Reflex actions, which are automatic and rapid responses to stimuli, are primarily controlled by the spinal cord. When a stimulus is detected by sensory receptors in the body, such as touching a hot object, the sensory information is quickly sent to the spinal cord. In response, the spinal cord initiates an immediate reflex action, such as pulling the hand away from the hot object. This rapid response is possible because the sensory information does not need to travel all the way to the brain for processing and then back to the muscles. Instead, the spinal cord acts as a relay station, quickly coordinating the reflex action. While the brain also plays a role in reflex actions, such as modulating the intensity of the reflex, it is not directly responsible for controlling the reflex actions themselves. So, option 2 - the spinal cord - is the correct answer.