In Prefixes^x, Negatives^x, Pronunciation^x

Are only these prefixes (a-, non-, in-, dis-, un-) negative one? What about anti-, contra-, counter-, de-, ex-, and extra-? Aren't they sometimes negative, too? Do negative prefixes have influence on pronunciation?

Hi micawber, Thanks for your information. Meanwhile, do you know the reasons for their present usages like dis- in disappointment,un- in unimportant,etc.Are there any rules for their usages or just they are employed inaccordance to better pronunciation. praveen.