Synergists of facial muscles

This article is also available in a video format in our Bell's Palsy Video Course. Click here to learn more. Human face is the most sophisticated and context-rich communication tool that ever existed. It was perfected for its purpose by millions years of evolution.

Although a number of muscles may be involved in an action, the principal muscle involved is called the prime mover , or agonist. Because it can be assisted by the brachialis, the brachialis is called a synergist in this action Figure A muscle with the opposite action of the prime mover is called an antagonist. Antagonists play two important roles in muscle function: 1 they maintain body or limb position, such as holding the arm out or standing erect; and 2 they control rapid movement, as in shadow boxing without landing a punch or the ability to check the motion of a limb.

Surface EMGs were recorded simultaneously from ipsilateral pairs of facial muscles while subjects made three different common facial expressions: the smile, a sad expression and an expression of horror, and three contrived facial expressions. Central peaks were found in the cross-correlograms of EMG activity recorded from the orbicularis oculi and zygomaticus major during smiling, the corrugator and depressor anguli oris during the sad look and the frontalis and mentalis during the horror look. The size of the central peak was significantly greater between the orbicularis oculi and zygomaticus major during smiling. It is concluded that co-contraction of facial muscles during some facial expressions are accompanied by the presence of common synaptic drive to the motoneurones supplying the muscles involved. Central peaks were found in the cross-correlograms of EMG activity recorded from the frontalis and depressor anguli oris during a contrived expression.

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