The risorius is a facial muscle which pulls the corners of the lips out and back (towards the ear).
The synergist to the smiling muscle (zygomaticus major) is the orbicularis oculi muscle, which is responsible for the contraction around the eyes and contributes to the overall expression of a smile.
It is primarily the zygomaticus major and risorius muscles that are responsible for a smile, aided in part by the action of the buccinator :)
The position of the frontalis is over the frontal bone or the forehead. This muscle works with the occipitalis which is over the occipital bone in the back of the head. It's action is to elevate the eyebrows.
There are approximately 642 skeletal muscles within the typical human, and almost refers to the action of each muscle from the standard anatomical position.
Static Stability
mentralis buccula
antagonist muscle
THe action of the digastric muscle is to depress the mandible or evaluate the larynx
The frowning action.
gdg
It represents contracting or shortening of a muscle.
Which muscles? If all the muscle are clenched it will be perfectly still but that could be in any position depending on what position the arm was in ot start with.