Education & training. A crna usually works under the supervision of a physician. Crnas obtain a bachelors degree in nursing, work 1 year in an ICU setting, then go to crna school for 2 years. An anesthesiologist is a physician (md) who completes a bachelor's degree with medical prerequisites, 4 year medical school, 1 year internship, and a 3 year anesthesiology residency. Some complete fellowships in a subspecialty.
MD/Nurse. Anesthesiologist is a medical doctor trained in anesthesiology and a crna is a "registered nurse anesthetist". The md training is much more comprehensive and generally encompasses not only the broad aspects of general medicine and surgery but a more in depth knowledge of anesthetic principles. Crna's, mind you, also undergo rigorous training and testing, and in most situations, you will be taken.