Skull Lab anatomical concepts and development

Foramen

Round opening/hole/passage in bone

Fissure

nature division/narrow passage (slit-like) through bone

Fossa

bony depression or hollow space formed by various structures (including bone)

Meatus

tube-like channel extending within bone

Sulcus

crevice or groove in bone (typically due to adjacent blood vessels, nerves, etc.)

Sinus

air-filled bony cavity (lined with mucous membrane)

Crest/Line/Ridge

raised and/or prominent bony processes

Name of skill division marked

Neurocranium (braincase, cranial vault)

Function of Neurocranium

Protection of brain

Name of skill division marked

Visceral cranium (facial skeleton)

Function of the visceral cranium

- gives a characteristic shape to the human face
- protection of delicate organs of the face
- provides a bony surface for attachment of facial muscles
- contains many foramina for the passage of neuro structures

what bones make up the neurocranium?

- 1 Frontal bone
- 1 Ethmoid bone
- 1 Sphenoid bone
- 1 Occipital bone
- 2 Temporal Bones
- 2 Parietal Bones

What bones make up the Visceral Cranium?

1 mandible, 1 vomer, 2 maxillae, 2 palatine, 2 zygomatic, 2 nasal, 2 lacrimal, 2 inferior conchae

What features of the neurocranium allow it to protect the brain?

- layered composition of bones allows a force to radiate over a larger surface area
- Joints at articulations are immoveable (i.e. sutures)
- Inernal bone structures are trianfulated to support the contents of the neurocranium (i.e. buttress of the skull)

~ protection of the brain is also facilitated by meninges~

What are the Layers of bone in skull?

1. Outer table: compact bone
2. Diploe: Spongy bone
3. Inner table: compact bone

what are cranial sutures? what are they made up of?

immoveable joints, made up of fibrous connective tissue

do sutures contain diploe?

no, this makes the skull thinner and more susceptible to injury in these areas

Structure of the Skull

Triangulated to support contents of neurocranium
Formed by lesser wings of sphenoid bone and petrous portion of the temporal bones

What are the meninges?
what is the meninges function?

membranous layers of connective tissue that cover the brain (and spinal cord)
(in between the skull and brain)

- protect the brain and spinal cord from mechanical
- provide a framework for vasculature

what are the three meninges layers?
what are the spaces associated with these layers?
(all in order! from external to internal)

~ Epi-dural space (potential space)
1. Dura Mater
~ Sub-dural Space (potential space)
2. Arachnoid Mater
~ Sub-arachnoid space (real space)
3. Pia Mater

Describe the Dura Mater
- what is it made of?

- outer periosteal layer and inner meningeal layer
- thick, fibrous, strong (DICT)
- Vascular

Describe the Arachnoid Mater
- What is it made of?

- thin (LCT)
- Avascular

what is in the sub-arachnoid space, where is it

located in between the arachnoid mater and pia mater

contains Cerebral Spinal Fluid

Describe the Pia Mater

Tightly adhered to brain and spinal cord
very thin
vascular

Dura Mater

Sub-dural Space

Arachnoid Mater

Sub-Arachnoid Space

Pia Mater

What are the Dural folds?

Membranes that divide the cranial cavity into compartments and support the brain and spinal cord
-- 2 large folds: Falx Cerebri and Tentorium Cerebelli
-- 2 small folds: Falx Cerebelli and Diaphragma Sellae

Falx Cerebri

Falx Cerebelli

diaphragma sellae

tentorium cerebelli

How are most bones of the skull formed?

intramembranous ossification
direct conversion of mesenchymal cells -> Bone (no cartilage precursure)
- only capable of appositional growth

Fontanelles and its purpose

A soft membranous gap between of hyaline cartilage between the cranial bones of the calveria in the fetus and infant (also called "soft spots")
- allows movement and molding of head through birth canal during labor
- allows more rapid post-natal growth of brain

when does osteogenesis begin?

6-7 weeks gestation

When do the tables and diploe develop?

by the 4th year of life

What are the fontanelles

- Anterior (F1)
- Posterior (F2)
- Sphenoidal or anterolateral (F3) [paired]
- Mastoid or posterolateral (F4) [paired]

When does each Fontanelle close?

- Anterior (F1): closes 18-24 months last to close!

- Posterior (F2): closes 2-3 Months first to close!

- Sphenoidal or anterolateral (F3) [paired]: closes at 2-3 months

- Mastoid or posterolateral (F4) [paired]: closes by 12 months

What is an F1 suture in an infant called?

interfrontal suture

What is the F1 suture in adults?
what can it increase risk of?

Mesopic suture
can increase risk of fracture in that area

Views of the skull:

• Norma verticalis

• Norma dorsalis (occipitalis)

• Norma lateralis

• Norma frontalis

• Norma basalis

• Inside of skull

Structures seen from Norma verticalis

Bones visible: Frontal, 2 parietal, and occipital bone

Sutures: coronal, sagittal, lambdoid

Foramen: 2 parietal foramen

Craniometric points visible: bregma, lambda, and vertex (highest point, no sutures)

Structures seen from Norma Dorsalis (occipitalis)

Bones visible: 2 parietal bones, occipital bone, 2 temporal bones

Sutures: Sagittal, lambdoid, parietomastoid, occipitomastoid

Foramen: 2 parietal foramen

Craniometric points visible: lambda, asterion

Other notable features seen from Norma Dorsalis (occipitalis)

• superior nuchal line (trapezius, splenic capitis, and occipitalis muscle attach here)

• inferior nuchal line (attachment site for 3 deep neck muscles)

• external occipital crest

• external occipital protuberance (marks junction of head and neck)

Bones visible from Norma Lateralis

• frontal bone

• 2 parietal bones

• 2 temporal bones

• occipital bone

• 2 zygomatic bones

• 2 maxillary bones

• mandible

• 2 nasal bones

• sphenoid

• ethmoid

• 2 lacrimal bones

What is the pterion

Area in the temple region where five sutures join.
Sutures contain no diploe (only inner and outer table) = thinnest and weakest portion of the skull.

The 5 sutures that form the Pterion

• coronal suture: joins frontal bone to sphenoid and parietal bones

• sphenosquamous suture: joins sphenoid and temporal bones

• squamous suture: joins temporal bone to sphenoid and parietal bones

• sphenoparietal suture: joins sphenoid and parietal bones

• sphenofrontal suture: joins sphenoid and frontal bones

Parietal bone attachment sites for what muscle and where?

attachment sites for tempoarlis muscle at the superior temporal line and inferior temporal line

Portions of the temporal bone

• squamous portion

• mastoid portion

Structures found on temporal bone

• external acoustic meatus

• mastoid forament

• mastoid process (attachment for sternocleidomastoid muscle)

• styloid procces

• mandibular fossa

• zygomatic process

Temporal Bone Fossas

• Temporal fossa

• Infratemporal fossa

• mandibular fossa

Zygomatic bone’s unique features

• zygomatic foramen

• frontal process

• temporal process

Sutures seen from norma lateralis

• coronal suture

• lambdoid suture

• squamous suture

• parietomastoid suture

• occipitomastoid suture

• spehnosquaosal suture

• sphenoparietal suture

• sphenofrontal suture

• sphenozygomatic suture

• zygomaticontemporal suture

• zygomaticonfrontal suture

• zygomaticomaxillary suture

Norma Lateralis openings visible and other notable features

Openings:

• eternal acoustic meatus

• mental foramen

• zygomatic foramen

Other notable features

• temporal fossa

• infratemporal fossa

• zygomatic arch

• asterion

• pterion

What does the parietal foramen contain and what views can see it?

Emissary veins

Norma verticalis & norma dorsalis

What does the mental foramen contain and what views can see it?

Mental nerve

Norma Lateralis

What does the zygomatic foramen contain and what views can see it?

zygomatic nerve

Norma lateralis

What does the external acoustic meatus contain and what views can see it?

conducts sound waves from auricle to tympanic membrane

Norma lateralis

What is contained in the mandibular foramen and what makes this foramen unique?

It contains the mandibular nerve, but it is not “visible from any normal skull view”

Bones visible from Norma Frontalis

• frontal bone

• 2 parietal bones

• 2 temporal bones

• 2 zygomatic bones

• 2 maxillary bones

• mandible

• 2 nasal bones

• spehnoid

• ethomoid

• 2 lacrimal bones

• vomer

• 2 inferior conchae

• 2 palatine bone - in orbit

Bones that compose the lateral wall of orbit

• greater wing of sphenoid

• zygomatic bone

“the Great Z

Bones that compose the floor of orbit

• Maxilla

• Palatine

• Zygomatic

“My Pal gets Z’s on the floor”

Bones that compose the medial wall of the orbit

• Ethmoid = thinnest

• lacrimal = thinner

• maxillary

• spheniod lesser wing

ELMS

Bones that compose the roof of the orbit

• Frontal bone

• lesser wing of sphenoid

Innervation of eye muscles

CN3, CN 4, CN6

Mnemonic for CN innervation of orbit muscles

(LR₆SO₄)₃ = Lateral Rectus CN6; Superior Oblique = CN4; all other muscles CN3

Orientation of CNs responsible for eye movement in certain directions (H chart thing)