Output from higher brain centers can bypass both the drg and vrg and go directly to which controls the accessory muscles of respiration.

These higher brain centers (i.e. output from the cerebral cortex or the basal ganglia) can bypass the dorsal root ganglion or DRG and the ventral respiratory group or VRG because they have different neural pathways and can synapse directly in spinal integration centers that controls the accessory muscles for respiration.

That is true tge cactus as a structural adaptation to its envirinment has it leaves reduced to spines. but this doesnt mean it cant produce food it produces food because of the presence of chlorophyll in its stem