which center stimulates inspiration by increasing the activity of the dorsal respiratory group (drg)
Dorsal respiratory group Inhalation or inspiration, begins when cells of the solitary tract nucleus (along with cells of the ventral respiratory group)[citation needed] begin a steady increase in firing, leading to contraction of the respiratory muscles. When neurons in the DRG are activated they send impulses down the phrenic and intercostal nerves to stimulate the diaphragm and external intercostal muscles. The thoracic cavity expands and air rushes into the lungs due to the negative pressure, producing inspiration. When the cells stop firing, the respiratory muscles relax, inhalation ceases, and exhalation begins.
Muscles of respiration The muscles of respiration are those muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, to a lesser extent, the intercostal muscles drive respiration during quiet breathing. Additional 'accessory muscles of respiration' are typically only used under conditions of high metabolic demand (e.g. exercise) or respiratory dysfunction (e.g. an asthma attack). However, in instances where these accessory muscles become stiff and hard, expansion of the rib cage can be restricted. Maintenance of the elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.