The muscles of the head essentially have the function of facial expression and chewing. Therefore, we differentiate the chewing musculature and the mimetic musculature.
The Chewing Musculature
The chewing muscles, in the narrower sense of the word, are supplied by the motor portion of the trigeminal nerves. The cheek muscle or chewing muscle (musculus masseter) is among the chewing muscles, which has its origin at the zygomatic bone and is attached to the mandibular angle. The powerful temporal muscle (musculus temporalis) is situated fan-shaped on the sidewall of the skull, and ensures that the joint of the jaw closes. The latter produces approximately 50% of the chewing power. The cheek muscle and temporal muscle generate the chewing pressure and are responsible for the biting movements. The interior and exterior wing muscle (M. pterygoideus lateralis and M. pterygoideus medialis) are among the chewing muscles. They allow the jaw to do such things as rotational and grinding movement. The exterior wing muscle pulls the lower jaw forward, thus controlling the movement of the jaw opening. It is supported in this process by the upper hyoid bone musculature (suprahyale muscles).
The Mimetic Musculature
The facial muscles are far under the skin. This means that they are mostly composed of thin muscle fiber plates. They are directly below the subcutaneous fatty tissue. In contrast to the skeletal muscles, they are stretched directly between the skin and bones, which means that they do not have any connective tissue envelope (Fascie).
When it contracts, the skin is moved back and wrinkles form. This means that they do not move any bones. They open and close the mouth and the palpebral fissure. They move the nostrils, the scalp and the ears to a certain extent.
The facial musculature is also designated as the mimetic musculature. It has an influence on the facial expressions so that we can make conclusions on a person's mood from his or her facial expression. This peculiarity is even greater with children. Adults have more or less learned to control themselves.
The mimetic muscles are supplied by the VII cranial nerve (N. facialis).
The orbicularis oculi muscle (M. orbicularis oculi) is in the arch around the skin of the eye and the lid. It is responsible for closing the lid and its outside portion for the eye winking. If the eye muscle is paralyzed, the eye cannot be completely closed and there is the danger that the conjunctiva will dry out.
The muscle for the bridge of the nose (M. proceus) produces transverse wrinkles in the skin of the bridge of the nose (”wrinkling your nose”). The nostril levator (M. levator labii superioris alaeque nasi) opens up the nostrils. The nose muscle (M. nasalis) surrounds the nostrils and pulls the soft parts of the nose downward, this closing the nostrils somewhat.
The orbicularis ori muscle (M. orbicularis oris) surrounds the oral fissure. It forms and closes the mouth. If this muscle contracts strongly, it can push the mouth towards the front in the shape of a trunk. If it only contracts weakly, the lips are on top of one another.
The cheek muscle (M. buccinator) holds the food between the teeth when chewing. It also makes it possible to blow air out of the mouth ("the trumpet muscle"). The zygomatic bone muscle (M. cygomaticus) pulls the angle of the mouth backwards and upwards. It is the ”laughing muscle” and it is responsible for dimples. In contrast, the triangular muscle (M. depressor labii inferioris) pulls the angle of the mouth downwards and gives the face a disdaining expression.
The chin muscle (M. mentalis) pushes the lower lip forwards and
produces the dimple in the chin. Temporal (M. occipitofrontalis) and
occipital muscles (M. epicranius) share in mimetic musculature. The
so-called galea, a tendonous plate, lies between them.
