Are Usenet newsgroups managed centrally?

[radiofan]

So - it's very possible that I'm just not understanding the inner workings of Usenet and that this question has a really obvious answer, but I can't figure this one out, so I thought I'd ask here in the hope that someone could explain. Let's say that a new newsgroup gets created called "alt.test.newsgroup":

1. How are Usenet providers notified that this newsgroup has been created - must they be subscribed to a Usenet server that in turn gets notified of its creation - or am I just misunderstanding the concept of this entirely?

2. When a new post is made to a Usenet newsgroup (let's say that it was made by a subscriber of "usenet-provider.com"), how do other Usenet providers receive the content - does the entire Usenet system rely on a central server (or similar) to distribute the post?

Thanks.