Functional Facial Anatomy: A Primer
Sandy Tsao, MD
Where are the safe areas to inject? What can we do in certain areas that we cannot do in others? In order to answer these questions, we need to understand the basic facial anatomy.
Remember that it only takes one complication to understand how significant the facial anatomy can be. As the neuromodulators change and as we become more knowledgeable about treatments, we have a better perspective. When we’re talking about facial anatomy, we’re thinking about the muscles of facial expression that run from the skull to the skin. These muscles are innervated by the facial nerve and are sphincters and dilators of the eyes, nose and mouth. It is key to understand that the wrinkles that we’re seeing are actually perpendicular to the action of the muscle. This is very important for us when we’re thinking about where the lines are and how we would like to get rid of them.
The facial skeleton is composed of fourteen stationary bones and the mandible. These fourteen bones form the basic shape of the face and are responsible for providing attachments for muscles that make the jaw move and control facial expression.
The facial nerve divides into five terminal branches for muscles of facial expression:
- Temporal
- Zygomatic
- Buccal
- Marginal mandibular
- Cervical
If you’re ever cutting or injecting into any of these areas, it is critical to think about the insertions and the direction of these nerves.
The skin of the face is supplied by the trigeminal nerve (V), except for the small area over the angle of the mandible and the parotid gland that is supplied by the great auricular nerve (C2 and 3). The trigeminal nerve (V) divides into three major divisions—the ophthalmic (V), maxillary (V2), and mandibular (V3) nerves.
The arterial supply comes from the common carotid artery and it will innervate and branch thoroughly throughout the scalp and the facial structures and drain via the jugular nerve. Why is this significant? Every time we inject, there is always the potential for a hematoma, a bruise or an injury. Understanding where that vasculature is and where the drainage spots are is helpful to minimize side effects.
Muscles
The Temporoparietalis is key to us because of the temporal nerve. This muscle allows us to raise our ears, widen our eyes, and retract our temples. This can be an ideal place to add a filler; however, it is critical to understand that the temporal nerve is a little deeper. Across the face we have the Frontalis muscle that allows us to raise the eyebrows, widen the eyes, and furrow the forehead. We often take advantage of this to minimize and soften the horizontal lines across the face.
In direct opposition are the depressor muscles of the upper face, which include the Corrugator muscles. These muscles interdigitate with the frontalis; they actually displace the brow inferomedially creating the frown. The Corrugator muscles work in conjunction with the Depressor Supercilii that causes medial brow frowning. Last not but not least is the Procerus muscle—a very important muscle because it not only displaces the brow medially, but also creates the horizontal bands that many patients are interested in improving.
Clinical Pearl-When you are influencing one set of muscles, almost always there is another muscle that is acting against it.
The Transverse Nasalis muscle is a muscle is that interdigitates with the opposite muscle as well as the Procerus muscle. This is the muscle that allows for depression of the cartiginous part of the nose as well as drawing the ala toward the septum. This muscle is what we refer to as the “bunny lines.” We want to be very careful with injections here because too low of injections can infect the smile lines. This is one muscle into which we directly inject and try to keep on the higher edge of the muscular complex.
The Orbicularis Oculi is muscle that has two parts—palpebral and orbital. It has two components, each of which need to be thought about because influence of one portion may influence another part of the muscle. This muscle helps us to open and close our eyes, allowing us to form tears. When we’re addressing this muscle, we’re generally dealing with the orbital aspect of the muscle. When injected correctly, this can provide softening of the crow’s feet. If you inject the Orbicularis Oculi too deeply, you can infect the smile by influencing either the Zygomatic Major or Minor or even the Labii Inferioris Superior.
Clinical Pearl-It is pertinent to understand your endpoints because you will have migration of the neuromodulators over a three- to four-month period of time.
Levator Muscles of the Mouth
The Zygomaticus Major helps to raise the angle of the mouth superiorly and posteriorly and helps our mouths smile or laugh. The Zygomaticus Minor runs medially to the Zygomaticus Major and allows the upper lip to displace superiorly and deepens the nasolabial furrow allowing us to make an expression of contempt.
What about the rest of the mouth? The Depressor Labii Inferioris displaces the lower lip inferiorly and slightly laterally. The consequences of which will allow for displacement of the skin downward and lateral pull to the mouth and potentially an uneven smile if the Mentalis muscle is injected to superiorly. The Risorius muscle is one of our elevators and as a consequence it displaces the skin of the cheek posteriorly, it stretches the lower lip, and displaces the corners of the cheek downward and lateral and we see a nice grin.
The Levator Labii Superioris Alaeque Nasi is an important to muscle to know because it dilates the nose and actually raises the upper lip. The Levator Labii Superioris muscle is responsible for raising the upper lip. This is one of the muscles that we like to target when we’re trying to get less of a grin. When a neuromodulator is placed into these muscles, you can see less “gummy” show in the upper lip.
The Orbicularis Oris is also a very critical muscle. It is quite large and has a number of insertions into it. This muscle helps to bring the lips together and protrude forward. The Buccinator muscle merges with the upper and lower lip muscles and helps to compress cheeks against the teeth along with tensing and contracting the cheeks for a nice pucker. Injection into the vertical Rhytids will allow for some softening of the lines created by that muscular action.
The Depressor Anguli Oris helps as a depressor muscle. It depresses the angle of the mouth resulting in an expression of grief. This muscle is often times sought after as a muscle either to relax by a neuromodulator or to uplift by dermal filler. The Mentalis elevates and protrudes the lower lip allowing for an expression of doubt. This is a critical area to avoid surrounding muscles so that the smile itself is not influenced.
The Platysma muscle is a large muscle that helps to shape not only the lower face, but also heavily influences our neck musculature. It results in the depression of the lower jaw, displaces the lower lip inferiorly, and allows for an expression of horror or fright.
Conclusions
In conclusion, knowledge of the facial muscles is paramount in procedures affecting facial animation. We must understand the relationship of facial muscles and associated nerves and vessels as well as the relationship of muscles and planes throughout the face.
MauiDerm News Editor-Judy Seraphine
