Oracle Database Discussions

I've done some web research and I've learned that each Database Connection requires a certain amount of memory (2Mb + sort area + hash area). My question is: Is this memory dynamic or static? When the database comes up, does it set aside memory for X number of connections? Or does it only take the space when the connection is made, and then 'drop' it when the requirement no longer exists?

Forgive me if I've asked this question poorly - I am still quite new.

Thanks!