MUSCLES OF THE FACE: CHARACTERISTICS AND FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2025

The muscles of the face are so many and so varied that it can be very difficult to imagine how such a large number of muscle groups can be distributed in such a small space, which also have such specific and differentiated functions.

The complexity of facial expression, in addition to the functions of phonation and swallowing, require not only many muscle groups, but also extraordinary coordination between the different muscle groups to achieve such a wide variety of movements, ranging from a simple wink until the power to whistle.

In general, the muscles of the face can be divided into two large groups: those of small size and with a function limited to facial expression, and those of large size with a fundamental role in functions as important as speech, eating and even the breathing.

A detailed analysis, muscle by muscle, of the more than 15 muscular structures found in the face is far beyond the scope of this post, to the point that it takes years of anatomy study and surgical practices to know them in detail. On this occasion, all of them will be mentioned and only the most relevant will be described.

General characteristics

The vast majority are flat, thin muscles with a fairly discreet size / strength ratio; that is, they are not muscles that have many muscle fibers or that generate great power.

Almost all take two insertions at different points, one in the bones of the face and the other in the skin of the face or the aponeurosis of a neighboring muscle; sometimes it can be both.

Larger muscles are the exception to this rule. These are the masseters, which have their two insertions on bone surfaces; They are capable of moving a joint and, per square centimeter of surface area, are among the most powerful muscles in the body.

Classification and functions

The muscles of the face can be classified according to their function and according to the anatomical area with which they are related.

Depending on their function, the muscles of the face can be divided into muscles of expression and muscles of chewing.

The muscles of expression almost invariably take insertion in bone and skin, while those of chewing always do so in bony surfaces.

On the other hand, according to their anatomical location, the muscles of the face can be divided into:

- Muscles of the ears.

- Muscles of the eyelids and eyebrows.

- Muscles of the nose.

- Muscles of the mouth and lips.

Muscles of the pinna

Due to the location of the pinna, its structure and the particular evolution of the human being - which no longer depends so much on the ear to survive - the muscles of the pinna are considered muscular vestiges.

Although they are present, their function is null. In fact, the cases of individuals with the ability to move their pinna are exceptional.

In those cases in which it is possible to move them, it is due to the action of the anterior, posterior and superior auricular muscles, present in all people but in very few cases with enough force to have a visible effect.

Muscles of the eyelids and eyebrows

Its main function is to generate movement of the eyebrows, frown and, above all, allow the eye to open; to this group belong:

- Occipito-frontal muscle

- Pyramidal muscle

- Superciliary muscle.

- Orbicularis muscle of the eyelids.

The latter is the most important of all, since it allows ocular closure; it is a large, flat, circular muscle that surrounds the outer part of the orbits. It is divided into several portions that allow you to gently close your eyes or "squeeze" the eyes while closing.

The opposite function (eye opening) is due to the synergistic action of the levator muscle, which "lifts" the eyelid like a blind as the orbicularis oculi relaxes, allowing the lower eyelid to drop almost by gravity.

It is important to remember that the levator upper eyelid is not considered a muscle of the face, since it begins inside the orbit and ends in the upper eyelid; Furthermore, its innervation depends on the 3rd cranial nerve (common ocular motor), unlike the muscles of the face, whose innervation is the responsibility of the 7th cranial nerve (facial nerve).

Muscles of the nose

Of these muscles, only one (pyramidal of the nose) has to do with expression, while the rest have a specific function in the respiratory system.

- Pyramidal nose

- Transverse of the nose.

- Mirtiform.

- Nose dilator.

The mirtiform muscle is responsible for "depressing" the nasal ala and thus closing the entrance to the nasal passages, this being particularly useful in limiting the entry of impurities such as dust into the upper respiratory tract.

For its part, the transverse and dilator of the nose act synergistically to do the opposite: dilate the entrance of the nostril to allow air to enter more easily.

In general, its action is not visible except in cases of severe respiratory distress, when its effect is so evident that it gives rise to a clinical sign known as nasal flaring, which consists of the elevation of the wing of the nose with each inspiration..

Muscles of the mouth and lips

They are the most numerous and most widely distributed, occupying more than 60% of the total area of ​​the face.

These muscles are responsible for most of the facial expressions. In addition, some help in phonation, and some very particular allow chewing: the masseters

- Buccinator.

- Orbicular of the lips.

- Common elevator of the nose and upper lip.

- Own lift of the upper lip.

- Canine muscle.

- Major zygomatic.

- Minor zygomatic.

- Risorio.

- Triangular of the lips.

- Square of the chin.

- Chin tassel.

- Masseter.

All of these muscles, innervated almost entirely by the facial nerve, are responsible for the hundreds of facial expressions on the human face.

For example, the smile is a consequence of the contraction of the risorio and the zygomaticus major and minor muscles; Likewise, the slight contraction of this pair of muscles allows to elevate the lip commissure.

For its part, the buccinator retracts the corners of the lips; This allows whistling, playing wind instruments, and dislodging food that accumulates in the vestibular area of ​​the gums.

The orbicularis oculi is another specialized muscle that allows the mouth to be closed, in addition to helping in the complex of movements necessary to suck.

Finally there is the masseter which, together with the pterygoid muscles (belonging to the pterygoid fossa), is part of the chewing muscles.

It is capable of exerting a pressure of 90 kg / cm2, which makes it one of the strongest muscles in the body considering the size / force ratio exerted.

It takes insertion in the zygomatic arch and in the ascending branch of the lower jaw, allowing mouth closure and chewing. For this they work in synergy with the rest of the chewing muscles and in coordination with the neck muscles, responsible for the mouth opening (digastric, mylohyoid, infrahyoid muscles, among others).

References

1. Pessa, JE, Zadoo, VP, Adrian, JE, Yuan, CH, Aydelotte, J., & Garza, JR (1998). Variability of the midfacial muscles: analysis of 50 hemifacial cadaver dissections. Plastic and reconstructive surgery, 102 (6), 1888-1893.
2. Gasser, RF (1967). The development of the facial muscles in man. Developmental Dynamics, 120 (2), 357-375.
3. Goodmurphy, CW, & Ovalle, WK (1999). Morphological study of two human facial muscles: orbicularis oculi and corrugator supercilii. Clinical Anatomy, 12 (1), 1-11.
4. Szentagothai, J. (1948). The representation of facial and scalp muscles in the facial nucleus. Journal of Comparative Neurology, 88 (2), 207-220.
5. Freilinger, G., Gruber, H., Happak, W., & Pechmann, U. (1987). Surgical anatomy of the mimic muscle system and the facial nerve: importance for reconstructive and aesthetic surgery. Plastic and reconstructive surgery, 80 (5), 686-690.
6. Rubin, LR, Mishriki, Y., & Lee, G. (1989). Anatomy of the nasolabial fold: the keystone of the smiling mechanism. Plastic and reconstructive surgery, 83 (1), 1-10.
7. Schwarting, S., Schröder, M., Stennert, E., & Goebel, HH (1984). Morphology of denervated human facial muscles. Orl, 46 (5), 248-256.