What are the facial muscles?
The facial muscles are the muscles in the face that surround the eyes, nose, mouth and ears. Unlike other muscles of the body, they do not pull across joints from bone to bone, each with a tendon as an attachment point.
Instead, the facial muscles attach to the skin and soft tissues of the face. This allows the facial muscles to move the skin and soft tissues against the bony support of the skull. This causes furrows, wrinkles and dimples that change the expression of the face. The facial muscles are therefore also called mimic muscles because they have a strong influence on facial expressions and have a decisive effect on facial expressions.
All weight muscles are supplied by the facial nerve.
The facial muscles are divided into five groups:
The muscles of the cranial roof
The muscles of the cranial roof – collectively referred to as the epicranius muscle – pull from the front, back and sides to a tendon plate that is firmly attached to the scalp and can be easily moved against the periosteum.
The facial muscles surrounding the eye
Both eye sockets are surrounded by a ring muscle (Musculus orbicularis oculi): These facial muscles radiate into the tear duct, lacrimal sac, and eyelids, respectively. They make possible the blinking of the eyelids and the slight closing of the eyelids during sleep, as well as the firm squinting of the eyelids. In the latter, the skin around the eye is pulled toward the center, resulting in wrinkles at the outer edge of the eye, called crow’s feet.
The eyebrows pull these facial muscles inward and downward. They also dilate the lacrimal sac and provide for the movement of tear fluid.
Fibers of the orbicularis oculi muscle pull the eyebrows toward the center and downward – the facial expression triggered by the facial muscles thus becomes threatening, lurking.
The runt of the brow (Musculus corrugator supercilii), which depresses the skin above the center of the eyebrow, pushes the skin into vertical folds and frowns – the face gives the impression of concentration and reflection.
The descender of the brow (procerus muscle), which originates at the bridge of the nose, creates transverse wrinkles at the root of the nose and smooths the frown lines.
The facial muscles around the mouth
The depressor of the corner of the mouth (Musculus depressor anguli oris) pulls down the corner of the mouth and the upper lip respectively, flattening the upper area of the nasolabial fold.
The sinker or quadrilateral muscle of the lower lip (Musculus depressior labii inferioris) pulls the lower lip downward.
The smile muscle (musculus risorius) pulls the corner of the mouth to the side and upward, forming the dimples of the cheeks.
The lifter of the upper lip and nostril (Musculus levator labii superioris alaeque nasi) comes from the bridge of the nose and the inner corner of the eye and lifts the nostrils, the nasal lip furrow and thus the upper lip. It causes oblique folds that run from the inner corner of the eye to the center of the bridge of the nose.
The upper lip lifter (Musculus levator labii superioris) lifts the nasal lip furrow and thus also the upper lip.
The lifter of the corner of the mouth (Musculus levator anguli oris) raises the corner of the mouth.
The small and large zygomatic muscles (Musculus zygomaticus minor et major) run in the area of the right and left cheek, respectively. These facial muscles pull the nasal lip furrow and thus also the corners of the mouth to the side and upward. They are the actual laugh muscles among the facial muscles.
The chin muscle (musculus mentalis) pulls in the skin to the chin dimples, lifts the chin skin and pushes the lower lip up and forward – you draw a “pout”.
The facial muscles around the nasal opening
The depressor of the nasal septum (Musculus depressor septi) pulls the nasal septum downward.
The nasal muscle (Musculus nasalis) compresses the nasal opening and bends the cartilaginous part of the nose against the bony part.
The facial muscles in the area of the ears
These include facial muscles that move the auricle as a whole on the head:
The anterior ear muscle (Musculus auricularis anterior) pulls the pinna forward, the superior ear muscle (Musculus auricularis superior) pulls it upward, and the posterior ear muscle (Musculus orbicularis posterior) pulls it backward.
Muscles that originate and also attach to the auricle are developmental remnants of a sphincter of the external ear. In many animals, these muscles, which also belong to the facial muscles, deform the auricle; in humans, they are degenerated and meaningless.
What is the function of the facial muscles?
In the infant, one can observe how taste sensations influence facial expressions via the facial muscles. For sweet things like breast milk, for example, the baby sucks on the breast with its lips and tongue. When things taste bad, the mouth is opened, the upper lip is lifted and the lower lip is lowered so that the tongue does not come into contact with the taste. In children from eight months of age, the mouth acquires a square shape in this case, which is still adopted later in life when similar ideas of disgust develop in the psyche.
When unpleasant smells are detected, the eyelids are opened and closed and the nose is wrinkled. When unpleasant sounds are heard, the eyes are often closed as well. Defensive movements can even become threats in extreme cases, when in anger the upper lip is raised by the facial muscles to such an extent that “the teeth are shown”.
The facial muscles also determine the shape of furrows in the face that do not change – the nasolabial fold that pulls from the outer edge of the nose wing to the corner of the mouth, and the fold under the lower lip that pulls up on both sides to the corner of the mouth. With age, as the skin loses its tightness, these wrinkles become deeper.
Where are the facial muscles located?
What problems can the facial muscles cause?
In the case of paralysis of the facial muscles (facialis palsy), movements of the mimic muscles on the affected side are not possible – the face “hangs”.
When external sensory stimuli are absent, the corresponding purpose movements made possible by the facial muscles are also absent. In congenital blindness, for example, facial expressions in the forehead and eye area are absent.
A facial spasm (spasmus facialis) is a usually unilateral, involuntary and unsuppressible spasm of the facial muscles. It may affect individual or all muscles of the mimic musculature supplied by the facial nerve.
Diseases that affect the motor function of the facial muscles (and other muscles) lead to mimic rigidity, a “mask face” (amimia). This is the case, for example, with Parkinson’s disease.
A leading symptom of tetanus (lockjaw) is spasms of the facial muscles that lead, among other things, to a kind of permanent smile (risus sardonicus).
Tic disorders are repeated, purposeless arbitrary movements of facial muscles, such as a blink spasm or lip biting, that make normal movements difficult.
