Not a single muscle of his face--which in those days was still thin--moved.
Every muscle in her body was sore.
He was one large muscle with a direct gaze that made her overly self-conscious.
A deeper ache, as if she had the flu and every muscle in her body was on fire, was made worse by sleeping on the cold floor.
The iris contains a sphincter and a dilator muscle; the former, supplied by branches from the oculomotorius nerve, is under control of the will, whilst the dilator fibres belong to the sympathetic system.