The government of the Roman Empire changes significantly from that of the Republic.
While most of the linked offices (or magistracies) taken from the time of the Emperor Trajan, are the same or similar to that of the Republic, the real power lay with the Emperor (princeps) himself.
The senate, the elite class of Rome, functioned more as a club of the rich and famous families than necessarily as a governing body in the Imperial system.
Many of the offices listed here were filled by members of the senate, or in a similar capacity to how they had always been filled, and inclusion in the Senate was still an indication of great status despite their reduction as true law-makers.
These positions, mostly appointments rather than elections, are still the basis for the governing class, and performed the duties listed, within the agenda of the Emperor.
It is important to note that despite the conversion from Republic to veiled monarchy and the creation of imperial heirarchy, freedman advisors, etc., the institutions of the Republic remained for centuries.
Additional information regarding the offices in the Republican period is available at the Birth of the Roman Republic page.
Did you know...?
Cicero is an example of how a senator can progress up the cursus honorum to achieve the highest office.