Here's why:

* Nervous system: The brain is the control center of the nervous system. Scientists studying the brain are researching a vital component of this system.

* Scientific system: The scientist is part of a larger system of research, discovery, and knowledge creation. They use the scientific method, collaborate with other scientists, and contribute to the advancement of scientific understanding.

While the scientist isn't physically part of the nervous system, their research is focused on understanding and studying it.