Skull Bone Composition: Neurocranium

Skull Bone Composition

• Composed of flattened and irregular bones fitted together immovably by joints, known as sutures.
• Mandible (lower jaw) is an exception to this rule and is a freely movable bone

Neurocranium

• The skull is divided into two major parts, one being the Neurocranium
• The Neurocranium consists of 8 bones

Bones of the Neurocranium

• Frontal (1)
• Occipital (1)
• Parietals (2); these are paired bones
• Temporals (2); these are paired bones
• Sphenoid (1)
• Ethmoid (1)

Temporal Bones

• Has receptors for hearing + head acceleration, including receptors sensing linear and angular head movement

Sphenoid Bone

• Complex structure with a body in the middle and wings laterally
• Contains many foramina (holes)

Ethmoid Bone Location and Function

• Found in the roof of the nasal cavity.
• Extends downwards to contribute to the nasal septum and the two lateral walls of the nasal cavity

Parietal Bone Features

• Forms the sides and roof of the cranium
• Irregularly quadrilateral in shape
• Has 2 surfaces, 4 borders, and 4 angles
• It is a paired bone

Frontal Bone Divisions

• Anterior-superior part of the skull, divided into two portions: squama and orbital
• Squama: Flat, forehead portion
• Orbital (horizontal): Forms part of the orbit

Frontal Bone Connections

• The squamous part connects with the squamous border of the parietal bone
• Has sinuses

Occipital Bone Characteristics

• Postero-inferior portion of the cranium
• Features an oval aperture termed the foramen magnum
• The foramen magnum facilitates communication between the cranial cavity and the vertebral canal

Occipital Bone Internal Surface

• Is divided into two fossae: Upper and Lower
• Upper: lodges the brain (cerebrum)
• Lower: accommodates the cerebellum

Atlas Articulation with Occipital Bone

• The occipital bone has condyles that articulate with the atlas
• This joint facilitates nodding movements

Sphenoid Bone: Internal Features

• Has a deep depression called the sella turcica on its internal surface
• The deepest part of this depression is the hypophysial fossa

Temporal Bone Traits

• The second most complex bone in the skull
• Located on the sides of the skull
• Contains the organ of hearing and equilibrium
• It has 3 major parts: squamous, petrous and mastoid process
• Temporomandibular joint: the joint between the temporal bone and the mandible

Ethmoid Bone Characteristics

• Is also a pneumatic bone
• Anterior part of base of cranium and the roof of the nose

Ethmoid Bone Parts

• Horizontal part / Cribriform plate: Forms the anterior part.
• Cribriform plate has perforations (foramina) for the passage of olfactory nerves
• Perpendicular plate: Constitutes part of nasal septum
• Superior and middle nasal conchae: Downward extensions on the sides of the septum

Splanchnocranium

• Also known as the visceral cranium, or the bones of the face
• Contains:
• Nasals (2)
• Maxillae (2)
• Zygomatics (2)
• Palatines (2)
• Conchae
• Vomer
• Lacrimals (2)
• Mandible (1)

Vomer Bone

• Located between the nasal cavities.
• It's thin, roughly triangular and contributes to the lower portion of the nasal septum

Mandible Bone

• The largest and strongest bone of the face
• Comprised of a body and rami
• Body: superior border
• Rami: means branch; there are 2

Maxilla Characteristics

• These are paired bones that form boundaries, roof of the mouth, floor and lateral wall of the nose, floor of orbit
• The body is pyramidal in shape
• Contains the maxillary sinus

Maxilla Key Features

• Contains largest sinus
• Palatine process forms part of the floor of the nose and roof of the mouth (palate)

Palatine Bone Details

• Located in the posterior part of the nasal cavity
• Situated between the maxilla and sphenoid bones Contributes to the walls of two cavities: the floor and lateral wall of the nasal cavity, as well as the roof of the mouth (palate)

Zygomatic Bone Properties

• Lateral part of the face
• Forms the prominence of the cheek
• Part of the lateral wall and the floor of the orbit (infralateral part of it)

Nasal Bone Traits

• Located on the dorsum of the nose

Lacrimal Bone Traits

• Located on the anteromedial wall of the orbit

Sutures

• These are articulations where continuous margins of bones are united by a thin layer of fibrous tissue
• Coronal Suture: Between the parietal and frontal bones
• Lambdoidal Suture: Between the parietal bones and occipital bone
• Sagittal Suture: Between the two parietal bones
• Squamosal Suture: Between the temporal bone and parietal bone
• Occipitomastoid Suture: Between the occipital and temporal bones
• Sphenosquamosal Suture: Between the temporal bone and sphenoid bone

Cranial Fossae

• Anterior cranial fossa
• Middle Cranial Fossa
• Posterior cranial fossa

Cranial Intersection Points and Areas

• Bregma: Midline point where the coronal and sagittal sutures intersect
• Lambda: Midline point where the sagittal and lambdoidal sutures intersect Glabella: Slight elevation in the midline of the forehead, between the superciliary arches and above the nasofrontal suture
• Pterion: Point of intersection between the frontal, sphenoid, parietal, and temporal bones; weak
• Nasion: Point of intersection between the frontonasal suture and the midsagittal plane
• Gnathion: Most anterior and lowest median point on the border of the mandible

Fontanelles

• In newborns, ossification is not complete in certain regions
• This results in a soft region
• Those soft regions are called fontanelles, the biggest is located in the Anterior part of the skull Another type of fontanelle: posterior

Norma Superior

• Skull view from superior/vertical direction
• Coronal, sagittal, and lambdoid sutures can be seen

Norma Frontalis

• Skull view from norma facialis/frontalis direction
• Piriform aperture: Surrounded by the maxilla and nasal bones; opens into the nasal cavities
• Orbital fossa

Norma Lateralis

• Skull view from lateral side
• Vertex: Uppermost point
• Occiput: Most posterior point
• Gonion: Tip of the angle of mandible
• Temporal fossa: Shallow depression formed by squamous part of temporal and parietal; bordered inferiorly by zygomatic arch

Norma Occipitalis

• Skull View from Posterior Side
• External occipital protuberance: Most prominent elevation in the middle
• Lambdoid suture
• Interparietal bones; between parietal and occipital
• Sutural bones (small bones): Seen in some people when bones do not fuse

Norma Basalis

• Skull View from Inferior Direction
• Hard Palate - bony part of palate
• Median palatal suture

Sutures and Foramen

• Transverse Palatal Suture
• Incisive Foramen
• Jugular foramen: One of the largest, located between the occipital and temporal bones
• Foramen lacerum: Also big, located between occipital, temporal and sphenoid bones
• Choana: Posterior opening of nasal cavity

Calvaria

• The upper part of the neurocranium, also called the skull cap
• Composed of sections of the frontal, parietal, and occipital bones Removing Calvaria: exposes the base of the cranial cavity (cranial vault)

Cranial Vault

• Three fossae observed: anterior, middle, posterior cranial fossae

Anterior Cranial Fossa

• Base Components:
  • Anteriorly: orbital part of frontal bone
  • Middle: cribriform plate of ethmoidal bone
  • Posteriorly: lesser wings and antero-superior part of sphenoid bonePosterior Border:- posterior borders of lesser wings (of sphenoid bone)
  • Anterior Clinoid processes

Middle Cranial Fossa

• Anterior Border: posterior borders of lesser wings, anterior clinoid fossa
• Posterior border: dorsum sellae of sphenoid bone, superior margin of petrous part of temporal bone

Posterior Cranial Fossa

• Anterior border: dorsum sellae of sphenoid bone, superior margin of petrous part of temporal bone
• Middle: foramen magnum foramen is observed

Infratemporal Fossa

• Infero-medial to zygomatic arch
• Medial to ramus of mandible

Pterygopalatine Fossa

• Medial to infratemporal fossa
• Connects to infratemporal fossa through pterygomaxillary fissure

Pterygopalatine Fossa: Connections, Lateral

• Connects to infratemporal fossa through pterygomaxillary fissure
• Connections of Pterygopalatine fossa wl other fossae

Pterygopalatine Fossa: Connections, Medial

• Connects to nasal cavity through sphenopalatine foramen

Pterygopalatine Fossa: Connections, Superior

• Connects to middle cranial fossa through foramen rotundum and pterygoid canal

Pterygopalatine Fossa: Connections, Antero-Superior

• Connects to orbit through inferior orbital fissure
• If the direction is downwards, reaches posterior part of palate (greater and lesser palatine foramina)

Orbit Characteristics

• Bony cavity containing the eyeball and related structures
• Consists as a roughly pyramidal shape

Orbital Bone Contributions

• Frontal bone: forms the superior margin and part of the root of orbit Zygomatic bone: contributes to lateral wall and part of floor of orbit
• Maxilla: forms the floor
• Palatine bone: provides posterior part of the floor and medial wall
• Lacrimal bone: contributes part of medial wall
• Ethmoid bone: contributes to medial wall and part of roof
• Sphenoid bone: forms the posterior part and contributes to lateral wall of roof

Orbit Connections to Other Spaces

• Middle cranial fossa through superior orbital fissure and optic canal
• Pterygopalatine fossa through inferior orbital fissure
• Nasal cavity through anterior and posterior ethmoid foramina (tiny foramina)

Nasal Cavity Septum Separation

• Right and left nasal cavities are separated by the nasal septum
• Each cavity opens into pharynx through choanas

Nasal Formers

• Perpendicular plate of ethmoid bone: Postero-superior
• Vomer: Postero-inferior
• Septal Cartilage: Anterior

Elevated Areas

• These elevations are called conchae and they are located on the lateral wall of nasal cavity

Superior nasal concha: part of the ethmoid Middle nasal concha: Bone Inferior nasal concha: separate

• Spaces between conchaes are called meatus; found infero-laterally to each concha: superior, middle, and inferior

Skull of Newborns

• Incomplete ossification
• Some soft structures can be palpated, called fonticulus(Anterior Fonticulus).
• Anterior Fonticulus: the closes the latest (6-24 months)

Fonticulus

• The other soft structures than can be palpated are
• Posterior Fonticulus (closes ~1-6 months)
• Anterolateral / Sphenoid fonticulus close shortly
• Posterolateral / mastoid fonticulus (after birth