[Biology Class Notes] on Masseter Muscle Pdf for EXAM

The word masseter was originated from the Greek word masasthai which usually means the act of chewing something. It is a very noticeable and prominent jaw muscle. The muscle starts from the cheekbone or the zygomatic bone. Further, it is pushed into the rear side of the jawbone or mandible. The muscle is used mainly while we chew food as the muscle contracts itself and the mandible rises. If you start clenching your teeth, you can feel the masseter near the side of the jaw. One of the major mastication muscles is the masseter as per human anatomy. Especially in herbivores it has a much stronger structure and helps in plant matter chewing. It is mostly found in mammals. The masseter muscle is one of the strongest and superficial ones amongst all other mastication muscles.

The Masseter Muscle Structure

The masseter muscle is a quadrilateral and mostly thick muscle. It is deep and superficial which consists of two particular heads. At the junction of the insertion, the fiber material of the two separate heads becomes continuous. First, we will discuss the superficial head of the mandible muscle. Usually, the superficial head starts from the tendon-like, thick sheets of fibrous white tissue known as aponeurosis that usually helps in the attachment of sheet muscles and requires a broad area. It comes from the temporal region of the cheekbones or zygomatic bone. It is a large structure and also comes from the zygomatic arch’s two-third portion near the inferior border mainly on the anterior side. The mandible ramus’s lateral surface has an inferior half which cuts out a certain angle with the mandible. All the fibers coming pass into this section both posterior and inferior. 

Next, we have the deep head which is a much more muscular part of the mandible muscle and it is also much smaller in size. The zygomatic arch’s middle surface entirely gives rise to the deep head along with the lower border’s posterior third portion. The fibers run forward and downward and are finally pushed into the ramus’s upper portion. It remains as high as the mandible’s coronoid procedure. The anterior portion of the muscle of the deep head is partially concealed from the superficial position. The parotid gland covers are posterior. 

Innervation of the Masseter Muscle

Total we have four muscles of mastication. They include the masseter, the medial pterygoid, temporalis, and the lateral pterygoid. All these muscles are usually innervated. Similarly, the masseter is also anteriorly divided. The trigeminal nerve has got a mandibular division which is further anteriorly divided. The innervation pathway starts with the gyrus precentralis followed by the genus capsula interna. It is then followed by the nucleus motorius Nervi trigemini and nervus trigeminus. Lastly, we have the nervus mandibular and finally arrive at the musculus masseter.

Function of the Masseter Muscle

The main masseter muscle function is to chew food. For herbivores, it is specifically strong and larger for chewing and extracting nutrition from plants. The mandible is automatically elevated and raised when the entire mandible muscle goes through a bilateral contraction. It in turn raises the lower jaw. As the jaw closes, the mandible elevation occurs. The muscular structure of the medial pterygoid is simultaneously very much similar to that of the masseter muscle. But again it is much stronger. The protrusion can also be caused by such superficial fibers.

Examination of the Masseter Muscle 

Now that we have studied the masseter muscle function, let us quickly take a look into the examination procedure for an extra-oral test. The first thing is to stand near the patient-facing difficulties and inspect everything visually. After that, the muscle needs to be palpated bilaterally. As the patient continuously clenches their teeth for a long time and several times. When the patient does this, fingers on both of your hands should be already placed over the muscles. Hence, the entire process of examination of the masseter muscle is pretty easy and simple. It does not require much test equipment.

Did You Know?

• It is often known as the strongest muscle based on its weight.

• Putting or pushing your fingers slightly into the sides of your jaw can instantly relax the masseter muscles.

• If suddenly one day you wake up and find a strange square shape of your face, then be sure that the masseter muscle has enlarged.