Which part of the brain controls involuntary actions such as breathing?

The brainstem is crucial for controlling involuntary actions in the body, particularly those related to maintaining vital functions. It consists of three main parts: the midbrain, pons, and medulla oblongata. Among these, the medulla oblongata plays a key role in regulating essential autonomic functions such as breathing, heart rate, and blood pressure. By constantly monitoring the levels of carbon dioxide and oxygen in the blood, the brainstem adjusts the rate and depth of breathing accordingly, ensuring that the body maintains homeostasis.

The other parts of the brain have distinct functions that do not include the control of involuntary actions. For instance, the cerebellum is primarily involved in coordinating voluntary movements and balance, while the cerebrum is responsible for higher cognitive functions, sensory perception, and voluntary motor control. The thalamus acts as a relay station for sensory and motor signals but does not manage autonomic functions. Therefore, the brainstem's role in overseeing involuntary actions like breathing makes it the correct answer.