerve.
  • Activated by hypoxia, increased arterial pCO2, decreased pH, and hypoperfusion.
  • Responsible for sensing large changes in blood oxygen levels.
• Central Chemoreceptors: Located in the locus coeruleus (pons), NTS, midline (raphe) of the ventral medulla, and ventrolateral quadrant of medulla.
  • Respond primarily to high pCO2, detected through a fall in pH of the cerebrospinal fluid (CSF).

Stretch Receptor Input

• Hering-Breuer Reflex: Prevents over-inflation of the lungs.
  • Pulmonary Stretch Receptors in the thorax respond to lung inflation.
  • These receptors send afferent sensory neural input to the respiratory center via the vagus nerve.
  • Inhibits inspiratory neurons, stopping inhalation and allowing for exhalation.

Other Sensory Inputs

• Proprioreceptors: Located in intercostal muscles and diaphragm, respond to stretch.
  • Muscle contraction stimulates positive feedback, increasing motor drive to inspiratory muscles, ensuring resistance to inhalation is met with compensatory muscle recruitment.
• Receptors in Muscles and Joints: Signal to the medullary controller, stimulating hyperpnea (increased breathing rate).
• Irritant Receptors: Located in the epithelial cells of the airways, respond to irritants like dry/cold air, smoke, dust, pollen, chemical fumes, and excess mucus.
  • Trigger protective reflexes, like coughing.

This quiz covers the key components of respiratory control, including the roles of the medulla oblongata and pons. It discusses the functions of various respiratory groups, the influence of the motor cortex, and the role of chemoreceptors in breathing regulation. Test your knowledge of how these systems work together to control respiration.