The frontalis muscle, or forehead muscle, is part of the occipitofrontalis muscle. Its function is essentially to raise the eyebrows and frown; thus, it contributes to facial expressions and thus nonverbal communication. Stroke, triggered by insufficient blood supply to the brain, can result in temporary or permanent paralysis of the frontalis muscle.
What is the frontalis muscle?
The frontalis muscle lies under the skin of the forehead. It is part of the occipitofrontalis muscle, which also includes the occipitalis muscle, located at the back of the head. Musculus frontalis and Musculus occipitalis are connected longitudinally across the skull. The German name for the frontalis muscle is the forehead muscle or, according to one of its functions, the eyebrow elevator. The occipitalis muscle has the opposite effect: it smoothes the forehead. Physicians also refer to the muscles working together as the bellies of the occipitofrontalis muscle.
Anatomy and structure
The frontalis muscle arises from the cephalic fascia at the forehead and attaches to the galea aponeurotica, which connects it to the occipitalis muscle. When viewed in cross-section, the frontalis muscle lies between two layers of tissue: the skin and the fascia, a soft part of the connective tissue. Muscles that lie between these two layers are also called cutaneous muscles. In humans, this group of striated (skeletal) muscles only plays a major role in facial expressions; animals sometimes use sudden twitches of the skin muscles specifically to scare away insects. Skin muscles are located not only in the face, but also in other regions of the body.
Function and tasks
Tension (contraction) and relaxation (relaxation) of the frontalis muscle contribute to facial expressions, which, as nonverbal communication, play a major role in social processes. Among other things, the frontalis muscle is involved in the expression of two basic emotions: Anger and Surprise. Together with joy, fear, sadness, contempt and disgust, they form the seven basic emotions according to Ekman, which all people across cultures can spontaneously show and recognize. Social scientists and psychologists therefore also refer to them as universal emotions or basic emotions. When showing anger, the frontalis muscle triggers a frown that draws the eyebrows together and forms wrinkles on the forehead. This causes the brows to tilt downward more on the inside than on the outside. If, on the other hand, a face expresses surprise, the eyebrows lift and usually acquire a stronger curvature than in the relaxed state. For the objectified examination of emotional facial expressions, the Facial Action Coding System (FACS) records patterns of muscle contraction and relaxation and assigns them to the respective underlying emotions. The FACS detects even weak unintentional activity of the facial muscles. The frontalis muscle and the superior unit of the occipitofrontalis muscle also indirectly support the protection of the eye as well as its direction of gaze. The human eye is a complex lens system that is very sensitive to irritation. Excessive light and inadequate stimuli (for example, swirling sand) can be equally damaging to the visual organ. The eye socket shields the eyeball to some extent, but is not sufficient as the only protective mechanism. When very strong light falls on the retina, people react reflexively with a series of defensive movements: They squint their eyes, turn away if possible, use their hands to shield their faces if necessary – and frown. Contraction of the frontalis muscle pulls the eyebrows together and causes a slight bulge over the eye area. This makes it harder for ambient light to enter the eye and reach the retina.
Diseases
Paralysis of the frontalis muscle can occur as a result of a stroke (apoplexia cerebri or apoplexy for short). Also known as cerebral apoplexy, this neurologic disease results from inadequate blood supply to the brain. The possible causes of this undersupply are manifold: blood clotting disorders, thrombosis, damage to the vessel wall (for example, ruptures) with subsequent blood loss, convulsions and bleeding in the brain are among the most common. Musculus frontalis and other muscles may be permanently or temporarily damaged and may be both completely and only partially paralyzed.In addition, mere weakness of the facial muscles is possible; however, it is also not present in every stroke. Which symptoms manifest themselves depends on which part of the brain is undersupplied. Typical signs include dizziness, nausea, vomiting, visual disturbances, balance problems, headaches, numbness, and gait disturbances. Some patients exhibit poor temporal and/or spatial orientation or are unable to give information about themselves. Functional language impairments involving comprehension, word finding, or other areas of language may also occur. In addition, people with apoplexy often appear generally confused. Signs of stroke absolutely demand immediate evaluation by trained professionals. For accurate diagnosis, doctors usually resort to computed tomography (CT) or other imaging techniques. The scan makes the structure of the brain visible and thus allows possible hemorrhages or abnormalities to be precisely localized. In individual cases, the treatment also depends on the cause, which in most cases is initially mainly medication. In the long term, patients after a stroke also benefit from rehabilitative measures that can potentially improve individual secondary symptoms.
