Human Anatomy
Scalp
Scalp anatomy for MBBS: the five SCALP layers, dangerous area, emissary veins, arterial and nerve supply, mapped to NMC codes AN27.1 and AN27.2.
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Scalp
Scalp anatomy for MBBS: the five SCALP layers, dangerous area, emissary veins, arterial and nerve supply, mapped to NMC codes AN27.1 and AN27.2.
This chapter covers the scalp, its five named layers and their clinical importance. It explains why scalp wounds bleed heavily, how infection spreads in the dangerous loose layer through emissary veins, and the arterial and nerve supply that make the scalp behave the way it does.
High-yield: Scalp
- The scalp has five layers, remembered by the word SCALP: skin, connective tissue, aponeurosis, loose areolar tissue and pericranium.
- The first three layers are firmly bound together and move as a single unit over the loose fourth layer.
- The dense connective tissue layer holds the vessels open when cut, so scalp wounds bleed profusely.
- The aponeurotic layer is the epicranial aponeurosis connecting the frontal and occipital bellies of occipitofrontalis.
- Deep scalp wounds gape only when the aponeurosis is cut, because it is under tension from the two muscle bellies.
- The loose areolar layer is the dangerous area of the scalp because infection spreads easily within it.
- The loose layer has emissary veins that connect scalp veins to the intracranial venous sinuses.
- Infection in the loose layer can pass through emissary veins to cause meningitis or sinus thrombosis.
- The scalp is supplied by five arteries on each side: supratrochlear and supraorbital in front, and superficial temporal, posterior auricular and occipital behind.
- The supratrochlear and supraorbital arteries arise from the ophthalmic branch of the internal carotid artery.
- The other three scalp arteries are branches of the external carotid artery.
- Sensory supply in front comes from the trigeminal nerve and behind from cervical nerves.
- The rich anastomosis between scalp arteries means avulsed scalp flaps can survive on a narrow pedicle.
- Collections of blood in the loose areolar layer can track forward into the eyelids, giving a black eye.
The five layers of the scalp
- **Skin:** Thick, hairy, with many sebaceous glands, so a common site of sebaceous cysts.
- **Connective tissue:** Dense, richly vascular; holds severed vessels open so wounds bleed freely; carries nerves and arteries.
- **Aponeurosis:** Epicranial aponeurosis linking occipitofrontalis; when cut, the wound gapes.
- **Loose areolar tissue:** The dangerous layer; allows spread of infection and blood; contains emissary veins to the venous sinuses.
NMC competencies in this chapter
- **AN27.1:** Layers of the scalp and their attachments
- **AN27.2:** Blood supply, nerve supply and applied anatomy of the scalp
Frequently Asked Questions
Why do scalp wounds bleed so heavily?
The second layer, the dense connective tissue, is richly vascular and holds the walls of cut vessels open so they cannot retract and close. As a result scalp wounds bleed profusely even when small.
Why is the loose areolar layer called the dangerous area?
The loose fourth layer lets pus and blood spread widely, and its emissary veins connect to the intracranial venous sinuses. Infection here can therefore spread inside the skull and cause meningitis or sinus thrombosis.
What is the arterial supply of the scalp?
Each side is supplied by five arteries: the supratrochlear and supraorbital from the internal carotid system, and the superficial temporal, posterior auricular and occipital from the external carotid system.
Why can an avulsed scalp flap survive?
The scalp arteries anastomose freely with each other across the midline and between sides, so even a scalp flap left attached by a narrow pedicle can receive enough blood to survive and be reattached.
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