Many loans you have the option to pay down principal (thus still needing to make the monthly payments) or making prepayments (so you could suspend payment for a few months).
When you send in the payment you can write an explanation what to apply it towards.
If you just send extra money with no explanation, they usually have a default they will do - some companies apply it to principal, as matchewed said, some do to early payments, like StarryC said.
Call the company to see which, if either, option you have.
Also, to answer the question in the OP "What about an emergency?" you have to answer this: what is an emergency?