Final answer:
The brain is the central control center responsible for regulating all body functions and the spinal cord coordinates reflex actions. Both the brain and spinal cord form the central nervous system, which is the correct answer to what structure controls all functions of the body and is responsible for reflex actions.
Step-by-step explanation:
Which Structure Controls Body Functions and Reflex Actions?
The brain is the central control center of the body that governs virtually all functions, whether voluntary or involuntary. It is a key component of the central nervous system (CNS), which also includes the spinal cord. The brain manages complex mental activities like thought and reasoning, and through the autonomic nervous system, it also regulates involuntary activities such as heart rate, respiration, and digestion. The spinal cord, meanwhile, is responsible for the coordination of reflexes by integrating sensory and motor pathways, allowing for reflex actions without the direct involvement of the brain.
According to the options provided in the question, the structure responsible for controlling all functions and reflex actions would be the central nervous system, which includes both the brain and the spinal cord. Therefore, the correct answer is option 4, the Central Nervous System.