 In this video, I will identify the axial muscles of the cephalic region and list the origin, insertion, and action of the major muscles in the cephalic region. We'll start by getting oriented to the location of the muscles in the cephalic region by first focusing on muscles of facial expression. Starting here, we'll look at the occipitofrontalis, a muscle that's located on the superior surface of the cranium. Occipitofrontalis has two bellies, two muscular compartments, a frontal belly located on the anterior, just superficial to the frontal bone. And the occipitofrontalis also has an occipital belly, and the occipital belly is located on the posterior, just superficial to the occipital bone. Now the two bellies of occipitofrontalis are both connected to a broad tendon located on the superior surface of the cranium known as the epichranial aponeurosis. And so the term aponeurosis means a broad tendon, and epichranial refers to its location on the superior surface of the cranium. So when the occipitofrontalis contracts, the action of this muscle is to furrow the eyebrow to wrinkle the skin in the frontal region on the anterior of the cranium. Next we'll look at orbicularis oculi. Orbicularis refers to the circular fascicle arrangement of this muscle, and oculi refers to its location surrounding the ocular region. The action of orbicularis oculi is to close the eyelids, and the eyelids are also known as palpebre, so orbicularis oculi closes the palpebre or eyelids in order to protect the anterior surface of the eye. Orbicularis aureus is another circular muscle with a circular fascicle arrangement, and orbicularis aureus is surrounding the entrance to the oral cavity, and the action of orbicularis aureus is to close the lips in order to protect the entrance to the oral cavity. The buccinator is a muscle located in the buccal region, that is in the lateral wall of the oral cavity, commonly referred to as the cheek. The buccinator, when it contracts, its action is to compress the cheeks, to compress the lateral walls of the oral cavity, and that action is important for sucking or blowing, for example, when you suck through a straw or to purse the lips to pucker up for a kiss. Or another action to blow through an instrument, for example, when playing the trumpet, you would need to compress your lips in order to form the lips into a shape for buzzing in order to produce the sound in the trumpet, and buccinator literally translates to the trumpeter because this muscle is important for buzzing your lips when playing the trumpet. Now here we have the same illustration from the textbook that I have added some labels to for us to identify a few more muscles of facial expression. We'll start with depressor labiae inferioris. Now this muscle tells you its action in the name. Depressor labiae inferioris, its action is to depress the lower lip. You can see it's located just inferior to the lower lip with its origin attached to the body of the mandible, and it inserts onto the lower lip. So a muscle that has the opposite action to depressor labiae inferioris, we see here is the zygomaticus minor. Zygomaticus minor elevates the upper lip, and then here we can see zygomaticus major is just a little bit larger than zygomaticus minor, and is located lateral to zygomaticus minor. Zygomaticus major inserts onto the corner of the mouth, onto the angle of the mouth in order to have the action of elevating the angle of the mouth, and this is what we commonly refer to as smiling. So zygomaticus major is your smiling muscle, and opposite to zygomaticus major is the depressor anguli oris. Depressor anguli oris, its action is in the name, it depresses the angle of the mouth, commonly referred to as frowning. Now we'll go through a little more detail with the origin insertion and action of major muscles, zygomaticus major and depressor anguli oris. Zygomaticus major has its origin from the temporal process of the zygomatic bone, and its insertion on the corner of the mouth in order to perform the action of smiling. Depressor anguli oris has its origin from the body of the mandible, and its insertion into the corner of the mouth to have the action of frowning. Now I'll go through the eye muscles. We'll start here with the levator palpebrae superioris. Levator palpebrae superioris has an action that's opposite to orbicularis oculi. Levator palpebrae superioris opens the eyelids. Next we'll move on to the extrinsic eye muscles or extraocular muscles that are responsible for directing the gaze. We'll start here with superior rectus. The superior rectus will direct the gaze upward or superiorly, and the opposite muscle inferior rectus directs the gaze downward or inferiorly. Then there are also medial rectus and lateral rectus, and so the medial rectus directs the gaze towards the midline and lateral rectus directs the gaze away from the midline or laterally. When you are looking at an object close to your face, the medial rectus muscle for each eye will contract to direct the gaze towards the midline, helping you to focus on an object closer to your face. And to direct the gaze further away, the lateral rectus muscles would direct the gaze away from the midline. If you are to look at an object on the right side of your face to direct your gaze to the right, you would contract the lateral rectus of your right eye and the medial rectus of your left eye. And to direct your gaze to the left side, you would contract the lateral rectus of your left eye and the medial rectus of your right eye. Last year we see the oblique muscles, the superior oblique. The superior oblique, when it contracts, it will direct the gaze downward and away from the midline, so the eye will roll to direct the gaze laterally and inferiorly. And so the inferior oblique will direct the gaze upward and laterally, that is direct the gaze superiorly and laterally. So notice that while the superior oblique directs the gaze inferior, the inferior oblique directs the gaze superior, but both the superior oblique and the inferior oblique direct the gaze laterally. Next we'll move to the muscles of mastication, muscles responsible for moving the mandible in order to chew. The temporalis is a large muscle that's covering the temporal bone as well as a portion of the parietal bone on the lateral aspect of the cranium. And the action of temporalis is to elevate the mandible, for example when you take a bite, that's what you're doing, you're elevating the mandible. And the masseter is another muscle that's important for elevating the mandible. You can see there that the masseter is located superficial to the buccinator in the buccal region. And now deep to the masseter, we can see the pteragoid muscles. And while the medial pteragoid muscle is a synergist with the temporalis and masseter for elevating the mandible, the lateral pteragoid is one of the muscles that's involved in depressing the mandible when you open the jaw. So the masseter has its origin from the zygomatic arch. The zygomatic arch is the temporal process of the zygomatic bone as well as the zygomatic process of the temporal bone. Then the insertion of the masseter is onto the ramus of the mandible. Together that orientation enables the masseter to perform the action of elevating the mandible. The temporalis has its origin from the temporal line, which is along the parietal bone and temporal bone primarily, but it does extend slightly onto the frontal bone as well. And so along the lateral aspect of the cranium, this prominent ridge, the temporal line serves as the origin for the temporalis. Then the insertion of the temporalis is the coronoid process of the mandible, and then the action is to elevate the mandible. Next we'll move to the extrinsic tongue muscles, muscles that are responsible for moving the tongue, but they're the extrinsic muscles because they have an origin from outside of the tongue and their insertion is into the tongue. Stylo glossis, its name tells us its origin and insertion. Stylo for the styloid process of the temporal bone and glossis means tongue. So stylo glossis, its action is to retract the tongue and can also elevate the tongue. Stylo glossis retracts the tongue, whereas genioglossis protracts the tongue. So to stick the tongue out, to protract the tongue, genioglossis contracts. Genioglossis refers to the origin on the chin from the deep surface of the body of the mandible, and then glossis again referring to tongue, the genioglossis when it contracts protracts the tongue. So the action of genioglossis is the opposite of the action of stylo glossis, stylo glossis retracts and genioglossis protracts. Then hyoglossis with its origin from the hyoid bone inserting into the tongue performs the action of depressing the tongue and would also synergize with stylo glossis as assisting in the action of retracting the tongue. So stylo glossis has its origin from the styloid process of the temporal bone, its insertion into the tongue, and the action of stylo glossis is to retract the tongue.