This section describes the skull structures, scalp, and associated structures.

Scalp Layer, Muscles, Nerves, Arteries, Veins

Skin

Five layers

Skin - with associated hair follicles, sweat glands and sebaceous glands

Connective tissue - dense fibrous connective tissue surrounding arteries and nerves

Aponeurosis - thin tendinous sheet, tightly attached to skin and connective tissue above; moveable anteriorly and posteriorly, laterally attached to temporal fascia, attached to frontalis and occipitalis muscles

Loose areolar tissue - loosely connects epicranial aponeurosis to periosteum of skull; crossed by emissary veins

Pericranium - periosteum (connective tissue layer) of outer side of skull

Muscles of the Scalp and Face

• Epicranius (occipitofrontalis)
  • bipartite muscle consisting of the:
    • Frontalis
    • Occipitalis
    • Galea aponeurotica – cranial aponeurosis connecting above muscles
• These two muscles have alternate actions of pulling the scalp forward and backward

Muscles of the Face

Internal Structure of Calvarium (skull cap)

The calvarium is the skull that overlies the convexity of the brain.

• Consists of hard inner and outer tables of cortical bone surrounding layer of spongy bone (diploe)

• Diploic veins – course within diploe, connects cranial cavity and surface of skull

Innervation

• Branches of Trigeminal nerve:

  • Supratrochlear and Supraorbital nerves (anterior scalp)

  • Zygomaticotemporal and Auriculotemporal nerves (lateral scalp)

• Cervical spinal nerves:

  • Lesser Occipital nerves (from ventral ramus of C2)

  • Greater Occipital nerves (from dorsal ramus of C2) innervate lateral and posterior scalp

Blood Supply to Calvarium

• Outer surface receives branches from arteries to scalp

• Inner surface receives branches from meningeal arteries (coursing immediately below bone)

Arterial Supply

• Branches of Ophthalmic artery: Supratrochlear and Supraorbital arteries (anterior scalp)

• Branches of External Carotid artery

  • superficial Temporal artery (to lateral scalp)

  • Posterior auricular artery (scalp above and posterior to external ear)

  • Occipital artery (posterior scalp)

• Extensive anastomoses between arteries and scalp can cause profuse bleeding

Veins of Scalp

See above diagram also

Veinous Drainage

• By veins with same names as arteries; also drain via emissary veins (passing into diploe) into interior of skull

Emissary Veins

• connect intracranial venous system with extracranial (face & scalp) veins
• blood flow can be in either direction as there are no valves
• therefore potential for infection to spread from face or scalp to brain!

Neuraxial Skeleton

Human skeleton consists of two main divisions

• Axial skeleton – bones that form upright axis of the body, skull, hyoid, vertebral column, sternum, and ribs
• Appendicular skeleton – bones that are appended to axial skeleton, upper and lower extremities

SKULL

• Bony parts
  • cranium [upper part]
  • base of skull [lower part of cranium]
  • face - is below and attatched to base
• Aspects
  • anterior
  • lateral
  • posterior
  • inferior
• Sutures
  • join the flat bones of the skull and allow for growth of the cranium
• Internal surface
  • anterior, middle and posterior cranial fossae
• Postnatal growth and development
  • intramembranous and enchondral ossification
• Functions:
  • Protects brain
  • Supports organs of special senses
  • Provides foundation for structures that take air, food , water into body

SKULL

• Rounded area that houses and protects the brain
• Comprised of 8 distinct bones that are fused together in the adult
  • 1-frontal bone
  • 2-parietal bones
  • 2-temporal bones
  • 1-sphenoid bone
  • 1-ethmoid bone
  • 1- occipital bone

Cranial Cavity

Anterior cranial fossa

frontal bone, frontal lobes, cribriform plate and crista galli of ethmoid bone, falx cerebri, lesser wing of sphenoid b.

Middle cranial fossa

temporal bone. greater wing of sphenoid, temporal lobes,optic canal, foramen rotundum, foramen ovale, foramen spinosum, sup. orbital fissure, foramen lacerum and carotid canal, sella turcica and hypophysis.

Posterior cranial fossa

squamous occipital and petrous temporal bones, cerebellum, pons and medulla, tentorium cerebelli, foramen magnum, jugular foramen, internal auditory canal,hypoglossal canal #13;

Frontal Bone

• Forms the forehead and the anterior part of the cranial floor

• Contains 2 mucosa-lined, air-filled spaces known as the frontal sinuses, these form the upper orbits of the eyes

• Unites with the 2 parietal bones posteriorly in an immovable joint – the coronal suture

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Frontal Bone Markings

• Supraorbital margin – arched ridge just below eyebrow

• Frontal sinuses – cavities inside bone just above the supraorbital margin

• Bregma – midpoint of coronal suture

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Anterior View of Bony Landmarks on the Face

The Parietal Bones

• 2 bones that form largest portion of the top and sides of the cranium
• Prominent, bulging bones behind the frontal bone
• Fused down the middle at the top of the skull

Parietal Bone Sutures

• Form immovable joint with several bones:
  • Lambdoidal suture with the occipital bone
    • Lambda – midpoint of lambdoidal sutures
  • Squamous suture with the temporal bones and part of the sphenoid bone
  • Coronal suture with the frontal bone
  • Sagittal suture between parietal bone

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• 2 distinct bones that form lower, central sides and part of the floor of the skull

• Houses the middle and inner ear structures and contains the mastoid sinuses

• Mastoiditis – an inflammation of the mucosa lining of these spaces

Temporal Bone Markings

• Squamous portion – thin, flaring upper part of bone

• Petrous portion – wedge-shaped process that forms part of center section of cranial floor between sphenoid and occipital bones.Name derived from Greek word meaning stone due to extreme hardness of this process

• Mastoid portion – rough-surfaced lower part of bone posterior to external auditory meatus

• Irregular, delicate, spongy bone located between the eyes

• Forms anterior part of frontal floor, medial walls of the orbits, sidewalls of the nasal cavity and part of nasal roof (cribriform plate)

• Ethmoid sinuses – within lateral masses of ethmoid bone are honeycombed, mucosa- lined, air spaces

Ethmoid Bone Markings

• Horizontal (Cribriform) plate – perforated by small foramina where olfactory nerves pass through to reach the brain

• Crista galli – meninges attach to the process

• Perpendicular plate – forms upper part of nasal septum

• Forms back base of skull
• Forms immovable joints with 3 other cranial bones:
  • the parietal,
  • temporal,
  • sphenoid
• Forms moveable joint with the first cervical vertebra

Occipital Bone Markings

• Foramen Magnum – hole through which spinal cord enters cranial cavity
• Condyles – convex, oval processes on either side of the foramen magnum, articulates with depressions on first cervical vertebra

• Occipital bone
• Lambdoid suture
• Sutural bones
• External occipital protuberance

  • Ligamentum nuchae : Helps keep head erect
  • Nuchal lines : Neck muscle attachment points

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  The Sphenoid Bone

  

• Keystone of cranial floor, forms its midportion
• Resembles a bat with wings outstretched and legs extended downward posteriorly
• Lies behind and slightly above nose and throat
• Forms part of floor and sidewalls of orbits.
• Contains fairly large, mucosa-lined, air-filled spaces within central part of sphenoid – sphenoid sinuses

  Sphenoid Bone Markings

• Body – hollow, cube-like central portion
• Greater wings – lateral projections from body, form part of outer wall of orbits
• Lesser wings – thin, triangular projection from upper part of sphenoid body
  • forms posterior part of roof of orbit.
• Sella turcica (or Turk's saddle) saddle-shaped depression on upper surface of sphenoid body, contains pituitary gland
• Optic foramen – opening into orbits at roof of lesser wing, transmits 2 nd cranial nerve
• Pterion – area of junction of Sphenoid, Temporal, Parietal, and Frontal bones

• In infants bones are further apart and joined by fontanelles
• Permit cranial compression at birth and cranial growth later
• Anterior fontanelle at Bregma
• Posterior fontanelle at Lambda
• Lateral fontanelle at Pterion

Basic Study Questions

1. Name the 5 layers of the scalp

2. Identify the major cranial bones and associated sutures

3. What area of the sphenoid bone contains the pituitary gland?

Additional Study Questions