Final answer:
The medullary rhythmicity center includes the dorsal respiratory group (DRG) for maintaining regular breathing rhythms and the ventral respiratory group (VRG) for forced breathing, complemented by the pontine respiratory group for depth and rate regulation.
Step-by-step explanation:
The two groups of neurons that the medullary rhythmicity center includes are the dorsal respiratory group (DRG) and the ventral respiratory group (VRG). The DRG is primarily responsible for establishing a constant breathing rhythm by prompting the contraction of the diaphragm and intercostal muscles to induce inspiration.
When DRG activity halts, these muscles relax, leading to expiration. On the other hand, the VRG manages forced breathing by activating the accessory muscles needed for both forced inspiration and expiration.
Moreover, the medulla oblongata's control over respiration is complemented by the pontine respiratory group in the pons, which includes the apneustic and pneumotaxic centers. These further regulate the depth and rate of breathing.