how are pthreads on linux seen by scheduler

I've a question regarding pthread implementation on Linux.

Suppose a process has 5 threads. Now how does the scheduler sees these threads (or doesnt see at all). e.g. When scheduler is invoked, does it only schedule the main process, and then its the onus of the main process to schedule between each of its thread.

Or is it the other way, that scheduler schedules each thread as if it is a separate process.