The Muscles Of Expression

We have ways of making you laugh. Dr. Duchenne of Bologna, a nineteenth-century French scientist, became famous for his explorations of muscle function using electrical stimulation. In his book Mecanisme de la physionomie humaine, he illustrated the actions of many of the facial muscles by photographing subjects whose faces he "stimulated" with electrified needles (it's said to be a very unpleasant feeling). Here Duchenne demonstrates the action of the zygomatic major, touching the ends of the muscle— on the zygomatic arch—with his electrodes. The muscle reacts by contracting, pulling the mouth into a smile.

Zygomatic ArchFear Facial Expressions DrawingsMscle Fascial ExpressionMuscles Facial Expression Actions

Duchenne used his technique to attempt to demonstrate emotions as well as individual muscle actions. Here multiple electrodes are employed, applied to both the neck and the forehead, to illustrate the expression of fear. The muscles activated include the corrugator, the frontalis (forehead), and the risorius and platysma (neck).

Muscle Resorius

Several actors portraying "anger" from Charles Darwin's Expression of Emotions in Man and Animals. Darwin's book remains the best written on the subject. Much of his information came from his own meticulous observations of family and neighbors. But the book's illustrations—though full of period charm—are not its strong point. Even today, good photos of facial expression are not plentiful, and Darwin made what use he could of his limited sources; his best pictures are those from Duchenne.

How Facial Muscles Act

Face MusclesFacial Muscle Expression

In what they do, and how they do it, the facial muscles are different from other muscles in the body. Most of our muscles, like the biceps in the arm or the hamstrings in the leg, stretch from one bone to another, usually across a joint. When these muscles contract, the bones involved are brought closer together, often bending at a joint. Muscles always pull things together; it's the only way they work. They shorten, and their ends approach. They never push. For example, when the biceps contract, the radius in the forearm is pulled closer to the humerus in the upper arm, and the arm bends. When the hamstrings contract, the tibia approaches the femur, and the leg bends.

Facial muscles, however, usually have just one fixed end, attached directly or indirectly to the bone of the skull. The other end of the muscle is stitched into the skin (or into another muscle that attaches to the skin). When a muscle of expression contracts, skin, rather than bone, moves. The portion of skin near the end-strands of the muscles is pulled in the direction of its attachment on the bone.

Take the smiling muscle, the zygomatic major. Its bone-end attachment is on the cheekbone, just below the outer corner of the eye. Then the muscle stretches diagonally downward toward the mouth, where it attaches indirectly to its outer corner. When it contracts, the corner of the mouth rises up toward the cheekbone, and we smile. This is typical of the way most of the muscles of expression work.

Facial muscles do their work by pulling on the skin, unlike most other muscles, which are designed to move the bones. When a facial muscle contracts, it creates very visible changes; often a whole hill-and-valley landscape of bulges and wrinkles appears, as an area of the face folds on itself.

The zygomatic major is a typical muscle. It has a fixed end (A) attached to the zygomatic arch and a free end (B) attached to the corner of the mouth. A smile is the result of B approaching A. The nasolabial fold (C) is formed at right angles to the direction of pull; most wrinkles arise in a similar fashion. Note also the bulging cheeks (D) and wrinkles under eyes.

The Importance of Wrinkles

When the zygomatic major contracts, and its mouth end rises towards the cheekbone, the skin caught between the two ends of the muscle has nowhere to go. The skin in the cheeks, pressed up from below, bulges out like a tiny balloon being squeezed.

Above and below this bulge, wrinkles appear. The wrinkle that runs from the side of the nose to the side of the mouth is particularly noticeable. This crease, the nasolabial fold, is a perfect example of the sort of wrinkles that most frequently form when expression muscles contract: it lies at right angles to the direction of the pull. Similarly, the horizontal wrinkles that appear when we raise our eyebrows are perpendicular to the vertical pull of the forehead muscle. Look at the vertical folds that appear when you frown; the frowning muscle pulls directly across this fold.

Though overall patterns tend to be recognizably the same, details of wrinkle lines are quite different from person to person. The age of the individual is probably the most important factor in wrinkling. Very young people might not show any wrinkles at all when they lift their brows, while on older people, many permanent wrinkles may make new wrinkling difficult to perceive.

Thin people and obese people have different-looking smiles, as do men and women. A smiling woman would tend to show fewer crease lines than a smiling man of the same age (all other factors being equal) because of an extra layer of fatty tissue always present under a woman's skin.

The strength of the pull is also a factor. If we smile half-heartedly, some of the folds might appear only faintly, or not at all. But if we smile widely, added creases and dimples might form.

Signature Wrinkles

The wrinkles that arise when a particular facial muscle tightens are like its signature: distinctive and recognizable. We have discussed a few of these signature wrinkles, like the nasolabial fold for the smile. Wrinkles are one of the keys to understanding and depicting expression—they are part of

WRINKLES RELATED TO FACIAL EXPRESSION

Same expression, different age. Wrinkling when we smile is not a factor of age, but the nature and amount of the wrinkling is. The fundamental pattern of the smile is the same in both faces, but the older face shows a more complex version of the pattern, with more minor wrinkles. Almost all the wrinkles on the older face (bottom) are permanent; they merely deepen when she smiles.

Same expression, different age. Wrinkling when we smile is not a factor of age, but the nature and amount of the wrinkling is. The fundamental pattern of the smile is the same in both faces, but the older face shows a more complex version of the pattern, with more minor wrinkles. Almost all the wrinkles on the older face (bottom) are permanent; they merely deepen when she smiles.

Risorius DimplesMuscles Facial Expression

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Responses

  • dora goodbody
    How muscles are used in facial expressions?
    7 years ago
  • jennifer
    What muscle is difficult to palpate because it runs under the zygomatic arch?
    7 years ago
  • Ursula
    Which two facial muscles are employed when we are afraid?
    7 years ago
  • aatifa selam
    What is the insertion of facial muscles involved with facial expressions?
    6 years ago
  • noora johanson
    How to stretch muscle of facial expression?
    6 years ago
  • pia
    What muscles move the facial expressions?
    6 years ago
  • Orestilla
    How to eliminate smile wrinkles in the zygomatic arch?
    4 years ago
  • tyko
    Why do the muscles of facial expression move the skin rather than a joint?
    4 years ago
  • Tarquinia
    Which two facial muscle are employed whe e fear?
    3 years ago
  • AWATE
    How to draw dimple step by step?
    2 years ago
  • mantissa
    How to draw cheek dimples?
    2 years ago

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