For medical school, you will need an undergraduate degree in any field with at least a year of general chemistry, a year of organic chemistry, a year of biology, a year of math (calculus and/or statistics) and a year of physics with labs as available (medical schools understand that not all schools will have labs for all courses, but complete as many as you can) for most schools. That will cover most schools, but some will require biochemisty, psychology, and/or writing in addition to the big three. In addition, volunteer work, clinical experience (EMS [EMT-B or EMT-P is generally viewed equally], hospital volunteering, physician shadowing, etc) and research experience is also helpful. Your GPA is much more important than any EMS experience you may gain. The average GPA for first year medical students is over 3.5.
Prior to applying you will need to take the Medical School Admissions Test (MCAT) which has questions on verbal reasoning, physics and general chemistry (physical sciences section), and organic chemisty and biology (biological sciences section). Each of those sections are given a grade based on the average score with a 7 being the average for the people taking the test (note: taking the MCAT does not equal applying. MCAT average=21. Average applicant score=27) with a standard deviation of 2. Hence there is a big difference between scoring a 7 and a 10. A test prep course is recommended. During my graduate school I took a course and my score went up 5 points (29->34).
There are two medical professions in the United States, allopathic medicine and osteopathic medicine. While they are licensed and certified by different boards and their schools are accredited by different organizations, there is no distinction made in the United States between practice rights. They each have their own application system. (in addition to the Texas school application system).