A: The aponeurosis (or galea aponeurotica) is the next layer. It is a tough layer of dense fibrous tissue which runs from the frontalis muscle anteriorly to the occipitalis posteriorly
L: The loose areolar connective tissue layer provides an easy plane of separation between the upper three layers and the pericranium. In scalping the scalp is torn off through this layer. It also provides a plane of access in craniofacial surgery and neurosurgery. This layer is sometimes referred to as the "Danger Zone" because of the ease by which infectious agents can spread through it to emissary veins which then drain into the cranium. The loose areolar tissue in this layer is made up of random collagen I bundles, collagen III and is highly vascular and cellular. It will also be rich in glycosaminoglycans (GAGs) and will be constituted of more matrix than fibers.
P: The pericranium is the periosteum of the skull bones and provides nutrition to the bone and the capacity for repair. It may be lifted from the bone to allow removal of bone windows (craniotomy).
The scalp plays an important role in the aesthetics of the face. Androgenic alopecia, or male pattern hair loss, is a common cause of concern to men. It may be treated by medication (eg finasteride) or hair transplantation with variable success. If the scalp is heavy and loose, a common change with aging, the forehead may be low, heave and deeply lined. The brow lift procedure aims to address these concerns.
The scalp is a common site for the development of tumours including: