mysql trigger that updates only one specific record/row

Question

I have this table in mysql db:

ID	...	CREATE_DATE	UPDATE_DATE
Cell 1	Cell 2	Cell 4	Cell 6
Cell 3	Cell 4	Cell 7	Cell8

I need two triggers which have to behave like this:

1. when inserting a new row, create_date has to be instanced with current_timestamp
2. when updating a a row, the field update_date of this one has to be updated with current_timestamp

Could someone help me please?

I know trigger have "for each row " operations but I don't know how to act on a single row