Final answer:
Neurons responsible for the cyclic nature of respiratory-muscle function are located in the brain stem.
Step-by-step explanation:
The neurons responsible for the cyclic nature of respiratory-muscle function are located in the brain stem. The major brain centers involved in controlling pulmonary ventilation are the medulla oblongata and the pontine respiratory group. The medulla oblongata contains the dorsal respiratory group (DRG) and the ventral respiratory group (VRG), which are responsible for maintaining a constant breathing rhythm and controlling forced breathing. The pontine respiratory group consists of the apneustic and pneumotaxic centers, which control the depth and rate of inspiration.