When do Development Team members take ownership of a Sprint Backlog item?

According to the Scrum Guide1, the Sprint Backlog is the property of the Developers and no one else can tell them which items they should work on. The Developers can select any item from the Product Backlog that they forecast they can complete within a Sprint. The Developers are self-organizing and decide how to turn Product Backlog items into an Increment of value. Therefore, no one owns a Sprint Backlog item, but the entire Development Team is accountable for it.

References: Scrum Guide