Fibromyalgia syndrome primarily involves which of the following systems?

Fibromyalgia syndrome primarily involves the nervous and muscular systems, as it is characterized by widespread musculoskeletal pain, along with fatigue, sleep, memory, and mood issues. The central nervous system plays a crucial role in how pain is perceived and processed, which is central to fibromyalgia's symptoms. Additionally, the muscular system is significantly affected, as the condition leads to muscle pain and tenderness.

While the muscular system is indeed involved in fibromyalgia, the digestive system is not one of the core systems directly impacted by the disorder in terms of its primary symptoms. Other systems like the urinary and reproductive systems may not have a meaningful relationship to fibromyalgia, making them less relevant in this context. Therefore, the most accurate understanding of fibromyalgia's primary involvement points to the nervous and muscular systems, clarifying why the other options do not provide a comprehensive view of the syndrome's effects.