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Overview of the muscles responsible for facial expression.
So, it’s believed that only seven percent of our communication is verbal while thirty eight percent is thought to be tone of voice and the remaining fifty five percent is considered to be nonverbal. Nonverbal communication involves body language, gestures and, of course, facial expressions. Facial expressions form a huge part of our nonverbal communication. I mean unless you have a stellar poker face, the chances are that most of the time your thoughts and feelings are plastered across your face before you say anything at all. While body language and gestures can vary significantly between cultures, the facial expressions for happiness, sadness, anger, and fear are similar throughout the world.
So, today, we’re going to talk about the muscles that allow you to show you these emotions – the muscles of facial expression. Before we begin, let me give you a quick overview about what we’re going to cover in today’s tutorial. Let’s start with a little introduction to the facial muscles as a whole, talking about their gross anatomy and function, their innervation, their blood supply, and their lymphatic drainage. We’ll then look at each muscle individually exploring them within their groups. These groups include the orbital group, the nasal group, the oral group, the auricular group, and the ones we find in the scalp and neck regions. Finally, we’ll conclude our tutorial with some clinical notes on facial nerve paralysis.
Okay, time to introduce you to the muscles of facial expression.
So, here we can see our lovely gentleman volunteer that seems to feature heavily in our Kenhub tutorials. If we dissect away his skin, connective tissue and vasculature – a bit gruesome, I know – we can his facial muscles nice and clearly. The muscles of facial expression, also known as the mimetic muscles, are flat skeletal muscles that lie superficially within the subcutaneous tissue or, in other words, under the skin.
Due to their atypical shape or morphology, it can sometimes be difficult to define the facial muscles using the classic system of origin and insertion, however, in general, they tend to arise directly from the bony landmarks of the facial bones or even adjacent muscles, and then go on to insert into either another facial muscle or into fascial connective tissue beneath the skin. As for function, these muscles contract and relax to control the expressions of your face, revealing whether you are happy, sad, angry, or frightened. This is why they are collectively called the muscles of facial expression.
In order for your facial muscles to work their magic, they need some innervation. They’re innervated by branches of the seventh cranial nerve, also known as the facial nerve. Before we move on, I’ll also show you this nerve from a lateral view. The blood supply to the muscles of facial expression is largely derived from branches of the external carotid artery. The facial artery is a branch of the external carotid and supplies most of the facial muscles. Venous return from the facial muscles is mainly via tributaries of the internal jugular vein. The facial vein is a tributary of the internal jugular vein and drains most of the muscles of facial expression. As you can see from this image, it follows a similar path to that of the facial artery.
As for lymphatics, most lymph from the face drains into three groups of lymph nodes. The first group are the submental nodes, and as the name suggests, these nodes are found beneath the chin. They drain lymph from the lower lip and, of course, the chin. Next, we have the submandibular nodes which are found below the body of the mandible. These nodes drain lymph from the orbit, nose, cheek and the upper and lower lips. Finally, we can see the preauricular and parotid nodes which lie in front of the ear. These nodes drain lymph from the eyelids, nose, and cheek.
Okay, now that I’ve introduced you to the muscles of facial expression as a whole, let’s move on to look at each muscle individually, exploring them within their groups. When we talk about these muscles, we’ll focus specifically on their functions and we’re going to start with the orbital group.
The orbital group consists of two muscles. The first one we’re going to talk about is the orbicularis oculi. As you can see, this is a large circular muscle that surround your eyes. The orbicularis oculi consists of three parts – an orbital part, a palpebral part, and a lacrimal part. Let’s go on to look at these parts in more detail.
The orbital part of orbicularis oculi consists of the outer rings you can see here highlighted in green. When this part of the muscle contracts, it closes the eyes forcefully and produces some wrinkling of the forehead. An example of when you use this muscle is when you wink, and I bet you wink just now to test it. If you didn’t, you should.
Next, we can see the palpebral part of orbicularis oculi. This part is found within the region of the eyelids and closes the eyes more gently such as when we blink. Lastly, we have the lacrimal part of orbicularis oculi. The lacrimal part is located medially and when it contracts, it compresses the lacrimal sac which aids in the flow of tears.
If we remove the orbicularis oculi, we can see the other muscle of the orbital group which is the corrugator supercilii. Even without skin, this muscle makes our skull here look somewhat annoyed and that relates to its function. This muscle lies deep to the eyebrows and when it contracts, it pulls the eyebrows medially and inferiorly. Unsurprisingly, it’s one of the muscles that’s active when frowning.
That’s us finished with the orbital group, so let’s move on to talk about the muscles of the nasal group. Again, the nasal group consists of only a few muscles, and the first one we’ll talk about is the nasalis muscle. This muscle is composed of two parts – the transverse part and the alar part. So let’s go on to look at these parts in more detail.
The transverse part of nasalis is this portion here highlighted in green, and as you can see, it forms the bulk of this muscle. When this part contracts, it compresses or narrows the nostrils whereas the alar part of nasalis flares or widens the nostrils.
Next, we have the procerus muscle. When this muscle contracts, it pulls the eyebrows downwards causing wrinkles in the skin on the bridge of your nose. You activate this muscle when you smell something unpleasant.
The last muscle of the group is the depressor septi nasi muscle. This muscle assists the alar part of nasalis with the flaring of the nostrils.
Now, it’s time of our largest group of facial muscles – the oral group. The first muscle of this group we’ll take a look at is the orbicularis oris. You may have noticed that like the orbicularis oculi, this is a large circular muscle, but instead of encircling the eyes, it surrounds the mouth. When this muscle contracts, it closes the mouth. It also purses and protrudes the lips. We used this muscle when we whistle or blow bubbles.
The next muscle we’re going to talk about is the buccinator muscle. As you can see, this muscle is located on both sides of the face and it forms the muscular base of the cheeks. The buccinator muscle has several functions. When it contracts, the cheek presses against the teeth and this prevents the buildup of food between the cheeks and the teeth. This muscle also aids in the forceful expulsion of air from the cheeks.
Located on either side of the nose, we can see our next muscle. The name of this muscle is a bit of a mouthful. It’s called the levator labii superioris alaeque nasi. This muscle assists the alar part of nasalis and the depressor septi nasi with the flaring of the nostrils. If we remove some of the more superficial facial muscles, we can see this muscle highlighted in green which is the levator labii superioris. As the name suggests, contraction of this muscle elevates the upper lip.
Moving laterally, we can see this muscle here, which is the zygomaticus minor muscle. When this muscle contracts, it pulls the corners of the mouth upwards and outwards. As such, it’s one of your smiling muscles. If you have a zygomaticus minor, then you must have a zygomaticus major which you can now see highlighted in green. Like its smaller buddy, it draws the corners of the mouth upwards and outwards, helping you pull that cheesy grin.
Deep to the zygomaticus muscles, we have the levator anguli oris. Contraction of this muscle lifts the corners of the mouth and, again, it’s best seen in action when you smile. The next muscle we’re going to talk about is the risorius muscle. The risorius muscle gets its name from the Latin word “risus” which means laughter and, sure enough, the risorius exists to help you express happiness. When it contracts, it draws the corners of the mouth upwards and outwards.
Let’s move on to some muscles found below the mouth starting with the depressor anguli oris muscle. This muscle antagonizes the levator anguli oris and when it contracts, it pulls the corners of the mouth downwards. This is best seen when you make a sad face. If we remove the depressor anguli oris, we can see the depressor labii inferioris. Contraction of this muscle pulls the lower lip downwards and outwards. Located in the region of the chin, we can see a muscle highlighted in green which is the mentalis muscle. When this muscle contracts, it lifts and protrudes the lower lip, which wrinkles the skin of the chin. When you use this muscle, you have what we in Scotland call a “petted lip”.
Okay, let’s move on to talk about the muscles that you use to wiggle your ears – the auricular group. The auricular group is made up of three muscles, and the first one we’ll talk about is the auricularis anterior which we can see here from a lateral perspective. This muscle is located anterior to the ear and when it contracts, it pulls the ear upwards and forwards.
Next, we have the auricularis superior muscle which as you can see is located superior to the ear. Contraction of this muscle lifts the ear. Located behind the ear, we have the last muscle of this group which is called the auricularis posterior muscle. When this muscle contracts, it pulls the ear upwards and backwards.
Time to move on to our last group of muscles of facial expression, the muscle of the scalp and neck. The first muscle we’re going to talk about is associated with the scalp that is called the occipitofrontalis. This muscle consists of two bellies - a frontal belly, also known as frontalis, and an occipital belly, also known as occipitalis. Note that we can’t see the occipital belly here as it’s located posteriorly, however, if we change to a lateral view, you can see where this muscle is found. These bellies are connected via the epicranial aponeurosis and as for function, the frontal belly elevates the eyebrows and wrinkles the forehead as you do when you’re surprised, whereas the occipital belly pulls the scalp backwards.
Finally, we’re on our last muscle of the tutorial which is found in the neck and is called platysma. This muscle lies in the superficial fascia of the neck and when it contracts, it tenses the skin of the neck. It also depresses the lower lip and draws the corners of the mouth downwards.
Now that we’re familiar with the muscles of facial expression, let’s move on to our clinical notes. Towards the beginning of our tutorial, I mentioned that the muscles of facial expression require innervation via the facial nerve to perform their functions. Therefore, in facial nerve paralysis, the ability of the facial muscles to move is impaired. Facial nerve paralysis has many causes including inflammation, stroke, petrous bone fracture, and brain tumors.
The most common cause of facial nerve paralysis is Bell’s palsy. This condition is thought to be caused by viral infections specifically the herpes simplex virus. Bell’s palsy causes inflammation of the facial nerve resulting in drooping of the muscles in the affected side of the face. Treatment include steroids, eye drops, and surgical tape to keep the affected eye closed while sleeping. This condition eventually resolves itself but can last up to nine months.
Before we bring our tutorial to a close, let’s quickly summarize what we’ve learned today. We started with an introduction to the facial muscles as a whole talking about their gross anatomy and function, their innervation, their blood supply and their lymphatic drainage. We then looked at each muscle individually, exploring them within their groups. These groups included the orbital group, the nasal group, the oral group, the auricular group, and the ones we’ve found on the scalp and neck. Finally, we talked about facial nerve paralysis in our clinical notes.
So that brings us to the end of our tutorial on the muscles of facial expression. I hope you enjoyed it. Thanks for watching and see you next time.