Final answer:
The major autonomic nerve controlling the body's automatic functions is called the autonomic nervous system (ANS).
Step-by-step explanation:
The major autonomic nerve controlling the body's automatic functions is called the autonomic nervous system (ANS). The ANS serves as the relay between the central nervous system (CNS) and the internal organs, controlling functions such as heart rate, smooth muscle contraction, and glandular activity. It consists of two divisions, the sympathetic nervous system and the parasympathetic nervous system, which often have opposing effects.