Scalp

The scalp is the specialized area of the head where hair grows. It is part of a larger collection of structures known as the epicranium. This group of tissues covers the cranium, which is the skull. Anatomically, the scalp is bordered by the face at the front. It meets the neck at the sides and the back. The scientific study of the scalp and hair is called trichology. Understanding this area is vital for medicine and surgery.

The scalp is organized into five distinct layers. You can remember these using the mnemonic SCALP. The first layer is the skin, which contains hair follicles and sebaceous glands. These glands produce oils. The second layer is connective tissue. This is a dense subcutaneous layer of fat and fibrous tissue. It houses the nerves and blood vessels of the scalp. The third layer is the aponeurosis, also called the galea aponeurotica. This is a tough, fibrous tissue that anchors the upper layers in place. It runs from the frontalis muscle to the occipitalis muscle.

The fourth layer is the loose areolar connective tissue. This layer has a gel-like consistency. It is made of more matrix than fibers and is rich in glycosaminoglycans, or GAGs. This structure allows the superficial layers to shift over the pericranium. Surgeons often use this layer as an easy plane of separation during neurosurgery. However, it is also called the "danger zone." This is because infectious agents can spread through it via emissary veins. These veins drain directly into the cranium. The fifth and final layer is the pericranium. This is the periosteum of the skull bones. It is a membrane that provides nutrition to the bone and allows for repair.

Blood supply to the scalp is very efficient. It is provided by five pairs of arteries. Two pairs come from the internal carotid artery. These include the supratrochlear artery and the supraorbital artery. The supratrochlear artery supplies the midline forehead. The supraorbital artery supplies the lateral forehead and the vertex. The other three pairs come from the external carotid artery. These are the superficial temporal, occipital, and posterior auricular arteries. Because blood vessel walls are firmly attached to fibrous tissue, they do not retract easily. This means even a small wound can bleed profusely.

Nerves provide sensation and movement to the scalp. Sensory innervation includes several nerves. You can remember them using the mnemonic Z-GLASS. This stands for the Zygomaticotemporal, Greater occipital, Lesser occipital, Auriculotemporal, Supratrochlear, and Supraorbital nerves. These nerves allow you to feel touch and temperature. Motor innervation controls the muscles of the scalp. The occipitofrontalis muscle is split into two parts. The frontal belly, or frontalis muscle, is supplied by the temporal branch of the facial nerve. The occipital belly, or occipitalis, is supplied by the posterior auricular branch of the facial nerve.

Many medical conditions can affect the scalp. Common issues include dandruff, which is the shedding of dead skin cells. There are also infestations like head lice. Some people experience seborrhoeic dermatitis, which causes red, itchy, and flaky skin. In newborns, this condition is called cradle cap. More serious issues include tumors like basal-cell carcinoma or squamous cell carcinoma. Doctors may also perform hair transplants to treat hair loss. One common method is micro grafting. This involves using a knife with multiple blades to remove tissue from donor areas. This technique aims to produce naturalistic results by using the patient's existing hair.

The scalp is also significant in culture and aesthetics. For example, androgenic alopecia is a common cause of hair loss in men. This can be treated with medications like minoxidil. Aging can also change the appearance of the scalp. If the scalp becomes heavy and loose, it can cause the forehead to look low or lined. Surgeons can use a brow lift to address these changes. Historically, the term "scalping" refers to the act of removing a scalp as a trophy. This practice has occurred on multiple continents throughout history.