By Elizabeth A. Murray, Mount St. Joseph University
Among the most interesting muscles in the entire body are those that create our facial expressions. These are pretty unusual, since while they originate on bone, most muscles of facial expression insert on the skin.
Unique and Unusual
Rather than moving bones, the facial muscles literally steer the skin of the face around to result in a vast array of intricate patterns. These complex facial expressions are fairly unique to primates and are most well developed in humans.
While your dog can pull back the corners of his mouth and expose his teeth to snarl, he doesn’t have the nuances of facial expression around the eyes, the forehead, or the mouth that you have.
There are characteristic maps of human facial expressions, and many of them are universally recognized around the world. Looking at these, you immediately get a sense of whether the person is surprised, puzzled, angry, disgusted, sad, or happy.
And, as strange as it seems, these facial expressions are solely due to the movements of facial skin. Moving skin might seem odd, but maybe you’ve seen a horse, for example, shaking the skin of its back to deter flies; these movements of facial skin are similar, and are seen to varying degrees in different mammals.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Groups of Facial Muscles
There are several main groups of facial muscles to consider: Some muscles of facial expression are associated with the forehead and eyes, there’s a group around the mouth, and some odds and ends in between.
And, as a group, all muscles of facial expression are supplied by cranial nerve VII, the facial nerve. But the trigeminal nerve—cranial nerve V—provides sensations from the face. The name trigeminal implies its three main branches, and each one supplies sensations from a portion of the face.
Its ophthalmic branch supplies skin of the forehead and down the nose, mainly by the supraorbital nerve; the maxillary branch supplies skin of the cheeks by the infraorbital nerve, as well as being sensory to the upper teeth; and its mandibular branch supplies skin of the chin and lower face, mainly by the mental nerve, and is also sensory to the lower teeth.
If any of these branches become inflamed, a person can have excruciating pain from one or more regions of the face. So facial skin is covered by a different cranial nerve than our facial muscles.
Muscles around the Eyes
The frontalis muscle runs vertically within the skin above the eyes and wrinkles the forehead. The corrugator supercilii muscle draws the eyebrows together, wrinkling or corrugating them.
A circular muscle called the orbicularis oculi, an orb-shaped sphincter-like muscle, encircles each eye. It causes squinting when we use the peripheral fibers but causes blinking or closure of the eyelids when we use the portion within the eyelid.
Muscles around the Mouth
Around the mouth, we have another circular muscle called the orbicularis oris— from oral, meaning “mouth”. It is the muscle that puckers the lips. Along either side of the nose is a vertical muscle called the levator labii superioris—its name tells us that it elevates the upper lip, since labium means “lip”.
The risorius is a horizontal muscle that can pull the corners of the mouth posteriorly. These two—levator labii superioris and risorius—fuse with the edges of orbicularis oris, so not all of these muscles insert on the skin. Some actually attach to each other.
Smiling and Pouting Muscles
Two other muscles that relate to the orbicularis oris include the zygomaticus major, which is our smiling muscle. It originates from the zygomatic bone at the prominence of the cheek and passes inferomedially to fuse with orbicularis oris. Its counterpart is the depressor anguli oris, a name that means “to depress the angle of the mouth”—as in frowning. Inferior to the mouth is the mentalis—it’s a deeper muscle that protrudes the lower lip, as in pouting.
Another deep muscle associated with the oral region is called the buccinator. This muscle is interesting in that it is contained within the cheek wall. The buccinator is the muscle that we use to draw in our cheek wall, as in sucking through a straw, or to compress and expel air within your oral cavity, like when blowing a trumpet.
In addition, the buccinator is important to eating, since—along with the tongue—it helps continually reposition food for chewing, instead of having the food get stuck in the furrows between our cheeks and our gums.
Facial Muscles Not Related to the Face
There are a few remaining members of this group that are not really associated with the face at all. One is the occipitalis, which is like a horizontal band at the very back of the scalp. Surprisingly, it’s actually connected to the frontalis muscle of the forehead by a broad, flat tendon called an aponeurosis, and that tendon is one of the layers of the scalp. So despite its position, the occipitalis is part of the complex of subcutaneous muscles supplied by the facial nerve.
An additional muscle, the platysma, is within the skin of the neck. Sometimes it’s called the shaving muscle, because it can tighten the skin of the neck, as may be done while shaving. Like occipitalis, platysma is also supplied by the facial nerve.
Humans also have auricularis muscles deep to the skin around the ears. Cat, dog, and horse lovers may recognize how these muscles move and rotate the ears of those and many other mammals in the direction of sound. But in most people the auricularis muscles are vestigial remnants of our animal evolution.
Common Questions about Our Facial Muscles
The facial muscles are unusual since while they originate on bone, most muscles of facial expression insert on the skin. Rather than moving bones, the facial muscles literally steer the skin of the face around to result in a vast array of intricate patterns.
As a group, all muscles of facial expression are supplied by cranial nerve VII, the facial nerve. But the trigeminal nerve—cranial nerve V—provides sensations from the face. The name trigeminal implies its three main branches, and each one supplies sensations from a portion of the face.
Some of the facial muscles around the eyes are the frontalis muscle, the corrugator supercilii muscle, and the orbicularis oculi muscle.
