The muscles of facial expression are innervated by the seventh cranial nerve - the facial nerve.
The muscles of the face can be broken into three groups:
1) Orbital Group
2) Nasal Group
3) Oral Group
In addition to muscles in these groups, you have the occipitofrontalis muscle and the auricular muscles of the ear.
Four key muscles to remember are the:
2) Orbicularis oculi
3) Orbicularis oris
Remembering the names!
Think logically, and think of the meaning of the words, as they give an indication of the location and the function of the muscles. This is particularly important with the muscles in the oral group, for which there are numerous muscles with lengthy names.
depressor/levator - if the muscle is above the lip, it will elevate the lip, and so will contain the word levator, and vice versa.
labii - means lip!
superioris/inferioris - refers to the upper/lower lips
anguli - means "corner/angle"
So with this knowledge in mind, if someone comes up to you and asks "where can I find the depressor labii inferioris", don't panic and think you don't know what the hell it is, or where to find it - the clues are in the name. This muscle translates as "depressor of the lower lip", so you can thereby infer that the muscle must be below the lower lip in order to depress it, so you can quickly guide them to the right place to find it.
This is a tutorial on the muscles of the face, so the muscles responsible for facial expression. These muscles are innervated by the seventh cranial nerve, the facial nerve. When you’re testing a person’s cranial nerves and you get to cranial nerve no. 7, you ask them to wrinkle their forehead, to close their eyes as tightly as they can, to show you their teeth by making them smile and asking them to puff their cheeks out. This is a crude test of the muscles of facial expression.
The way I’m going to do this tutorial is that I’m going to start superiorly and work through the various muscle groups in the face – the orbital muscle group, the nasal muscle group and then the muscles in the oral region.
To begin with looking at the superior muscle on the face, you can see this muscle here, which is the frontal belly of the occipito-frontalis muscle. It’s called the ‘occipitofrontalis’ muscle because it consists of two muscle bellies. You’ve got the occipital muscle belly, so called because it’s on the occipital region of the skull and you’ve got the frontal belly of the occipitofrontalis.
Connecting these two muscle bellies, you’ve got this flat tendon sheath, this aponeurosis. If you have covered the layers of the scalp, you’ve been told that the aponeurosis of the occipitofrontalis makes up the third layer of the scalp. You’ve got skin, connective tissue, aponeurosis, loose connective tissue and then the periosteum. The aponeurosis of the occipitofrontalis is the third layer of the scalp.
If we just look at the orbital region, we can see these muscles which surround the eye. This muscle is called the orbicularis oculi. It acts sort of as a sphincter of the eye. You’ve got an outer part and inner part to this muscle.
This outer part here is called the orbital part and it’s responsible for closing the eyelids forcefully. If we just zoom in a little bit more, you can see the inner part of the orbicularis oculi. This is called the palpable part. It resides inside the eye and it’s responsible for closing the eyelid gently. That’s the orbicularis oculi, this circular muscle responsible for closing the eyelids.
The next muscle is this muscle here, the corrugator supercilii. It lies just deep to the orbicularis oculi and it draws the eyebrows medially and downward.
There are three muscles associated with the nasal muscles of the face in the nasal group. You’ve got the procerus, you’ve got the nasalis, which consists of a transverse part and then alar part and you’ve got this muscle in the midline which is called the depressor septi nasi.
The procerus muscle here on either side originates on the nasal bone and inserts onto the skin of the forehead. This muscle is active when an individual furrows.
These muscles here, the nasalis which consists of the transverse part and the alar part is responsible for compressing and flaring the nostrils, the nares. The transverse part compresses the nostrils and the alar part of the nasalis helps to flare the nostrils. It opens them out.
And this muscle here, the depressor septi nasi, the name kind of gives away what it does, it depresses the nasal septum. It draws the nose down inferiorly. It actually inserts onto the nasal septum and it assists the alar part of the nasalis in widening the nostrils.
Those are the three muscles of the nasal group of the facial muscles – the procerus, the nasalis and the depressor septi nasi.
The next group of muscles is the oral group of muscles. As you can see, there are quite a lot of muscles which make up this group. If you’re not interested in learning about all those in detail, then I’ll just cover the two muscles that you need to know, and then you can switch off after that. And then if you’re interested, you can carry on listening to find out about the other muscles.
What you need to know in the oral group if you only are going to learn two muscles is that there’s this big muscle here, which forms a circle around the mouth. This is known as the orbicularis oris. Just like you’ve got the circular muscles around the eyes, the constrictor on the eyes, the orbicularis oculi, you’ve got the orbicularis oris.
In Latin, oculus is an eye and os oris is a mouth. Orifice, oris help you to remember that. Orbicularis oris circle the mouth. It’s a circular muscle which circles the mouth. And you can kind of guess what the function is. When it contracts, it narrows the mouth and closes the lips. You get this pursing action, which you get when you’re whistling. That’s brought about by this muscle, the orbicularis oris.
And the other muscle you’ll need to know, which lies deep to these muscles here is the buccinator. This muscle is a muscle that forms the muscular component of the cheek. This is used when you’re puffing out your cheeks and blowing air out of your mouth. When you’re testing the patient’s seventh nerve and you ask them to puff out their cheeks, you’re testing the function of the buccinator muscle.
if you have to just remember four muscles from this tutorial, then try to remember these ones, the occipitofrontalis (which I showed you at the beginning with its occipital and frontal bellies), the orbicularis oculi (which closes the eyelids), the orbicularis oris here (which purses the lips, closes the mouth) and the buccinator (which is the muscular component of the cheek wall and which is used for forcefully expelling air from the mouth).
Now I’m just going to cover the remaining muscles in the oral group of the facial muscles. I’ll break it down into an upper group and a lower group.
Starting laterally, we’ve got the right risorius. Just by looking at where the muscle inserts, you can get an idea of what the function of that muscle will be. You can see that the risorius inserts onto the corner of the mouth. When it contracts, it will retract the corner of the mouth along this direction. That’s the risorius and you’ve got these muscles on both sides just (so just that you’re aware of that).
Moving superiorly, we’ve got the zygomaticus major. And again, looking at the point of insertion, you can see that when this muscle contracts, it will draw the corner of the mouth in an upward and lateral direction.
And just adjacent to the zygomaticus major, you’ve got the zygomaticus minor. What this muscle does is it inserts onto the upper corner of the mouth and it draws the lip upwards.
Next, we’ve got the levator labii superioris. And again, the name of this muscle indicates what the function and where it inserts. ‘Levator’ means elevator/lifter, ‘labii’ is Latin for lips and ‘superioris’ means upper, so it’s the lifter of the upper lip. Immediately, it tells you what the muscle function is.
And if we just look a bit closer, we can see the muscle that lies underneath it. This is the levator anguli oris. Remember, ‘oris/orifice’ refers to the mouth, ‘anguli’ means corner in Latin, so it’s the lifter of the corner of the mouth. It raises the corner of the mouth.
And just medial to that, we’ve got levator labii superioris alaeque nasi. Now that’s a really long name and it’s just Latin. It means lifter of the upper lip and of the alar cartilage of the nose. ‘Labii’ is lips, ‘superioris’ is upper, ‘alaeque’ means and of the alar cartilage and ‘nasi’ means of the nose. This has the function to lift the upper lip and it also opens the nostril, the alar cartilage part. That’s quite a long one to remember.
just to quickly go over those ones, you’ve got the risorius here (which is lateral and it inserts onto the corner of the mouth and which retracts the corner of the mouth), you’ve got the zygomaticus major and minor and then you’ve got the levator labii superioris and the levator anguli oris.
Just moving on to the lower group of oral muscles. There are a fewer muscles. If you just replace ‘levator’ with ‘depressor’, you essentially get the muscle names for this group of muscles.
Laterally, you’ve got depressor anguli oris. if you remember the Latin, ‘anguli’ means corner, ‘oris’ refers to mouth and ‘depressor’ obviously means it depresses, so it depresses the corner of the mouth. This is the most superficial muscle of the lower group of oral muscles and it depresses the corner of the mouth.
Just moving slightly medially, we’ve got depressor labii inferioris, the counterpart to levator labii superioris. This muscle depresses the lower lip. Again, Latin ‘depressor’ means depressor, ‘labii’ means lip, ‘inferioris’ means lower. What this muscle does is it depresses the lower lip and the direction of the fibers means that it also moves it laterally as well. That’s just deep to the depressor anguli oris.
And then deep to this muscle, the depressor labii inferioris, you’ve got the mentalis muscle. What this muscle does is it helps to position the lip for instance, when you’re drinking from a cup or something like that.
Those are the muscles of the oral group of the mouth. There are a lot of muscles and the names are quite long and complicated and if you just try to memorize them off by heart, it becomes quite hard, so that’s why I tried to explain to you the meaning of the names because if you think about that, it’s actually quite simple. If you think of the corner of the mouth, anguli. If you think of the position, which lip is it moving, upper or lower (so it would either be superior or inferioris) and if you think of the action of the mouth, depressor (if it’s on the lower part because it’s depressing it) and levator (if it’s on the upper part and it’s elevating it).
Those are all the muscles which are involved in producing movements of the mouth, the oral group of muscles.
The final muscle group to talk about is this muscle around the ear. These are the auricular muscles. You’ve got three muscles. You’ve got the auricularis posterior, the auricularis superior and the auricularis anterior.
Their function is pretty evident from their position. The posterior muscle pulls the ear backwards, the superior muscle elevates the ear and the anterior muscle pulls the ear upwards and forwards. Those are the auricular muscles.
Just to quickly recap, muscles of facial expression, you’ve got the occipitofrontalis with its two bellies, occipital and frontal bellies and then you’ve got other muscles of the face, which can be broken down into the orbital group, the nasal group and the oral group.
If you’re just going to remember four muscles, remember the occipitofrontalis, the orbicularis oculi, the orbicularis oris and the buccinator. And just remember when you’re remembering any muscles, just trying to think of what the name means, what the words actually means because they generally help you to remember the position and the function of the muscle.
That’s the muscles of facial expression.