Respiratory System and Breathing Control

Overview

• Breathing is primarily an involuntary and automatic process.
• Main function: Supply oxygen to the body and remove carbon dioxide.
  • Breathing rate and depth generally regulated by carbon dioxide and oxygen needs.

Physiological Process

• Exercise increases oxygen demand, accelerating breathing automatically.
• Receptors in the body feed metabolic state information to the respiratory center in the brainstem.
  • Adjusts the firing pattern of inspiratory and expiratory neurons.
  • Inspiratory neurons activate during inspiration.
  • Expiratory neurons activate during deep expiration (quiet expiration is passive).
• Neurons synapse with motor neurons in the cervical and thoracic spine.
  • Motor neurons travel to respiratory muscles, adjusting contraction patterns.

Nervous System Involvement

• Phrenic nerves control the diaphragm.
• Intercostal nerves innervate intercostal muscles.

Respiratory Center

• Located in the medulla with primary areas:
  • Dorsal Respiratory Group (DRG): Associated with inspiration.
  • Ventral Respiratory Group (VRG): Concerned with expiration.
  • Pre-Bötzinger complex: Potential intrinsic rhythm generator.

Communication with the Pons

• Pneumotaxic center: Inhibits inspiration.
• Apneustic center: Stimulates inspiration.

Regulation of Breathing

• Carbon dioxide concentration is the key regulator of breathing rate.
  • Influences pH changes detected by chemoreceptors.

Chemoreceptors

• Central chemoreceptors: Located on the surface of the medulla, monitor pH in cerebrospinal fluid.
• Peripheral chemoreceptors:
  • Found in aortic and carotid bodies.
  • Respond to pH, carbon dioxide, and oxygen levels.
  • Signal respiratory center via vagus and glossopharyngeal nerves.

Reflexes and Responses

• Increase in carbon dioxide decreases pH, prompting deeper, faster breathing.
• Mechanoreceptors in lungs send mechanical status to respiratory center via vagus nerve.
  • Pulmonary stretch receptors: Trigger inflation reflex to stop inspiration and prolong expiration.

Defensive Reflexes

• Respond to inhaled irritants causing bronchoconstriction or coughing.

Influence of Emotions and Volition

• Limbic system and hypothalamus:
  • Affect breathing through pain and emotional state (e.g., gasping, crying).
• Voluntary control possible (e.g., singing, playing instruments, holding breath).
  • Originates from the primary motor cortex, bypassing the brainstem.
  • Training can increase voluntary control limits.