Skull and Scalp Anatomy

Skull and Scalp

• The skull is composed of two parts: the neurocranium (cranial vault) and the viscerocranium (facial bones).
• The neurocranium protects the brain.
• The viscerocranium forms the face.
• The neurocranium has 8 bones: ethmoid, sphenoid, frontal, occipital, and two parietal bones, two temporal bones.
• The viscerocranium has 14 bones: vomer, mandible, inferior conchae (2), nasal (2), lacrimal (2), maxilla (2), palatine (2), and zygomatic (2).
• The skull contains 22 bones in total (21 are immobile, 1 is mobile: the mandible).
• Skull bones are composed of external and internal tables (compact bone), diploë (spongy bone), and sutures.

Specific Learning Outcomes

• Bones: Identify and list the bones that construct the skull.
• Positions: Define the anatomical position of the skull.
• Landmarks: Identify bregma, lambda, pterion, and asterion, and describe their clinical significance.
• Comparison: Compare characteristics between adult and neonatal skulls.
• Layers: Describe the layers of the scalp and their clinical significance.
• Supplies: Detail the innervation and blood supply of the scalp.

Anatomical Position of the Skull

• The skull's anatomical position has the forehead facing forward, while the eyes and mouth should be forward-facing, as well as the nose pointing directly forward.

Skull Landmarks

• Bregma: The junction of the coronal and sagittal sutures.
• Lambda: The junction of the sagittal, and lambdoid sutures.
• Pterion: The junction of the frontal, parietal, temporal, and sphenoid bones. A significant landmark for the middle meningeal artery.
• Asterion: The junction of the parietal, occipital, and mastoid processes of the temporal bone.

Skull Bones (Anterior View)

• Frontal: Forehead bone.
• Nasal: Bridge of the nose.
• Maxilla: Upper jaw.
• Zygomatic: Cheekbone.
• Mandible: Lower jaw.

Skull Bones (Lateral View)

• Frontal: Forehead bone.
• Parietal: Top of the head.
• Temporal: Below the parietal bone, near the ear.
• Occipital: Back of the head.
• Zygomatic: Cheekbone.
• Maxilla: Upper jaw.
• Mandible: Lower jaw.

Skull Bones (Important Points, Lateral View)

• Pterion: A crucial, often weak point in the skull's lateral aspect, where multiple bones connect. This location sits over the middle meningeal artery.
• Nasion: Intersection of the frontal and nasal bone.
• Anterior Nasal Spine: An important landmark on the nasal bone.
• Sagittal suture: The suture between the two parietal bones.
• Lambdoid suture: A suture (junction) between the parietal bone and the occipital bone at the posterior aspect of the skull.
• Coronal suture: Suture between the frontal bone and the parietal bones.

Skull Foramens (Anterior View)

• Supraorbital notch/foramen
• Zygomaticotemporal foramen
• Zygomaticofacial foramen
• Infraorbital foramen
• Mental foramen

Skull Structures (Posterior View)

• Superior nuchal line: A prominent superior line on the occipital bone
• Inferior nuchal line: A curved line inferior to the superior nuchal line.
• External occipital protuberance: A bump at the junction of the nuchal lines.
• External occipital crest: A ridge extending from the external occipital protuberance.

Skull Structures (Posterior View)

• Occipital bone: At the back of the skull, houses the foramen magnum.
• Parietal bone: Top of the head
• Temporal bone: Near the ear
• Vomer: A facial bone

Neonatal Skull

• Bones are smooth and unilaminar (lack diploë).
• The neurocranium is relatively large compared to the face.
• This is due to rapid growth of the mandible, maxillae, and paranasal sinuses.

Fontanelles

• Are unossified membranous intervals (gaps in the skull).
• Anterior fontanelle: Diamond-shaped, fuses by 18-24 months.
• Posterior fontanelle: Triangular-shaped, fuses by 1 year.
• Sphenoidal/anterolateral: fuses by the age of 18-24 months
• Mastoid/posterolateral: fuses by the age of 18-24 months.

Layers of the Scalp

• Skin: The outermost layer, containing hair follicles.
• Connective tissue: Anchors skin to the next layer.
• Aponeurosis: Flat tendon-like tissue uniting frontal and occipital muscles.
• Loose areolar tissue: Connects scalp veins to the intracranial venous sinuses. Contains emissary veins. (Dangerous layer due to potential for infection spreading.)
• Periosteum: Outer covering of the skull bone

Scalp Innervation

• Anterior: Supratrochlear, supraorbital, zygomaticotemporal, and auriculotemporal nerves (from the trigeminal nerve).
• Posterior: Great auricular, lesser occipital, and great occipital nerves (cervical nerves).
• Also: Temporal branch of facial nerve

Scalp Blood Supply

• Anterior: Supratrochlear, supraorbital, and superficial temporal arteries.
• Posterior: Posterior auricular and occipital arteries.
• Also: ophthalmic branches from the internal carotid artery.