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Rega Anatomy 1.14.05 1PM Side A MSI


I知 going to be talking about muscles of mastication. You want to be careful about how you pronounce that; mastication is chewing; the temporal mandibular joints and the infratemporal fossa. We are going to differentiate this. I値l be talking in a little bit more detail about what constitutes mastication and what contributes to it, but we are going to consider the true muscles of mastication to be these four muscles; temporalis, masseter, the medial pterygoid, and the two parts of the lateral pterygoid. We値l talk about those in more detail. They have certain functions that we can group together and, primarily, we are going to think about the first three of these muscles as being jaw adductors princely. That is, strictly speaking, very true of 2 and 3. In other words, both the masseter and the medial pterygoid are balanced muscles that are going to hold the corner of your mandible in a sling and they are going to provide adduction of the jaw on essentially the same plane. Temporalis, as you値l see in lab today, is a little more complicated because it is a big fan-shaped muscle and so the degree of pull and what it will do to the mandible will change given the mandibles position. We are not going to break that down to finely, but realize that although temporalis we are going to primarily think of as a jaw adductor, there are certain fibers, particularly the cranial fibers of temporalis that can also act to assist in jaw opening. It is sort of counterintuitive until you actually see those fibers and see where the fulcrum of the joint is. Really though, I知 going to think about those for our purposes as adductors, whereas the lateral pterygoid; particularly the lower head, is going to act in a very different fashion and that is a direct reflection of the fact that its fibers are oriented almost horizontally. You値l see a number of things to reinforce that. Therefore, give the relationship between its origin on the pterygoid plate moving anteriorly towards the mandiblesorry, posteriorly toward the mandible, it is going to pull the mandible anteriorly and be a protractor. Now, realize that although these are the true muscles of mastication, there are accessory muscles. In other words, you cannot have normal chewing unless, for instance, your buccinator is functioning to kind of pinch itself out of the way or unless your tongue is moving the bolus of food around, unless your digastric is functioning properly in order to open your jaw to that phase of chewing and, certainly, one that is not on this list but is on the list in your handout, if your orbicularis aures muscle can稚 hold your mouth closed you are going to be drooling while chewing. All of those things are important for the process of mastication, but we do not consider them, anatomically, muscles of mastication