The purpose of a 510k submission is to provide the FDA with documented evidence which proves that your device is equivalent to a preceding device that has already been approved for marketing. The FDA processes 510k submissions in 30-90 days and if your application is accepted, your submission will be posted to the FDA 510(k) database.
A Premarket Approval (PMA) is more in-depth than a 510k - it is used to prove that a new device is safe and effective for the end user and typically requires clinical trials with human participants along with laboratory testing. Under Section 515 of the act, all devices placed into Class III are subject to premarket approval requirements. The standards here are much higher than for 510k submissions, and the FDA has just 180 days to accept or reject the application.
References : Greenlight Guru, Cowper Law, Ken Block Consulting, USFDA