Which of the following organs is part of the nervous system?

The spinal cord is an essential component of the nervous system, which serves as the primary pathway for transmitting nerve signals between the brain and the rest of the body. It is housed within the vertebral column and is critical for both reflex actions and the coordination of voluntary movements. The spinal cord is composed of neural tissue and is encased in protective structures, allowing for the efficient processing and communication of information throughout the body.

In contrast, the heart, while vital for the circulatory system, does not belong to the nervous system. Sweat glands and skin are part of the integumentary system, which plays a role in protection and thermoregulation but does not primarily function in sensing and transmitting signals like the nervous system. Thus, the spinal cord's significant role in nerve signal transmission and coordination of bodily functions establishes it as an integral organ of the nervous system.