Layers of the Scalp - Mnemonic: SCALP

S - Skin

• The outermost layer, structurally similar to skin elsewhere on the body.
• Contains hair follicles, sebaceous glands, and sweat glands.
• Hair is present over most of its surface.

C - Connective Tissue (Dense)

• Deep to the skin; anchors the skin firmly to the layer below.
• Contains arteries, veins, and nerves supplying the scalp.
• Clinically important: when the scalp is cut, the dense connective tissue holds cut vessels open, preventing them from contracting - this causes profuse bleeding from even minor scalp wounds.

A - Aponeurotic Layer (Galea Aponeurotica / Epicranial Aponeurosis)

• The deepest of the top three "firmly attached" layers.
• Consists of the occipitofrontalis muscle - with a frontal belly anteriorly and an occipital belly posteriorly - connected by the epicranial aponeurosis (galea aponeurotica).
• The first three layers (S, C, A) are tightly bound together as a single unit, called the "scalp proper" - the part avulsed in traumatic scalping injuries.

L - Loose Connective Tissue

• Separates the aponeurotic layer from the pericranium.
• Allows the scalp proper to move freely over the skull (why you can wrinkle your forehead).
• Called the "danger zone" of the scalp: infections here spread easily through this plane and can track intracranially via emissary veins (valveless veins connecting extracranial to intracranial dural venous sinuses), potentially causing meningitis or cavernous sinus thrombosis.
• Hematomas in this layer ("subaponeurotic hematoma") spread widely across the scalp.

P - Pericranium

• The deepest layer; the periosteum of the outer surface of the calvaria.
• Firmly attached to skull bones but loosely attached at suture lines.
• Subperiosteal hematomas (cephalohematomas in neonates) are limited by suture lines because the pericranium is tightly adherent there.

Key Clinical Points

Gray's Anatomy for Students, Chapter 8 (Head)

Layers Below the Scalp (Superficial to Deep)

1. Skull (Calvaria) - 3 Sub-layers

The inner table fractures more easily than the outer table - this is why intracranial injury can occur even without obvious outer scalp damage.

2. Cranial Dura Mater - 2 Sub-layers

• Dural folds/partitions - falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae
• Dural venous sinuses - superior sagittal sinus, transverse sinus, etc.

3. Arachnoid Mater

• A thin, delicate, avascular membrane applied to the inner surface of the dura.
• Spider-web-like trabeculae extend from it down to the pia mater.
• No blood vessels in the arachnoid itself.
• Between arachnoid and pia = Subarachnoid space, filled with cerebrospinal fluid (CSF) and containing cerebral arteries and veins.

4. Pia Mater

• The innermost, most delicate meningeal layer.
• Closely adherent to the surface of the brain, following every gyrus and sulcus.
• Highly vascular - carries blood vessels that dip into the brain substance.
• Cannot be separated from the brain surface without causing damage.

5. Brain (Cerebral Cortex)

Complete Sequence: Scalp to Brain

SCALP:
  S - Skin
  C - Connective tissue (dense)
  A - Aponeurosis (galea)
  L - Loose areolar tissue  ← "danger zone"
  P - Pericranium (outer periosteum of skull)

SKULL:
  - Outer table
  - Diploe (with diploic veins)
  - Inner table

MENINGES:
  - Extradural space (potential)
  - Dura mater:  Periosteal layer + Meningeal layer
  - Subdural space (potential)
  - Arachnoid mater
  - Subarachnoid space (contains CSF)
  - Pia mater

BRAIN:
  - Cerebral cortex (grey matter)

Clinical Correlation: Haematomas at Each Level

Source: Gray's Anatomy for Students, Chapters 1 and 8