Scrum, by its very nature, is deliberately non-prescriptive -- at it's heart, Scrum relies on simplicity and common sense. To that end, then, Scrum creates a very simple alignment of roles and responsibilities that, when adhered to, create significant motivation within the ranks of developers and management, clearly showing how each role contributes to the end goal of innovation and imagination born from empowerment and collaboration.
The Product Owner provides the vision and direction. He or she provides the "what?" in product development.
The Scrum Team provides the engine of product development. They provide the "how?" in product development.
The Scrum Master provides the coordination and consistency. He or she keeps the wheels of product development moving in the most effective manner possible.