Scalp Anatomy: Layers of the Scalp

The Scalp

• The scalp has 5 layers, the first 3 are bound and move as a single unit.
• The acronym SCALP is derived from the first letter of each layer.

Layers of the Scalp

• Skin: The outer layer, thick, hairy, and contains sebaceous glands.
• Connective Tissue: Fibrofatty tissue beneath the skin with fibrous septa connecting to the occipitofrontalis muscle.
• Arteries and veins, branches of the external and internal carotid arteries, are in this layer and freely anastomose.
• Aponeurosis (Epicranial): A thin, tendinous sheet connecting the occipital and frontal bellies of the occipitofrontalis muscle.
• Margins attach to the temporal fascia.
• Loose Areolar Tissue: Occupies the subaponeurotic space and connects the epicranial aponeurosis to the pericranium.
• Contains small arteries and emissary veins that connect superficial scalp veins to the diploic veins of the skull and intracranial venous sinuses.
• Pericranium: Periosteum covering the outer surface of the skull bones.
• At sutures between skull bones, it merges with the periosteum on the inner surface.

Occipitofrontalis Muscle

• Origin, insertion, nerve supply, and action can be found in a table.

Occipitofrontalis Muscle Actions

• When the muscle contracts, the first three layers of the scalp move forward or backward.
• Loose areolar tissue allows the aponeurosis to move on the pericranium.
• Frontal bellies can raise eyebrows in surprise or horror.

Sensory Nerve Supply

• Main sensory nerve trunks are located in the superficial fascia.
• Supratrochlear Nerve: Branch of the ophthalmic trigeminal division.
• Winds around the superior orbital margin to supply the scalp and reaches the vertex of the skull.
• Supraorbital Nerve: Branch of the ophthalmic trigeminal division.
• Winds around the superior orbital margin and ascends over the forehead, supplying the scalp as far back as the vertex.
• Zygomaticotemporal Nerve: Branch of the maxillary trigeminal division.
• Supplies the scalp over the temple.
• Auriculotemporal Nerve: Branch of the mandibular trigeminal division.
• Ascends over the side of the head from in front of the auricle, has terminal branches supply the skin over the temporal region.
• Lesser Occipital Nerve: Branch of the cervical plexus (C2).
• Supplies the scalp over the lateral part of the occipital region and the skin over the medial surface of the auricle.
• Greater Occipital Nerve: Branch of the posterior ramus of the 2nd cervical nerve (C2).
• Ascends over the back of the scalp and supplies the skin as far forward as the vertex of the skull.

Arterial Supply

• The scalp has high blood supply nourish hair follicles, cuts bleed heavily because of arteries located in the superficial fascia
• The supratrochlear and supraorbital arteries are branches of the ophthalmic artery, ascending over the forehead together.
• Superficial Temporal Artery: Branch of the external carotid artery, ascends in front of the auricle with the auriculotemporal nerve.
• Divides into anterior and posterior, supplying the skin over the frontal and temporal.
• Posterior Auricular Artery: Branch of the external carotid artery, ascends behind the auricle, supplies the scalp above and behind it.
• Occipital Artery: Branch of the external carotid artery, ascends with the greater occipital nerve.
• Supplies the skin over the back of the scalp, reaching as high as the vertex of the skull.

Venous Drainage of the Scalp

• Supratrochlear and Supraorbital Veins: unite on the medial margin of the orbit to form the facial vein.
• Superficial Temporal Vein: in the parotid gland unites with the maxillary vein to become the retromandibular vein..
• Posterior Auricular Vein: below the parotid gland unites with the retromandibular posterior division to form the external jugular vein.
• Occipital Vein: to suboccipital venous plexus which flows into the vertebral or internal jugular veins.

Lymph Drainage of the Scalp

• Anterior scalp and forehead lymph vessels drain into the submandibular nodes.
• Lateral scalp above the ear drains into the superficial parotid (preauricular) nodes.
• Scalp above and behind the ear drains into the mastoid nodes.
• Back of the scalp drains into the occipital nodes.

Clinical Notes

• Skin of the scalp has many sebaceous glands prone to infection and damage from combs.
• This causes scalp sebaceous cysts to be common.
• Small scalp cuts can cause severe blood loss because arterial walls attach to fibrous septa so vessels can't contract.
• Local pressure is used to stop the bleeding.
• Scalp infections are typically localized and painful due to abundant fibrous tissue.
• Scalp infections can spread through emissary veins to the skull bones causing osteomyelitis.
• Infected blood in the diploic veins may travel via emissary veins further to produce venous sinus thrombosis,.
• Blood or pus can collect in the potential space beneath the epicranial aponeurosis leading to spread over the skull.