I'm currently in an A.S. program for Medical Assisting. CMAs/RMAs are graduates of accredited institutions-- CMAs from CAAHEP, RMAs from ABHES institutions-- who have taken and passed the CMA exam from the AAMA or the RMA exam from the AMT. There are MAs who aren't CMAs-- usually those are the ones with only on-the-job training or from a vocational school. Within the MA/CMA realm, there are 2 categories... Administrative Medical Assistants, and Clinical Medical Assistants. The clinical requires more lab hours on campus, and they are qualified to give injections, run EKGs, perform spirometry tests, check vitals, draw blood, start an IV(though we can't push meds through), etc.... with the STRICT clarification that a DOCTOR must be present in the building with which we are working. We are under his license, and therefore he must be present. THAT is why we can't work in nursing homes, home health, etc-- not always a dr present. That's also why we can't work in hospitals-- we have to receive our orders directly from a doctor. Technically, MAs only work in dr offices for that reason, and our equal partner in hospitals is an LVN/LPN (well, those who are CMAs, anyhow). We can't do catheters, push meds via IV, and several other things. We also get paid WAY LESS than nurses, but the trade off is that we don't have to have wild hours in hospitals, get our own licensing, etc.
CNAs are basically assistants for the nurses.... and they do get the dirty jobs. They typically have less training (some just a couple of weeks!), and they work mostly in hospitals and nursing homes.
MAs sometimes use the MA program as a starting point to get into Physician Assistant school. You get your A.S., get a few more courses in (Microbiology, etc), get your Bachelor's (though that is optional for some PA schools I think), get 2000 or so hours of medical practice hours, then apply to PA/NP school. The only difference between a PA and a Nurse Practitioner is an NP has a nursing background... they even go to the same classes/degree program, but end up with a different set of letters behind their name. That is my ultimate goal-- PA school. I have a B.A. in an unrelated field, and getting my A.S. in Medical Assisting now. After a few years of practice and a few more courses, I intend to apply to UC Davis Med School for the PA program.