Scalp Layers
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Direct answer
The scalp has five layers, remembered by the word SCALA: skin, dense connective tissue, aponeurosis (the galea linking frontalis and occipitalis), loose areolar tissue and pericranium. The first three are firmly bound together and move as one unit over the pericranium. The fourth, the loose areolar layer, is the dangerous layer, because infection in it spreads widely and can pass through emissary veins into the dural venous sinuses.
What you must remember
- Layers: thick hair-bearing skin with sebaceous glands; dense fibrofatty connective tissue anchoring skin to galea; the galea aponeurotica with frontalis and occipitalis forming occipitofrontalis; loose areolar tissue; and the pericranium over the skull bones.
- Dangerous layer: its emissary veins connect scalp veins with the dural venous sinuses, so sepsis can spread into the skull; blood also tracks forward in it to cause periorbital bruising after forehead injury.
- Blood supply: from the external carotid — superficial temporal, posterior auricular and occipital arteries — and from the ophthalmic artery — the supraorbital and supratrochlear arteries; rich anastomoses make wounds bleed profusely yet heal quickly.
- Sensory supply: in front, supraorbital and supratrochlear (V1) and zygomaticotemporal (V2); over the temple, auriculotemporal (V3); behind, greater occipital (posterior ramus of C2) and lesser occipital (C2, C3 of the cervical plexus).
- Motor supply: the facial nerve — temporal branches to frontalis and the posterior auricular branch to occipitalis.
- Suture attachment: the pericranium is firmly adherent at cranial sutures, limiting subperiosteal collections to a single bone.
- Clinical importance: caput succedaneum is subcutaneous birth oedema crossing sutures, while a cephalhaematoma is subperiosteal and confined to one bone; gaping wounds mean the galea is divided and must be stitched.
Common confusion
Separate the two birth swellings by layer: caput succedaneum lies in the skin and subcutaneous tissue and crosses suture lines, whereas cephalhaematoma lies under the pericranium and never crosses a suture. The vessels and nerves run in the dense second layer — which is why even superficial lacerations bleed heavily — not in the loose fourth layer.
Exam-focused takeaway
For theory, draw the five layers in section, mark where vessels, nerves and collections lie, and chart the nerve fields from trigeminal, cervical and facial sources. In viva, expect SCALA, the dangerous layer with emissary veins, and caput versus cephalhaematoma. For spotters, demonstrate the galea on a dissection and name the nerve supplying each scalp zone.
Frequently asked questions
What are the five layers of the scalp?
Skin, dense connective tissue, aponeurosis (galea), loose areolar tissue and pericranium — SCALA; the first three move together.
Why is the loose areolar layer dangerous?
Its emissary veins connect scalp veins with the dural venous sinuses, allowing infection to reach the cranial cavity.
What is the arterial supply?
Superficial temporal, posterior auricular and occipital arteries from the external carotid, and supraorbital and supratrochlear arteries from the ophthalmic artery.
How is the scalp supplied by nerves?
Sensory — supraorbital and supratrochlear (V1), zygomaticotemporal (V2), auriculotemporal (V3), lesser occipital (C2, C3) and greater occipital (C2); motor — facial nerve.
Differentiate caput succedaneum and cephalhaematoma.
Caput is subcutaneous birth oedema crossing sutures; cephalhaematoma is subperiosteal bleeding confined to one bone.
Why do scalp wounds bleed so profusely?
The dense connective tissue holds the anastomosing vessels open when divided, so they cannot retract and spasm as elsewhere.