In the social interactions of our day-to-day lives, the frontalis muscle plays a major role. Since it is the only muscle that raises eyebrows, its function goes beyond simply keeping them out of one’s visual field; it is also necessary for conveying feelings and nonverbal communication. The frontalis muscle is antagonistic to the procerus muscle, the corrugator supercilii muscle, and the orbicularis oculi muscle.
The frontalis, corrugator, procerus, and orbicularis muscles all have cutaneous insertions and confluence at the glabella, and the orbital rim, where their respective movements and forces can lead to cutaneous rhytids (frown lines, smile lines, forehead lines, horizontal nasal lines). The position and shape of the eyebrows are determined by the balance between these muscles.
What is the Frontalis Muscle?
How well is your frontalis muscle working? The vast majority of people have no idea what the frontalis muscle is or where it is located. It’s located on top of your forehead.
You can test the functionality of your frontalis muscle by following these simple steps:
- Look for a mirror
- Stand in front of the mirror and look at your reflection
- with raised eyebrows
When you looked into the mirror while raising your eyebrows, did your forehead become wrinkled? Then your frontalis muscle seems to be working fine.
Frontalis Muscle: Definition
At the top of the skull (in the area of the forehead), the frontalis muscle is a thin, wide, four-sided muscle. Specifically, this muscle originates from the galea aponeurotica, extends down the forehead, and inserts or attaches to the skin around the eyebrows and the top of the nose. A sheet of fibrous tissue covers the top of the skull called the galea aponeurotica.
The frontalis muscle runs in the forehead, between the galea aponeurotica, the eyebrows, and the top of the nose.
Frontalis Muscle: Origin & Insertion
Though the frontalis muscle may appear to be an independent muscle, it is actually a part of a larger structure called the occipitofrontalis muscle or epicranius. SCALP is a useful acronym for remembering the layers of the scalp:
S: Skin
C: subcutaneous connective tissue
A: Aponeurosis (galea)
L: Loose areolar connective tissue
P: Periosteum
Rather than one muscle belly as the occipitofrontalis, it consists of two muscle bellies: the frontalis and occipitalis, which are connected and enclosed by a thick fascia called the epicranial aponeurosis or galea aponeurotica.
The occipital part of the occipitofrontalis muscle moves the scalp forward, while the frontalis part lifts the brows and moves the anterior scalp backward. The vertical fibers in the frontalis muscle pull the eyebrows upwards when it contracts.
The superficial musculoaponeurotic system (SMAS) continues above the zygomatic arch and includes the temporoparietal fascia (which blends with the galea) and frontalis muscle, as part of the SMAS.
The orbicularis oculi, corrugated, and procerus muscles act as antagonists to the frontalis muscle. There is no bony attachment to the frontalis muscle. The corrugator muscle lies below the frontalis and the orbicularis muscles and has a bony origin from the medial orbital rim.
Surface Anatomy
The frontalis muscle produces horizontal forehead lines. The types of forehead lines are as follows:
- Lines that run straight across the whole forehead (45%)
- Gullwing shapes with a central depression and lateral elevation (30%)
- There are a few or no horizontal lines lateral to the center of the forehead (10%)
- lateral straight lines forming two columns on the lateral aspect of the forehead with no central lines (15%)
Frontalis Muscle: Muscle Structure
The frontalis muscle is composed of vertical striations in a fan-like pattern. A muscle is sometimes divided into medial, intermediate, and lateral fibers clinically, despite no anatomical or histological distinction. From the galea aponeurotica, which corresponds with the hairline on the surface, it arises posteriorly.
On the inferolateral side, the muscle interdigitates with fibers of the procerus muscle, and on the inferomedial side, it has attachments to the orbicularis oculi and corrugator muscles. Generally, the frontalis inserts at the eyebrow dermis and terminates laterally at the temporal ridge, but there are exceptions, and the frontalis may sometimes terminate more medially as well.
Despite being a thin muscle with high vascularity, the bulk of it is located right above the brow. Laterally, it is thinnest, which is a sign of weakness and the first area to sag with age.
When measured from the supraorbital notch, the lateral extent of the frontalis muscle, where it interdigitates with the orbital orbicularis muscle, may be small, medium, or large. The exact distribution in the normal population is unknown.
When the horizontal frontalis is smaller, the lateral brow will have less support, leading to brow ptosis and lateral brow ptosis with secondary dermatochalasis in particular.
At 20%, the lateral-most extent of the frontalis muscle is asymmetric where it interdigitates with the orbital orbicularis muscle. Asymmetrical lateral brow ptosis and secondary dermatochalasis may result from this arrangement. Research has found similar variations in the length of the corrugator muscle as being short or long, although it revealed no differences in the procerus or orbicularis muscles.
According to research, the right belly of the frontalis muscle is significantly larger than the left side, although electromyographic studies have shown the muscles on both sides are equally active.
It is possible for the frontalis muscle to be confluent from right to left with no bifurcation (up to 45% of subjects). There will be a variable central bifurcation between the frontalis muscles in the rest of the exercises. It consists of connective tissue that bisects the galea aponeurotica, with varying widths from person to person.
In 15% of anatomical dissections, Abramo et al. found the complete separation of the frontalis muscle bellies with a central galeal aponeurosis.
A third of subjects have a gross asymmetry between the right and left frontalis muscle belly.
There is evidence that the angle between where the frontalis interdigitates with the orbital orbicularis muscle may be small, medium, or large, and that it may become smaller with age, causing further lateral brow ptosis and secondary dermatochalasis.
The lateral edge of the frontalis muscle may extend to the temporal crest, may extend beyond it, or may fall short of it.
Frontalis Muscle: Function
As you did at the beginning of this lesson, the frontalis muscle is responsible for raising the eyebrows and wrinkling the forehead. As the frontalis muscle inserts or attaches to the skin around the eyebrows, as this muscle contracts, the skin around the eyebrows is pulled upward which lifts the eyebrows.
For the frontalis muscle to function, it must receive electrical impulses from the brain through cranial nerve VII, a process known as innervation. Cranial nerve VII is also known as the facial nerve.
Remember the last time you were really surprised or scared. Possibly you were watching a scary movie or your friends and family surprised you on your birthday. How did your facial expression look when you were scared or surprised? Most people raise their eyebrows and wrinkle their foreheads when they are shocked or frightened. For this reason, the frontalis muscle is used to create these types of facial expressions.
The frontalis muscle lifts the eyebrows and wrinkles the forehead, which is a common expression of being shocked or scared.
Embryology
In addition to the other muscles involved in facial expression, the frontalis originates from the second pharyngeal arch, which forms between the third and eighth weeks of development.
The Blood Supply and Lymphatic System
Both the internal and external carotid arteries supply blood to the frontalis muscle. Upon exiting the orbit and traveling up the forehead, the supratrochlear and supraorbital arteries supply the muscle from the inferior margin. The supraorbital artery can exit through the supraorbital notch/foramen, while the supratrochlear artery exits more medially from the orbit.
They are both branches of the internal carotid artery, which is a branch of the ophthalmic artery. Following their respective exits, the supratrochlear and supraorbital arteries split further into superficial and deep branches.
The superficial vessels supply muscle, galea, and skin, while the deeper vessels supply the periosteum. The supratrochlear and supraorbital arteries supply most of the blood medially, while the frontal branch, which comes from the superficial temporal artery, supplies the blood laterally. Throat arteries form an anastomosis with one another to form a highly vascularized network.
The lymphatic drainage of the forehead is complex and poorly understood. According to studies on the drainage of the forehead, the lateral portions drain differently than the medial portions. Regardless, it appears that the forehead drains mainly into the preauricular nodes and parotid nodes.
Main venous drainage occurs between three veins: the supratrochlear vein is the most medial, followed by the intermediate supraorbital vein, and finally, the lateral frontal vein. A transverse vein that runs above the orbit further connects the three, appropriately called the transverse supraorbital vein.
The transverse supraorbital vein connects medially to the angular vein, which drains into the cavernous sinus and ophthalmic vein. Regarding the risk of external facial infections leading to potentially harmful intracranial infections or cavernous sinus thrombosis, it is important to remember this relationship.
Nerves
The muscles of facial expression are supplied with nerve fibers by the cranial nerve VII (the facial nerve), which consists of five main branches: temporal, zygomatic, buccal, marginal mandibular, and cervical. At the stylomastoid foramen in the skull, the facial nerve emerges, and the temporal branch of it crosses over the zygomatic arch, passing through the areolar tissue that makes up the surface of the temporal fascia, and subsequently enters into the frontalis muscle to provide deep innervation to the muscle.
The temporal nerve has three branches, the anterior, middle, and posterior, which are responsible for innervating the orbicularis oculi, frontalis, and corrugator muscles. The temporal (or frontal) branch of the facial nerve lies within the superficial layer of the temporoparietal fascia along with the temporal artery that runs just anterior to the nerve.
The temporal branch enters the deeper part of the frontalis muscle from the temporal branch. By cutting subcutaneously or just anterior to the superficial part of the deep temporal fascia (the glistening layer just in front of the temporalis muscle), it is possible to avoid injuring the temporal branch of the facial nerve.
There are two supratrochlear and supraorbital nerves that run along the same arteries and, in order to reach the superficial skin, penetrate through the frontalis. They are branches of the ophthalmic division of the trigeminal nerve and do not directly innervate the muscle, but instead innervate a layer of skin overlying the muscle. As the name implies, the medial branches of the supraorbital nerve are superficial and the lateral branches are deep.
Frontalis Muscle: Surgical Considerations
Understanding the anatomy of the frontalis is essential for reconstructive and cosmetic procedures. If a child is born with an absent or dysfunctional levator palpebrae superioris, as in bilateral congenital ptosis, the ptosis may be so severe that it causes vision obstruction and amblyopia.
Frontalis-orbicularis muscle advancement is possible in those patients. First described more than 100 years ago, the procedure involves making an incision at the crease of the upper eyelid, followed by vertical incisions into the frontalis muscle.
Finally, the muscle flap is advanced inferiorly to connect with the orbicularis oculi muscle. Ptosis correction using the frontalis is also known as frontalis slings or frontalis suspensions. This procedure is often preferred to muscle flap advancements and involves a similar approach, except it uses a suture to connect the frontalis to the tarsal plate.
This provides the necessary pull to elevate the eyelid with frontalis contraction, similar to the flap. Ptosis can result from mechanical, neurological, traumatic, or muscular dysfunctions, all of which can be treated by surgery.
Frontalis Muscle: Clinical Significance
Improved forehead skin:
In order to maintain a youthful appearance, people often seek to rejuvenate the forehead. As we age, relaxed skin tension lines, also known as wrinkles, appear perpendicular to the underlying muscles. In order to reduce lines, vascular changes, and skin pigment changes, non-surgical treatments are often the first step taken. There are nonsurgical options such as creams, peels, abrasives, and lasers.
Use of botulinum toxin for forehead and frown lines:
In minimally invasive procedures like botulinum injections, anatomy plays an important role. Botulinum toxin is effective for treating rhytides and wrinkles and can be injected directly into the frontalis muscle. The decreased muscular contraction leads to a decrease in rhytid production and a more youthful appearance.
Multiple injections into the frontalis are involved in this procedure. It is important to avoid complete paralysis of the frontalis muscle: 10 to 20 units of botox distributed across the forehead produces a satisfactory relaxation of the horizontal rhytids. As well as the frontalis, the corrugator and procerus muscles should also be injected.
2 cm above the brow is the safe zone for injections into the frontalis muscle. Experiencing the toxin in an improper manner can lead to nonpermanent ptosis of the levator palpebrae superioris. Maintaining a balance between the levators and depressors of the brow is also crucial.
When the frontalis muscle is weak and the depressors are dominant, the brow will descend. Additionally, improper distribution of botulinum into the medial frontalis can cause a “Spock” deformity, in which the lateral portion of the frontalis is capable of contraction, while the medial portion is relaxed.
One area of frontalis action that often goes untreated, especially in women, is where the frontalis closes to the anterior hairline, where prominent residual high horizontal rhytids result.
Fillers for grooves at the glabella:
Often, fillers are placed into the forehead to enhance the volume and fullness of the horizontal lines at the root of the nose (caused by the procerus muscle) as well as the verticle “elevenses” at the medial end of each brow, caused by the corrugator muscles.
A thorough understanding of the underlying anatomy, including the depth and location of the various muscles, is essential for avoiding devastating complications. Too much filler or a misplaced filler in the glabella (the area between the eyebrows and above the nose) can obstruct the retinal arteries and cause blindness. A wrong injection into an artery may cause blindness.
Supratrochlear, for example, could result in acute necrosis of the tissue. Injections of fillers are never forced or bolused. In addition, we have found that injecting small amounts of filler gently into the skin upwards is a safe method of treating wrinkles.
Upper and lower motor neuron facial palsy:
When evaluating a patient with a stroke, it is also critical to understand the nerve supply to the forehead. Strokes of the middle cerebral artery can cause contralateral facial paralysis, but these strokes rarely affect the forehead. Because the lower motor neurons responsible for innervating the top half of the face receive input from both hemispheres, but not the lower half. In the case of Bell palsy, we see full hemifacial paralysis when the lower motor neuron is injured.
Tissue expansion:
When repairing large forehead or nasal defects, tissue expansion is required. In the neck, the expanders are placed in front of the platysma, but in the forehead, it is crucial to place the expanders underneath the frontalis muscles, with incisions made in the hairline.
Other Issues
- The frontalis muscle is actually part of the occipitofrontalis muscle, which is two muscle bellies connected with the galea aponeurotic.
- Cavernous sinuses receive part of the venous drainage from the forehead.
- The frontalis muscle elevates the eyebrows, whereas the corrugator supercilii, orbicularis oculi, and procerus play a role in its depression.
- In middle cerebral artery strokes, the function of the forehead is often spared.
- In order to avoid injury to the sensory and motor nerves of the frontalis muscle, dissection planes should be subcutaneous, subperiosteal, or subgaleal.
- The medial branches of the supraorbital nerve are superficial, while the lateral branches are deep.
- Variations in the horizontal extent of the frontalis muscle must be considered, as these variations may affect the extent of brow ptosis.
- An appreciation of the surface and applied anatomy of the forehead and the extent of the frontalis muscle is necessary when performing surgery in this region or injecting toxins into it.
FAQs
What is the function of the frontalis muscle?
It is the frontalis muscle that elevates the eyebrows, while the corrugator supercilii, orbicularis oculi, and procerus play a role in its depression. When a stroke occurs in the middle cerebral artery, the forehead is often spared.
Where is the frontalis muscle and what does it do?
The frontalis muscles are the vertically oriented muscles in the forehead that lift the eyebrows. By contracting the forehead muscle, one elevates the eyebrows and concurrently develops horizontal forehead wrinkles.
How do I relax my frontalis muscle?
Relax your frontalis muscle by sitting comfortably and lowering your eyebrows as much as possible while frowning. Hold this position for five seconds, then raise your eyebrows as high as possible while smiling. Hold this position for five seconds then repeat the entire exercise ten times.
What is Frontalis attached to?
Since the frontalis muscle attaches to the skin around the eyebrows, its main function is to raise the eyebrows, causing the skin of the forehead to wrinkle.
What kinds of facial expressions are made possible by the frontalis muscle?
Frontalis muscle – lifts the eyebrows, makes horizontal forehead wrinkles when we are surprised. Orbicularis oculi – the circular muscle of the eye (consists of two muscles). Closes the eyelids, and squints the eye.