Which part of the CNS is the best protected and controls cardiac and respiratory functions?

The brain stem is the best protected component of the central nervous system (CNS) that also plays a crucial role in controlling vital autonomic functions such as cardiac and respiratory functions. This structure is located at the base of the brain, connecting it to the spinal cord and is encased within the skull and vertebral column, providing it with strong physical protection.

The brain stem is responsible for regulating basic life support functions, including heart rate and breathing rhythm, through various nuclei and centers, such as the medulla oblongata and pons. It acts as a critical point of control for involuntary actions essential for survival. When the brain stem is functioning properly, it ensures that the body responds appropriately to the demands of the environment, such as increasing heart rate during physical exertion or decreasing it during rest.

In contrast, the cerebellum primarily focuses on coordination and balance rather than vital functions, while the spinal cord serves as a conduit for signals between the brain and body, and the cerebral cortex is involved mainly in higher-level functions like reasoning, sensory perception, and voluntary muscle movements. Hence, while all these parts of the CNS are important, the brain stem's specific role in controlling autonomic functions makes it the most appropriate answer.