I believe you are actually referring to the product AppMon - the term IO isn't used in Dynatrace as far as I know.
This document has descriptions for all of those fields. Note that for IO this is a calculated value based on any time that cannot be attributed to sync time, cpu time, or suspension time. Different activity within the PurePath is attributed to the other categories.
Response time for a server side PurePath is based on when the entry point method (the first one in the tree) has finished it's execution. There is another time for PurePaths called "duration" which is when all activity within the PurePath has completed (even after the entry point method has completed) and this is commonly larger than response time in PurePaths with lots of asynchronous activity occurring.