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.
Pharynx In humans the pharynx is part of the digestive system and also of the conducting zone of the respiratory system. (The conducting zone also includes the nostrils of the nose, larynx, trachea, bronchi, and bronchioles, and their function is to filter, warm, and moisten air and conduct it into the lungs.[1]) The pharynx makes up the part of the throat situated immediately behind the nasal cavity, behind the mouth and above the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx, the oropharynx and the laryngopharynx. It is also important in vocalization.