The muscles of the body originate in bone and insert into bone for body movements. Facial muscle usually originate in bone and occasionally in connective tissue and insert into bone for creating our innumerable facial expressions. Facial muscles are involved in other important bodily activities such as chewing food, and speaking.
In autopsy dissections, facial muscles appear to vary in size, shape, and the exact position of the origin and insertion. The origin and insertion positions are difficult to determine because facial muscles overlap each other and muscle fibers intertwine so much that distinguishing one muscle from another can be challenging.
There are even disputes about the identity of certain muscles as to whether certain muscles exists at all, or are part of another muscle. One such muscle in question is the risorius muscle located on both sides of the lips. Its job is to pull back the angle of the mouth for smiling and laughing. This muscle may be absent in some people or described as part of the neck muscle, the platysma.
In certain ways, you might compare how facial muscles work creating expressions to preparing a Chinese herbal formula. An herbal formula begins with a primary herb that is commonly responsible for the main action of the formula. With the addition of supplementary herbs, the effects of the primary herb such as taste and temperature can be modified. By maximizing and minimizing the amount of the additional herbs added to the formula, the overall effect of the primary herb will be significantly different from the primary herb working alone.
Like a primary herb, a primary muscle is commonly responsible for the expression of a feeling. With the addition of other muscles combined with the length and strength of each muscle contraction, the effects of the primary muscle can be modified. By maximizing or minimizing the use of additional muscles necessary to create a specific expression, the overall effect and facial expression will be significantly changed.
For example, the zygomaticus major muscle is the primary muscle involved in smiling. It raises the corner of the mouth and cheeks. Used alone, it produces a professional, polite smile which a stewardess would customarily display greeting people. An authentic and warm smile, however, requires the addition of the orbicularis oculi muscle that surrounds the eyes. This muscle narrows the eyes, lifts the cheeks and draws the skin inward causing “crow’s feet.” Crow’s feet are the undesirable wrinkles that develop outside the corner of the eyes. Only by contracting the zygomaticus major and orbicularis oculi together will you produce a genuine smile.
Another example begins again with the zygomaticus major muscle. Add the frontalis muscle which covers the forehead and raises the eyebrow. If only one side of the frontalis muscle contracts, it raises the eyebrow only on that side. The addition of the nasalis muscle flares the nostrils. The combination of these 3 muscle working together may express slyness or even lust.
Even when we’re sleeping, our facial muscles can be working hard. This is evident when patients fall asleep during a microcurrent facial session. The frontalis muscle may contract especially during a vivid dream thereby deepening lines and furrows on the forehead. This we cannot change. However, I always mention to my patients that for best results, we should engage in as little conversation as possible. Clients want the best results, and most will comply.
References
http:/pmc.ncbi.nlm.nih.glv/articles/PMC8986498/
Anatomy of Facial Expressions, Uldis, Zar1n, 3rd Edition, Janaury 1, 2017