Scalp

The scalp is the skin and subcutaneous tissue covering the neurocranium. It is composed of five layers and has a rich vascular supply which explains why it bleeds profusely and heals well.

Layers

The scalp is composed of five layers which are easily remembered with this mnemonic. From external to internal the layers are:

1. skin
   • usually covered in hair
   • thicker over the occiput
   • rich arterial supply and venolymphatic drainage
2. connective tissue
   • ​thick layer which has a rich vascular supply
   • contains numerous cutaneous nerves
3. Galeal aponeurosis (also known as the Galea aponeurotica or epicranial aponeurosis)
   • strong aponeurosis that allows attachment for muscles of the scalp (occipitofrontalis, temporoparietalis and superior auricular muscles), all innervated by the facial nerve
4. loose areolar tissue:
   • a sponge-like layer of areolar tissue which allows the free movement of the first three layers over the underlying pericranium and skull
   • being so loose it is a potential space for collections and hematomas
5. pericranium:
   • dense layer of fibrous connective tissue that is the external periosteum of the neurocranium (firmly attached)
   • extends into the cranial sutures

Boundaries

• posterior: superior nuchal lines of the occipital bone
• anterior: supraorbital margins of the frontal bone
• lateral: zygomas

Blood supply

Numerous arteries supply the scalp with corresponding veins, contributing to  rich vascular supply. The arteries arise from both the internal and external carotid circulations:

• external carotid artery branches
  • superficial temporal artery
  • occipital artery
  • posterior auricular artery
• internal carotid artery branches
  • supraorbital artery
  • supratrochlear artery

Venous drainage via corresponding veins and via emissary veins to dural venous sinuses.

Lymphatic drainage

Like the face, the scalp does not have lymph nodes. Lymph drains via small lympatic channels to the submandibular, parotid, mastoid and occipital nodes. These form a collar of nodes at the junction of the head and neck.

Innervation

Numerous cutaneous nerves supply sensation to the scalp depend on the location:

• anterior scalp (branches of the ophthalmic division of the trigeminal nerve):
  • supratrochlear nerve
  • supraorbital nerve
  • lacrimal nerve
• superior scalp towards the vertex
  • supraorbital nerve
• posterior scalp
  • greater occipital nerve (from C2)
  • third occipital nerve (C3)
• lateral scalp (from anterior to posterior)
  • zygomaticotemporal nerve
  • zygomaticofacial nerve
  • Auriculotemporal nerve (branch of mandibular division of trigeminal nerve)
  • lesser occipital nerve (C2, C3 from the cervical plexus)

The muscles of the scalp (see above) are considered muscles of facial expression and therefore all innervated by the facial nerve.

Related pathology

• scalp hematoma