SCALP

The scalp is the region of the head that extends from the forehead to the back of the neck and covers the skull. It consists of five layers that together form a continuous, hair-bearing shield: skin, subcutaneous tissue, the galea aponeurotica, loose areolar tissue, and pericranium.

The five-layer structure is commonly remembered by the acronym S.C.A.L.P. The skin contains hair follicles, sebaceous glands, and sweat glands. The subcutaneous tissue is rich in blood vessels and nerves. The galea aponeurotica is a strong fibrous layer that connects the frontalis and occipitalis muscles. Beneath it lies loose areolar tissue, a potential space that permits movement of the scalp over the skull. The pericranium is the periosteum of the skull.

Blood supply to the scalp comes mainly from branches of the external carotid artery, including the superficial temporal, posterior auricular, and occipital arteries; venous drainage mirrors these patterns. Sensory innervation is provided primarily by branches of the trigeminal nerve (notably V1 and V2) and by the greater occipital nerve.

Functions of the scalp include protecting the skull, housing hair and sebaceous glands, and contributing to thermoregulation. Its rich vascular supply aids rapid healing after injuries. Clinically, the scalp is susceptible to dermatitis and other inflammatory conditions, infections, and hair loss disorders. Scalp injuries can bleed profusely due to vascularity; the loose areolar layer can permit rapid spread of infection or fluid, and infections may extend through emissary veins to intracranial structures. In surgery, the layered anatomy of the scalp informs flap design and wound management.