The occipitofrontalis muscle is a cutaneous muscle composed of the occipitalis muscle and the frontalis muscle, which belongs to the mimic musculature. The muscles raise and lower the eyebrows to frown or tighten the forehead. In lesions of the facial nerve, paralysis of the occipitofrontalis muscle occurs.
What is the occipitofrontalis muscle?
The musculi epicranii is a muscle group known as the occipitofrontalis muscle, which is part of the mimic musculature and is closely attached to the skull. The insertion of the muscle group is located at the galea aponeurotica. Different muscles belong to the Musculi epicranii, for example the Musculus frontalis and the Musculus occipitalis. The former is a cutaneous muscle. Together with the occipitalis muscle, it is called the occipitofrontalis muscle or, in German translation, the occipitofrontal muscle. The two muscles are innervated by the facial nerve, which controls all the muscles of facial expression. The two bellies of the occipitofrontalis muscle are located at opposite cranial poles. The galea aponeurotica provides the connection between the two parts. Synonymous terms for the two muscle bellies of the occipitofrontalis muscle are the expressions venter frontalis and venter occipitalis.
Anatomy and structure
The venter frontalis takes its origin at the margo supraorbitalis of the frontal bone and near the glabella. The muscle radiates fiber tracts into the mimic musculature of the immediate vicinity and is thus associated with the procerus, corrugator supercilii, and orbicularis oculi muscles. The opposite pole muscle belly of the occipitofrontalis occipitalis muscle takes its origin at the linea nuchae suprema of the os occipitale and proportionally at the os temporale. Both muscle bellies send their fibers vertically in a cranial direction to radiate into the tendon plate of the cranial vault. At this galea aponeurotica they find common attachment. Each of the muscle bellies has an almost quadrangular plan. However, the venter frontalis becomes more pronounced and shows longer fibrous tracts. Like all skin muscles, the frontalis muscle in particular lies between the fascia and the skin. The frontal venter is motorically innervated by the rami temporales of the facial nerve. For the venter occipitalis, the posterior auricular nerve of the facial nerve provides innervation.
Function and Tasks
Like all mimic muscles, the occipitofrontalis muscle is involved in human facial expressions. Facial expressions possess expressive and communicative value for humans. Compared with linguistic communication, mimic communication corresponds to a more primal and relatively overlapping form of communication. Even infants are capable of interpreting mimic signals. This connection confirms the genetically deep roots of mimic communication. Far before language existed, humans were already capable of self-expression thanks to the mimic form of expression. Moreover, mimic expression is characterized by far fewer cultural differences than speech expression. During verbal communication, people receive clues about the actual emotional state of their interlocutor through minute movements of facial expressions. Many mimic movements are almost automatic and thus ‘reveal’ what is verbally withheld. Like every mimic muscle, the occipitofrontalis muscle thus assumes communicative and expressive functions. The contraction musculus frontalis frowns and raises the eyebrows. Thus, the muscle is involved in the facial expression of doubt or incomprehension. Contraction of the occipitalis muscle smooths the furrowed brow and lowers the eyebrows. Thus, two antagonistic muscles of facial expression are combined as the occipitofrontalis muscle. While one of the muscle bellies tenses, the other must relax. The simultaneous contraction of both muscles is impossible. Since the occipitofrontalis muscle delivers individual fibers to other muscles of the facial expression, it is involved in other movements of the facial expression in the broadest sense. For example, due to its participation in the procerus muscle, individual fibers of the occipitofrontalis muscle are also involved in the expression of anger in the form of a frown line. In addition, fibers of the muscle in the orbicularis oculi muscle are involved in the distribution of lacrimal fluid. The occipitofrontalis muscle is called the skin muscle because its contraction ultimately moves the skin of the forehead.
Diseases
Like all other muscles, the occipitofrontalis muscle forms a neuromuscular unit with its supplying nerve. This nerve corresponds to several portions of the facial nerve, which distributes contraction commands from the central nervous system in the form of bioelectrical excitation to the two individual muscles. Damage to the nerve can impair the occipitofrontalis muscle and all other muscles of the mimic musculature in their work. Paralysis of the facial nerve can be preceded by congenital causes, but also by acquired causes such as fractures of the skull. Inflammatory causes such as otitis media, chronic meningitis or Lyme disease are also conceivable causes. Apart from these, tumors of the cerebellopontine angle and immunological processes such as Guillain-Barré syndrome, Heerfordt syndrome, or Melkersson-Rosenthal syndrome cause facial nerve palsies. Mild facial nerve palsies show only discrete symptoms. More severe paralyses result in changes in overall facial expression, so often with a lifted or weakened frown as well as incomplete eyelid closure and drooping corners of the mouth. Because the facial nerve sensitively innervates the tongue, taste disorders may also occur. Isolated paralysis of the occipital muscle has less effect on facial expression than isolated paresis of the frontalis muscle. Isolated paralysis of a single muscle belly occurs with localized damage to the facial nerve such as may result primarily from inflammation. Like any other muscle, the occipitofrontalis muscle can be affected by typical muscle diseases such as myopathies or atrophy. Muscle fiber tears and related phenomena are extremely rare in the mimic muscles.
