Which of the following is part of the nervous system?

The spinal cord is indeed a crucial component of the nervous system. It serves as the primary pathway for transmitting information between the brain and the body. The spinal cord contains nerve cells and pathways that facilitate reflex actions and the coordination of activities controlled by the nervous system. It plays a vital role in processing sensory information and coordinating motor control, thus contributing significantly to bodily functions and responses.

The other choices represent different systems or structures that do not belong to the nervous system. The pancreas is part of the endocrine and digestive systems and is responsible for producing hormones like insulin and digestive enzymes. Muscles, while essential to bodily movement, are part of the muscular system and are not classified as part of the nervous system. The cranium, while it protects the brain and is associated with the skeletal system, is not an active component of the nervous system itself.