Muscles of Mastication – Facial Muscles

00:01 Now, we have the muscles of mastication.

00:04 And we have four pairs of muscles of mastication.

00:08 The first one highlighted in red here is the masseter.

00:13 The masseter is originating from the maxillary process of the zygomatic bone, as well as the zygomatic arch.

00:21 Its insertion is here to the ramus of the mandible.

00:27 All muscles of mastication will be innervated by branches of the trigeminal nerve, and the masseter is innervated by the masseteric nerve, the anterior trunk of the mandibular nerve, which is a branch of the trigeminal.

00:43 When the masseter shortens or tracks it's going to elevate the mandible, thus closing the jaw, and it can also produce some minor jaw protrusion.

00:54 So it can move the mandibular jaw outwards or forward just a little bit.

01:03 The temporalis is the next muscle of mastication and you see it highlighted in red.

01:11 It's originating from the floor, the temporal fossa in the overlying temporal fascia.

01:18 It's insertion is to the coronoid process and ramus of the mandible.

01:26 Temporal branches of the anterior trunk of the mandibular nerve serve as its innervation.

01:34 And when it contracts, it will elevate the mandible, thus closing the jaw, and the horizontal fibers are going to be primarily retractors of the mandible.

01:46 So they will pull the mandibular jaw inward.

01:56 Next, here we have the lateral pterygoid muscle.

02:00 And here we see the lateral pterygoid on the left highlighted in red.

02:08 Kind of has two points of origin from the skull: one, is from the infraotemporal surface and crafts to the greater wing of the sphenoid.

02:18 And then the other point of origin of the lateral pterygoid is going to be the lateral surface of the lateral pterygoid plate.

02:25 So hence its name because of this partial origin from the pterygoid plate.

02:32 Insertion is going to be on the joint capsule and articular disc of the temporal mandibular joint, or excuse me temporal mandibular joint, and it also has a partial insertion on the neck of the condyliod process of the mandible.

02:51 Innervation is by the lateral pterygoid nerve, which is from the anterior trunk of the mandibular nerve against, again a division that trigeminal.

03:02 And its action when it contracts is to protract the mandible, as well as to depress the chin.

03:11 It also produces lateral side to side movements of the jaw as well during chewing or mastication.

03:20 Lastly, we have another pterygoid muscle but this one is more immediately located, highlighted in red.

03:28 It has two points of origin.

03:30 One is from the medial surface of the lateral pterygoid plate and pyramidal process of the palatine bone.

03:37 It also has a point of origin from the maxillary tuberosity.

03:43 The insertion is to the ramus of the mandible.

03:49 And its innervation is the medial pterygoid nerve, which is a branch of the anterior trunk of the mandibular nerve.

03:57 And lastly, the action of the medial pterygoid when it contracts is to elevate the mandible and then produce protrusion of the mandible.