How to call a function in the code behind from jQuery?

Hi,
I need to do this: in an .aspx page, based on a radio button selection (I cannot use asp: radiobuttonlist here, needs to be plain html, due to new UI), then call an existing function in the code behind.
Basically the .aspx page used to use <asp:RadioButtonList> for this, and it uses a "OnSelectedIndexChanged="rblPaymentType_SelectedIndexChanged"" to display different views based on the user selection.
Now, we have a new UI, which does not work with the <asp:RadioButtonList>. So I need to use plain html <input type="radio"...> to replace the existing <asp:RadioButtonList>; thus I need to call the function in the code behind function from a Jquery, based on the user selection of this radio button.
Please let me know how I can do that? will it use an ajax call to a backend function? if so, how to do it?
If someone can provide some sample code to show me the idea, I'd appreciate it very ...