Final answer:
During quiet inspiration, the phrenic nerve activates the diaphragm, and intercostal nerves stimulate the external intercostal muscles, both coordinated by the dorsal respiratory group in the medulla oblongata.
Step-by-step explanation:
During quiet inspiration, which is part of eupnea (normal, quiet breathing), the activity in certain nerves leads to the contraction of specific muscles to facilitate breathing. The phrenic nerve is responsible for stimulating the diaphragm, causing it to contract and move downwards. This increases the volume of the thoracic cavity, thereby lowering the pressure inside the lungs and allowing air to flow in. Additionally, the intercostal nerves innervate the external intercostal muscles, which lift the ribs upwards and outwards, further expanding the chest cavity.
The activity of nerves during quiet inspiration is ultimately controlled by the dorsal respiratory group (DRG) in the medulla oblongata of the brain. The DRG maintains a steady rhythm of breathing by sending impulses that initiate contractions of the diaphragm and intercostal muscles. During rest, autonomic nervous system control, involving both parasympathetic and sympathetic nerves, allows for subtle regulation of breathing without conscious input.