Movements come about because muscles or muscle groups contract. When a muscle contracts, the distance between the two points of attachment of that muscle becomes shorter. Because the attachment points are mostly bone pieces, two things can happen:
- The bone pieces come closer together.
- The mutual position of the bone pieces changes.
The attachment points of the muscles have special names. The origo of a muscle is the point of attachment of the muscle to the least mobile bone. The insertion of a muscle is the point of attachment to the most mobile bone.
The group of chewing muscles consists of four muscles. They move the lower jaw when they chew and speak to the skull. The four chewing muscles are:
- The musculus masseter. The m. Masseter has its origin on the yoke arch, or arcus zygomaticus. It runs from the yoke arch on the outside of the mandibula to the jaw angle, or angulus mandibulae, and the corpus mandibulae. The m. Masseter is a strong muscle. It helps to close the mouth and determines the chewing pressure.
- The temporalis musculus. The temporalis m is a fan-shaped muscle and has the os temporal as an origo. He walks past the cheek arch to the lower jaw. The insertion is the coronoid process. When tightened, the temporalis m pulls the lower jaw up, thereby closing the mouth. Because a part of the muscle fibers on the back of the sleep runs back, the lower jaw is also pulled back.
- The pterygoideus lateralis musculus. The m. Pterygoideus lateralis is a short muscle. It runs from the sphenoidal bone to the condylaris process and the jaw joint. When tightened, the m. Pterygoideus lateralis pulls the lower jaw and the articular disc forward.
- The pterygoideus medialis musculus. The m. Pterygoideus medialis has the os sphenoidal and the maxilla. From here he walks to the inside of the lower jaw to the angulus mandibulae. If the m. Pterygoideus medialis contracts, the mouth closes. The lower jaw and the articular disc also move forward.
These muscles ensure that the lower jaw is pulled against the upper jaw. In addition, they ensure that the lower jaw can slide in all directions while chewing (see image below).
The group of suprahyoidal muscles has in common that all four muscles have the tongue bone or hyoid as an insert. From the tongue bone they walk to the skull; they are, so to speak, above (= supra) the tongue bone. These muscles have two functions.
- When they tighten, the position of the tongue bone relative to the mandibula and the rest of the skull changes. This is how the tongue changes.
- If the tongue bone does not change location during contraction, the mouth will be opened. The muscles pull the lower jaw towards the tongue bone (see image below).
Three muscles from the suprahyoidal muscle group are called the mouth floor muscles:
- The mylohyoid muscle. This is the largest oral floor muscle. He runs diagonally backwards from the inside of the lower jaw, to the tongue bone, the ox hyoid. The mylohyoid forms a v-shaped plate within the lower jaw.
- The geniohyoid muscle. The muscle runs from the inside of the lower jaw (at the height of the chin) to the tongue bone. He walks over the mylohyoid.
- The digastricus musculus. The muscle is attached to the tongue bone in the middle by a tendon. This creates two narrow sections that can move independently of each other: a front section and a rear section. The digastricus m runs from the inside of the lower jaw (at the height of the chin) to the tongue bone. The posterior part runs from the temporal bone to the tongue bone (see image below).
The tongue is an organ that for the most part consists of muscles. A part of the tongue muscles lies entirely within the tongue. Another part of the muscles enters the tongue from outside. We can therefore divide the muscles of the tongue into intrinsic tongues muscles, that is to say the muscles that lie entirely within the tongue body, and extrinsic tongues muscles, ie the muscles that run into the tongue from outside.
The intrinsic tongue muscles run in three (main) directions within the tongue body.
- The muscles that run from front to back make the tongue shorter. Because the tongue becomes shorter, it also becomes wider and thicker.
- The muscles that run from left to right make the tongue narrower. Because the tongue becomes narrower, it also becomes higher and longer.
- The muscles that run from top to bottom make the tongue thinner. Because the tongue becomes thinner, it also becomes longer and wider.
The intrinsic tongue muscles have no origo or insertion, they lie entirely within the tongue.
The function of the intrinsic tongue muscles is to determine the shape of the tongue during the chewing process and also while speaking.
The extrinsic tongue muscles are the muscles that all enter the tongue body from the outside. Because these muscles come from different sides, they can move the tongue in all kinds of directions: forwards, backwards, upwards, left and right. The largest extrinsic tongue muscle is the genioglossus musculus. He has his origo on the inside of the lower jaw (at the height of the chin) and runs into the tongue (see image below).
The infrahyoidal muscles are the muscles that have the os hyoid as an insert, but run on the underside of the tongue bone. This is in contrast to the suprahyoid muscles, which run on the upper side of the tongue bone. The origin of the infrahyoid muscles lies in the shoulders and neck. They serve as auxiliary muscles in the swallowing process and indirectly contribute to bending the neck (see image below).
The mimic or facial muscles are the muscles that have a function in moving the superficial parts of the face. Humans have many mimic muscles. We can give different expressions to our face. These facial expressions differ from person to person. This is not only because everyone has a different skull shape, but for the most part because the patterns of contraction of the mimic muscles are different in every person.
Two of the mimic muscles play an important role in the functioning of the mouth in the chewing process and in speech:
- The musculus buccinator is the muscle that runs through the cheek (= bucca);
- The musculus orbicularis oris is the orbicular muscle around the mouth (see image below).
Neck and neck muscles
The neck and neck muscles mainly ensure the movements of the head as a whole. The head can be moved forwards, sideways and backwards and moreover the head can turn. Maintaining the posture of the head is also a function of the neck and neck muscles. In many situations the posture of the head must be maintained for a long time (see image below).