Occipitofrontalis

Musculus occipitofrontalis

Also known as: epicranius, frontalis, occipitalis, epicranial aponeurosis, galea aponeurotica

A scalp muscle with frontal and occipital bellies joined by the epicranial aponeurosis (galea). It raises the eyebrows and wrinkles the forehead.

Overview

The frontal belly has no bony attachment. It arises from the epicranial aponeurosis and inserts into the skin and superficial fascia of the eyebrows, where it blends with orbicularis oculi and procerus. The occipital belly arises from the lateral two-thirds of the superior nuchal line and the mastoid process and inserts into the aponeurosis. The tough epicranial aponeurosis (galea aponeurotica) is the third layer of the scalp (Skin, Connective tissue, Aponeurosis, Loose areolar tissue, Pericranium). The frontal and occipital bellies working alternately can move the scalp back and forth.

Frontalis raises the eyebrows, producing an expression of surprise or attention, and creates the horizontal forehead creases. It is the only elevator of the eyebrow and helps to raise the upper eyelid indirectly. People with ptosis often overuse it.

Location

Forehead and back of the scalp, over the frontal and occipital bones.

Parts & subdivisions

Frontal belly (frontalis)

From the galea to the skin of the eyebrows. Supplied by the temporal branch of CN VII.

Occipital belly (occipitalis)

From the superior nuchal line and mastoid to the galea. Supplied by the posterior auricular branch of CN VII.

Epicranial aponeurosis

The intermediate tendon of the muscle and layer 3 of the scalp.

Anatomy

Origin

Frontal belly: epicranial aponeurosis. Occipital belly: lateral two-thirds of the superior nuchal line of the occipital bone and the mastoid part of the temporal bone.

Insertion

Frontal belly: skin and superficial fascia of the eyebrows and forehead. Occipital belly: epicranial aponeurosis.

Action

Elevates the eyebrows and wrinkles the forehead (frontal belly); retracts the scalp (occipital belly).

Innervation

Facial nerve (CN VII): temporal branch (frontal belly) and posterior auricular nerve (occipital belly).

Nerve roots

Cranial nerve VII; no spinal roots

Arterial supply

Supraorbital and supratrochlear arteries (ophthalmic artery), superficial temporal artery, and occipital and posterior auricular arteries (external carotid).

Relations

Deep to it lies the loose areolar tissue layer, the "danger space" of the scalp, where infection can spread to the dural venous sinuses through emissary veins.

Clinical significance

Scalp wounds and the galea

Lacerations that cut through the galea gape because the frontal and occipital bellies pull the edges apart, and they bleed profusely because the vessels are held open by dense connective tissue. The galea must be sutured to stop the bleeding and close the wound.

Facial palsy test

Inability to raise the eyebrow on one side indicates an LMN (peripheral) facial nerve lesion. The forehead is spared in UMN lesions.