Does my node server need to manually end the response before the function ends?

Does my node server need to manually end the response before the function
ends?

I have a node server and I'm using express to process POST requests to it.
My question is, do I have to call response.end() before my processing
function ends or will that happen automatically?
Why I'm asking is because my server works as expected for the first few
requests, then it starts throwing "request timeout" errors, so I'm trying
to track down the issue.
I should also note that I always send something in the response using
response.send() if that makes any difference.