Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged.
For a Class 1 lever the pivot lies between the effort and the load. A see saw in a playground is an example of a Class 1 lever where the effort balances the load.
The place where your skull meets the top of your spine is a Class 1 lever. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward.