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The facial muscles, also known as mimetic muscles, are a group of muscles just beneath the skin of the face that are controlled by the facial nerve. The primary function of the facial muscles is the formation of facial expressions in order to express feelings and emotions. The facial muscles also serve other functions, such as blinking and keeping food from falling out of the mouth. The muscles involved in the process of chewing food, however, belong to a separate muscle group known as the muscles of mastication.
There are many different facial muscles that are each responsible for different aspects of facial expression, such as furrowing eyebrows or flaring nostrils. Several of these serve particularly noticeable or apparent functions. The occipitofrontalis muscle, which has components in the front and back of the top of the skull, is responsible for the muscular actions of the scalp, such as raising the eyebrows or furrowing the forehead. The procerus, nasalis, and depressor septi nasi muscles all control the muscles of the nose and contribute to actions such as crinkling the nose or flaring the nostrils. The orbicularis oculi is the muscle responsible for drawing the eyelids down over the eyes, or blinking.
Another muscle associated with the eyes called the corrugator supercilii is located above the eyebrows and pushes the eyebrows downward and toward the center of the face. This muscular motion primarily produces the appearance of suffering and unhappiness. As such, this muscle is sometimes referred to as the "frowning" muscle.
There are many muscles that control movement around the mouth as well. The orbicularis oris muscle is responsible for many movements of the lips, such as puckering or closing the mouth. The risorius muscle is the muscle of the mouth that is responsible for tugging at the corners of the mouth to produce a smile. Sincere smiles involve the zygomaticus major and zygomaticus minor muscles around the lip and cause wrinkles on the outside of the eyes with the orbicularis oculi muscles.
This difference in the facial muscles used in sincere and false emotional expressions illustrates the connection between emotion and facial muscle control. A great deal of research in psychophysiology has indicated that most facial expressions of emotion involve the same facial muscles in all people and are not significantly culturally dependent. This is part of the reason that the Facial Action Coding System, a system of classifying the particular arrangement of relaxed and contracted facial muscles, is useful for determining emotion. There tends to be at least some subtle difference in the facial muscles used to express different emotions or to express insincere emotions.