Occipitofrontalis muscle

Origin and insertion

Occipitofrontalis muscle consists of two muscle bellies connected by epicranial aponeurosis that spans the dome of the skull.

• Frontal belly overlies the forehead and has no bony attachments. Its superficial fibers originate from the dermis of the skin and subcutaneous tissue of the eyebrows, while deeper fibers arise from the superior parts of procerus, orbicularis oculi and corrugator supercilii muscles. The belly then courses posterolaterally to insert into the epicranial aponeurosis anteriorly to the coronal suture of the skull.
• Occipital belly overlies the back of the skull. It originates from the lateral two-thirds of the superior nuchal lines of occipital bone. After a short course superiorly, their muscle fibers insert into the epicranial aponeurosis posteriorly to the lambdoid suture.

Relations

Occipitofrontalis is found deep to the subcutaneous tissue of the skin of the scalp and superficial to the periosteum of the skull.

Once they leave the orbits, supraorbital and supratrochlear arteries and nerves travel over the anterior surface of the frontal belly. The anterior surface of the occipital belly is crossed by the greater occipital nerve and occipital artery.

Innervation

Both parts of the muscle are supplied by the facial nerve (CN VII) that gives off temporal branches for the frontal belly, and the posterior auricular nerve for the occipital belly.

Blood supply

Blood supply to both parts of occipitofrontalis comes from several branches;

• Frontal belly is supplied by the ophthalmic artery and frontal branch of superficial temporal artery
• Occipital belly receives blood from the occipital branch of posterior auricular and descending branch of occipital artery

All the arteries supplying this muscle are the branches of external carotid artery, except for the ophthalmic artery which arises from the internal carotid artery.

Function

Occipitofrontalis muscle has several actions depending on which of its attachments is fixed;

When its aponeurotic attachment is fixed, the frontal belly elevates the eyebrows and skin of the forehead, producing a facial expression of shock or surprise. When its forehead attachment is fixed, the frontal belly aids the procerus, orbicularis oculi and corrugator supercilii muscles to frown the eyebrows by pulling the skalp forwards and wrinkling the forehead. Since the muscle heads of the frontal belly are separated, it is possible to perform these movements on only one of the halves of the face.

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Occipital belly retracts the scalp when its nuchal part is fixed and moves it forwards when the aponeurotic attachment is fixed. These movements are insignificant on their own, but in case they occur simultaneously with contractions of the frontal belly, they help moving the entire scalp backwards and forwards respectively.

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