Our scalp is divided into 5 layers. Each layer can be easily remembered using the mnemonic SCALP:
- S = The skin on the head where hair grows. It contains the sebaceous glands and hair follicles.
- C = The connective tissue, a dense subcutaneous layer of fat and fibrous tissue that is found underneath the skin. This is where the nerves and blood vessels of the scalp are.
- A = The aponeurosis, also called epicranial aponeurosis, is the third layer. This is a tough layer of dense fibrous tissue that runs from the frontalis muscle located at the front of the scalp to the occipitalis located at the back of the scalp.
- L = The loose areolar connective tissue layer provides a level of separation between the upper 3 layers and the pericranium. It also provides an area of entry during craniofacial surgery and neurosurgery. It is sometimes also referred to as the “danger zone” because of how easy it is for infectious agents to spread through it and on to emissary veins, which can then drain into the cranium. The loose areolar tissue is made up of random bundles of collagen type 1 and collagen type 3. It is also rich in glycosaminoglycans and will be made up of more matrix than fibres. This layer also allows the more superficial layers of the scalp to be able to shift in relation to the pericranium.
- P = The pericranium is the dense layer of vascular connective tissue of the skull bones. It provides nutrients to the bones and the capacity for cellular repair. It can also be lifted from the bone to allow the creation of bone windows, like what is used in craniotomy.