Happiness. Sadness. Fear. Anger. Disgust. Surprise. Those are universal emotions, and it takes five facial muscles to display each of them to the world. All humans have these muscles, but possession of other facial muscles seems to vary a great deal among individuals. Although 43 muscles have been identified in the face, it's not uncommon to have fewer. The complex process of identifying facial muscles and why their appearance is inconsistent is the real story here.
Counting facial muscles is not as easy as you'd think. In most body parts, muscles tend to be bulky, distinct and connected to bone. Facial muscles are flat, can be intertwined and may be fastened solely to skin. Thorough studies of facial muscles are done using cadavers, removing the skin to allow examination of the remaining tissue. It can be very difficult to measure muscle, because it, well, moves so easily, contracting or expanding when manipulated.
Once muscles have been individually identified, what is found? The universal muscles are around the eyes, across the forehead, along the cheeks, under the mouth and above the mouth leading down to the chin. These make it possible to relay messages anywhere in the world. No matter the culture, language, social class, politics or economics of a region, a smile signifies pleasure as clearly as a frown indicates unhappiness. Some of these muscles are also involved in eating, drinking and vision, so their use extends beyond exhibiting emotions. All five muscles seem to be present in all humans and are usually quite symmetrical.
Variations, however, have been found among "nonbasic" muscles (those not used for universal expressions). They are often intertwined, both physically and functionally, with other muscles. During fetal development they develop and differentiate slower than the universal muscles. Nonbasic muscles might be absent altogether in a person or, in the case of paired muscles, they might be markedly asymmetrical. Some of the common missing muscles include the risorius (retracts the sides of the mouth), the depressor septi (constricts the nostrils) and the nasalis (moves nasal cartilage).
The universality of some muscles, coupled with deviations of others, suggests an evolutionary aspect to facial musculature. Human development over time has ensured that important expressions can be understood despite geographical or societal differences. This still allows for individual and cultural variations.
While we have lots of facial muscles, some people want to suppress them to keep wrinkles at bay. A perfect job for Botox! (Don Murray/Getty Images)
The seventh cranial nerve, also called the facial nerve, controls our facial muscles. The nerve starts in the cerebral cortex and comes through your skull, stopping in front of your ears. It then branches off into five sections that affect your ability to move your facial muscles to make different expressions. Here are the nerve's branches:
These nerves control 43 facial muscles, though some people have fewer facial muscles than others -- up to 40 percent fewer. This variation in the number of facial muscles in humans is a fairly new discovery. A 2008 study by scientists at the U.K.'s University of Portsmouth examined the facial muscles of cadavers and found that the gift of facial muscles has not been parceled out equally among all of mankind. In fact, the face is the only part of the body that has such muscle variation from person to person [source: Science Daily].
Facial muscles are the best tools we have to give visual clues that reveal our emotions, from happiness to sadness and everything in between. And the muscles aren't just for facial expression either. For example, they're also integral to speech: The muscles that control the lips help us form voices the rest of the world can understand [source: Voice & Speech Source].
And what about everyone's favorite expression, the smile? There's a lot going on behind our skin to make one happen, and it's impossible to know the exact number of facial muscles involved in a smile, so we'll analyze one that only lifts the corners of the mouth -- a minimal smile, for someone you don't like very much. To get that tight smile, two pairs of muscles lift the upper lip, while three other muscle pairs raise the corners of the mouth -- 10 muscles in all, just to give a strained smile!
Meanwhile, a mildly serious frown takes three muscle pairs: one to drop the lower lip and one to drop the corners of the mouth, for a total of six muscles. So it only took six muscles to produce a small frown; and in this case, frowning took less effort than smiling. But every person and expression is different, so perhaps it's better to just turn that frown upside-down and not worry about it.
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