The primary function of the frontalis branch of the facial nerve is to innervate the frontalis muscle, enabling the raising of the eyebrows and wrinkling of the forehead skin.
The frontalis muscle, located in the forehead, does not have bony attachments. Instead, it connects to the galea aponeurotica (a fibrous sheet connecting the frontalis and occipitalis muscles) superiorly and blends with the muscles around the eyebrows (orbicularis oculi and corrugator supercilii) inferiorly. This unique attachment allows the frontalis muscle, when stimulated by the frontalis branch of the facial nerve (cranial nerve VII), to elevate the eyebrows and create transverse wrinkles on the forehead.
Because the frontalis muscle is innervated by the facial nerve, damage to this nerve or its frontalis branch can result in paralysis of the frontalis muscle. This paralysis manifests as an inability to raise the eyebrows on the affected side, leading to a drooping or flattened appearance of the forehead and brow. This is important clinically when considering nerve damage from trauma, surgery, or certain neurological conditions.
In summary, the frontalis branch of the facial nerve plays a crucial role in controlling facial expressions by innervating the frontalis muscle, which is responsible for raising the eyebrows and wrinkling the forehead.
