Cranium - Module 7

Cranial bones of the skull

Cranial bones

- Temporal

- Parietal

- Occipital

- Frontal

Ethmoid

Sphenoid

Cranial Sutures

Lateral

Superior

- Coronal suture

- Sagittal suture

Posterior

- Lambdoid structure

Infant Skull: Pre-sutures

"Soft spots" in infant skulls

Close at various times

- Posterior fontanelle (sagittal & lambdoid suture): by 6 months

- Anterior fontanelle (frontal & coronal sutures): ~middle of second year

Craniosynostosis

Premature fusing of sutures

Frontal Bone Description

Forms anterior part of brain case

Vertical plate contributes to forehead

Horizontal plate contributes to roof of orbit and nasal cavities

Zygoamtic process

Lateral to orbital surfaces for articulation with zygomatic bone

Frontal Bone - Ethmoid Notch

Midline notch called ethmoid notch articulates with ethmoid bone

Parietal Bones Description

Form most of rounded roof of cranium

Each bone roughly quadrilateral

Attachments

- Anterior: frontal bone at coronal suture

- Medial: midline at sagittal suture with other parietal bone

- Posterior: occipital bone at lambdoid suture

Occipital Bone Description

Inferior and posterior portion of cranium

- Forms lower and back portion of cranium

- Articulates with parietal bones at lambdoid suture

Includes foramen magnum

Includes occipital condyles

Occipital Bone Features

Occipital Condyles

- Lateral to foramen magnum

- Articulate with superior facets of

C1

Just posterior to each condyle

is a condylar fossa

- Recess for superior articular

processes of atlas when head

tilted sharply backward

Temporal Bones Description

Paired bones forming most of lateral base and sides of brain case

Each bone has 3 parts

- Squamous part

- Includes zygomatic process

- Petrous part

- Tympanic part

- Includes styloid process

Temporal Bone Features

Zyogamtic process

External auditory meatus

Mastoid process

Temporomandibular joint

Temporal Bone - inferior view

Temporal Bone - Squamous Part

Lateral, anterior, superior aspect of bone

Zygomatic process

- Forms zygomatic arch with temporal

process of zygomatic bone

Mandibular fossa

- Articulates with condylar process of

mandible

- Part of temporomandibular joint (TMJ)

Temporal Bone - Petrous Part

Sometimes called petromastoid part

At base of skull

Houses cochlea and inner ear

Includes mastoid process

- Numerous muscle attachments

Temporal Bone - Tympanic Portion

Anterior to mastoid process and between squamous

and petrous portions

Contains part of external auditory meatus

- Essentially the area immediately around the opening

- Remainder in Petrous portion

Includes styloid process

- Numerous muscle attachments

Ethmoid Description

Although regarded as cranial bone, also contributes to facial skeleton

Hangs down from ethmoid notch of frontal bone between orbital plates of frontal bone

Loosely behind and above the maxilla

Contributes to the

- walls of orbit

- lateral walls of nasal cavity

- bony nasal septum

Ethmoid - Frontal

Cribiform plate

Perpendicular plate

Superior and Middle Cochae

Cribiform plate

Horizontal plate that separates cranial and nasal cavities

Perpendicular plate

Thin plate directed inferiorly from underside of cribiform plate

Forms upper portion of bony nasal septum

Superior and Middle Conchae

Two lateral plates house superior and middle nasal concha

Form lateral walls of nasal

cavity

Complex curvature is to increase surface area to warm and humidify air

Ethmoid - Oblique Superior and Inferior

Cribiform plate attaches to

the ethmoid notch

Ethmoid - Paramedian View of Nasal

Cavity

Vomer

Ethmoid (perpendicular plate)

Cartilaginous Septum

Inferior nasal concha

Middle nasal concha (of ethmoid)

Superior nasal concha (of ethmoid)

Sphenoid Bone Description

Located at base of skull, behind ethmoid, and in front of foramen magnum

Consists of

- Body

- Lesser wings

- Greater wings

- Pterygoid plates

Sphenoid articulates with all bones of the cranium and 3 facial skeleton bones

Sphenoid Bone Parts

Body

Lesser Wings

Greater Wings

Pterygoid Processes

Body

Forms posterior wall of nasal cavity

Lesser Wings

Contribute to anterior cranial fossa and superior wall of orbit

Greater Wings

Contribute to middle cranial fossa and posterior ½ of lateral

wall of orbit

Pterygoid Processes

Medial and lateral

Attachment of pterygoid

muscles

Sphenoid Bone - Lateral / Superior

Hamulus

Medial Pterygoid Plate

Lateral Pterygoid Plate

Sphenoid Bone - Superior/Inferior Views

Superior Views

- Body

- Lesser wing

- Greater wing

Inferior View

- Pterygoid processes

Sphenoid Bone - External View

Greater wing

Pterygoid process

Bones of the Orbit

Ethmoid

Frontal

Sphenoid

Lacrimal

Maxilla

Zygomatic

Bones of the Nasal Cavity

Inferior nasal concha

Middle nasal concha (of ethmoid)

Superior nasal concha (of ethmoid)

What do the bones of the cranium contain?

a portion of the structure surrounding the brain

What are the ethmoid and sphenoid bones purpose?

define many of the complex passageways of the nasal cavity as well as some of the sinuses

What are the vomer, inferior concha, palatine, and maxilla purposes?

define the lower surfaces of the nasal cavity

How does the occipital bone articulate?

with the vertebral column at the occipital condyles

What are the sphenoid and temporal bones purpose?

have processes for muscular attachment

What is the orbit?

shaped by the frontal, ethmoid, sphenoid bones of the cranium as well as the lacrimal,

maxilla and zygomatic bones of the facial skeleton