Download CRANIUM OVERVIEW CRANIUM Two parts Neurocranium—bony

CRANIUM
OVERVIEW
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CRANIUM
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Two parts
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Neurocranium—bony case of the brain and its membranous coverings
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Contains proximal parts of the cranial nerves and brain vasculature
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Formed by a series of 8 bones
1. Frontal, ethmoidal, sphenoidal, and occipital
1. Ethmoidal is actually a large part of viscerocranium
2. Temporal and parietal that come in pairs
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Calvaria is the roof
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Cranial base is the floor
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Bones united by sutures
1. Sphenoid and occipital are actually united by hyaline cartilage in
childhood
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Viscerocranium—facial skeleton
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Develop from pharyngeal arches
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15 irregular bones here
1. Mandible, ethmoid, vomer (3 in the midline)
2. Maxillae, inferior nasal conchae, zygomatic, palatine, nasal, and
lacrimal bones (occur in pairs)
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PNEUMATIZED BONES
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Contain spaces for air—sinuses
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Frontal, temporal, sphenoid, and ethmoid bones
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Facial aspect
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In some adults, metopic suture in the middle of the glabella occurs
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Intersection of frontal and nasal bones is the nasion
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Used as a landmark to document abnormalities
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Supraorbital margin of frontal bone has a supraorbital foramen for passage of the
supraorbital nerve and vessels
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Just superior to subraorbital margin is superciliary arch—extends laterally on each side
from the glabella
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Zygomatic bones from prominences of cheeks
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Zygomaticofacial foramen pierces the lateral aspect of the bone
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Piriform aperture—anterior nasal opening in the cranium
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Bony nasal septum inside
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Nasal conchae are curved bony plates on either side
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Maxillae form the upper jaw—alveolar processes form tooth sockets
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Two maxillae are united at the intermaxillary suture
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Infraorbital foramen inferior to eachorbit for passage of the infraorbital nerve and
vessels
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Mandible
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Supports mandibular teeth
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Has a body and a ramus (vertical part)
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Mental foramina are inferior to second premolar teeth for mental nerves and
vessels
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Mental protuberance forms the prominence of the chin
1. Inferior to mandibular symphysis—osseous union between the two
halves of the mandible
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LATERAL ASPECT OF CRANIUM
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Main features are temporal fossa, external acoustic opening, mastoid process of
temporal bone—neurocranial part
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Infratemporal fossa, zygomatic arch, lateral aspects of maxilla and mandible—
viscerocranial part
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Temporal fossa is bounded by superior and inferior temporal lines superiorly
Zygomatic arch is formed by union of temporal process of the zygomatic bone and the
zygomatic process of the temporal bone
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Remember pterion
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Union of frontal, parietal, sphenoid, and temporal bones
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External acoustic opening is the entrance to external acoustic meatus (canal) which
leads to tympanic membrane
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Mastoid process of temporal bone
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Styloid process is anteromedial to mastoid process
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Slender and needle like
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Is part of temporal bone
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Infratemporal fossa is irregular space inferior and deep to zygomatic arch
OCCIPITAL ASPECT OF CRANIUM
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Composed of occiput, parts of parietal bones, and mastoid parts of temporal bones
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External occipital protuberance/inion
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External occipital crest descends from protuberance towards foramen magnum
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Has superior and inferior nuchal lines
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Lambda indicates the junction of sagittal and lambdoid sutures
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May also have sutural bones (accessory bones)
SUPERIOR ASPECT OF CRANIUM
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Broadens posteriorly at parietal eminences
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Frontal eminences may also be visible here
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Coronal suture separates frontal and parietal bones
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Sagittal suture separates parietal bones
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Lambdoid suture separates parietal and temporal bones from the occipital bone
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Bregma is where intersection or sagittal and coronal sutures is
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Vertex is most superior part of calvaria—near midpoint of sagittal sutures
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Parietal foramen is located posteriorly in the parietal bone near sagittal suture
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Emissary foramina transmit emissary veins connecting scalp veins to venous sinuses of
the dura mater
EXTERNAL SURFACE OF CRANIAL BASE
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Features alveolar arch of maxillae (free border of alveolar processes surrounding and
supporting maxillary teeth), palatine processes of maxillae, palatine, sphenoid, vomer,
temporal, and occipital bones
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Hard palate is formed by palatal processes of maxillae anteriorly and horizontal plates of
palatine bones posteriorly
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Posterior nasal spine—free posterior border of hard palate projects posteriorly
in the median plane as this
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Incisive fossa is here
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Right and left nasopalatine nerves pass from nose through a variable number of
incisive canals and foramina (may be bilateral or merged into a single
formation)
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Posterolaterally, greater and lesser palatine foramina occur
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Superior to the posterior edge of the palate are two large openings: choanae (posterior
nasal apertures), which are separated from each other by the vomer
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Sphenoid—irregular unpaired bone with 3 processes
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Greater wings, lesser wings, pterygoid processes
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Greater and lesser wings spread laterally from lateral aspects of the body of the
bone
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Greater wings have orbital, temporal, and infratemporal surfaces apparent in
facial, lateral, and inferior views of the exterior of cranium
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Pterygoid processes consist of lateral and medial pterygoid plates—extend
inferiorly on each side of the sphenoid from the junction of the body and
greater wings
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Groove for cartilaginous part of the pharyngotympanic (auditory) tube lies medial to
spine of sphenoid
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Inferior to greater wing of sphenoid and petrous part of temporal bone
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Depressions in squamous part of temporal bone are called mandibular fossae
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Accommodate mandibular condyles when mouth is closed
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Foramen magnum is seen—structures passing through it are spinal cord, meninges,
vertebral arteries, anterior and posterior spinal arteries, spinal accessory nerve (CN XI)
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Occipital condyles allow cranium to articulate with vertebral column
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Jugular foramen—opening between the occipital bone and petrous part of the temporal
bone
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Internal jugular vein, CN IX—CNXI emerge from the cranium from here
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Entrance to carotid canal for internal carotid artery is just anterior to the jugular
foramen
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Mastoid processes provide for muscle attachments
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Stylomastoid foramen, transmitting facial nerve (CNVII) and stylomastoid artery, lies
posterior to base of styloid process
INTERNAL SURFACE OF CRANIAL BASE
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Three large depressions—anterior, middle, and posterior cranial fossae
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Form the floor of the cranial cavity
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ANTERIOR CRANIAL FOSSA
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Inferior and anterior parts of frontal lobes occupy
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Formed by frontal bone anteriorly, ethmoid bone in the middle, and the body
and lesser wings of sphenoid posteriorly
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Frontal crest – median bony extension of the frontal bone
1. Foramen cecum of the frontal bone, which gives passage to vessels
during fetal development but is insignificant postnatally
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Crista galli – thick, median ridge of bone posterior to foramen cecum—projects
superiorly from the ethmoid bone
1. On each side of this is the cribriform plate of ethmoid – transmit CN I
nerves to olfactory bulbs of the brain
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MIDDLE CRANIAL FOSSA
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Central part is composed of sella turcica on the body of the sphenoid and large,
depressed lateral parts on each side
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Separated from anterior fossa by sphenoidal crests laterally and sphenoidal
limbus centrally
1. Sphenoidal crests are formed by posterior borders of the lesser wings
of sphenoid bones
2. Sphenoidal crests end in anterior clinoid processes
3. Limbus of sphenoid forms anterior boundary of the transversely
oriented prechiasmatic sulcus extending between right and left optic
canals
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Boundary between the middle and posterior cranial fossae is the superior
border of the petrous part of the temporal bone laterally and the dorsum sellae
of the sphenoid medially
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Sella turcica is the saddle-like bony formation on the upper surface of the
sphenoid, surrounded by anterior and posterior clinoid processes
1. Surround the hypophyseal fossa—bed of the pituitary gland
2. Sella turcica is composed of 3 parts
1. Tuberculum sellae—median elevation forming the posterior
boundary of the prechiasmatic sulcus and the anterior
boundary of the hypophysial fossa
2. Hypophysial fossa (pituitary fossa)—median depression in the
body of the sphenoid that accommodates the pituitary gland
3. Dorsum sellae—square plate of bone projecting superiorly
from the body of the sphenoid
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Forms the posterior boundary of the sella turcica and
its prominent superolateral angles make up the
posterior clinoid processes
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On each side of the body of the sphenoid, CRESCENT OF FOUR FORAMINA
1. Superior orbital fissure
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Located between the greater and lesser wings—opens
anteriorly into the orbit
2. Foramen rotundum
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Runs a horizontal course to an opening on the anterior aspect
of the root of the greater wing of the sphenoid into a bony
formation between the sphenoid, the maxilla, and the palatine
bones, the PTERYGOPALATINE FOSSA
3. Foramen ovale
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Opens inferiorly into the infratemporal fossa
4. Foramen spinosum
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Opens into infratemporal fossa in relationship to the spine of
the sphenoid
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Foramen lacerum
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Not part of the crescent of foramina
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Is an artifact of dried cranium
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Lies posterolateral to the hypophysial fossa
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Closed by cartilage plate in life
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Internal carotid artery and its accompanying sympathetic and venous
plexuses pass across the superior aspect of the cartilage and some
nerves traverse it horizontally, passing to a foramen in its anterior
boundary
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Groove for greater petrosal nerve
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Extending posteriorly and laterally from foramen lacerum is this on the
anterosuperior surface of the petrous temporal bone
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There is also a small groove for lesser petrosal nerve
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POSTERIOR CRANIAL FOSSA
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Largest and deepest of the 3 fossae lodges cerebellum, pons, and medulla
oblongata
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Formed mostly by occipital bone
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Dorsum sellae of the sphenoid marks its anterior boundary centrally
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Petrous and mastoid parts of temporal bones contribute to its anterolateral
walls
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Clivus
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Marked incline from dorsum sellae
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Internal occipital crest partly divides the fossa into cerebellar fossae
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Ends in internal occipital protuberance formed in relationship to the
confluence of the sinuses
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Jugular foramen is at the base of the petrous ridge of the temporal bone
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Transmits sigmoid sinus and several cranial nerves
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Anterosuperior to the jugular foramen is the internal acoustic meatus for the
facial and vestibulocochlear nerves (CN VIII) and labyrinthine artery
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Hypoglossal canal for hypoglossal nerve is superior to the anterolateral margin
of the foramen magnum
WALLS OF CRANIAL CAVITY
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Squamous part of temporal bone is fairly thin—usually places of skull covered by
muscles are thinner
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Most bones of calvaria consist of internal and external tables of compact bone,
separated by diploe.
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Diploe is cancellous bone containing red bone marrow during life, through which
run canals formed by diploic veins
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Internal table of bone is thinner than the external table
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Some areas have only a thin plate of compact bone with no diploe
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Walls are buttressed in some places to stand up to the tension forces produced by
muscles of mastication
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FRONTONASAL BUTTRESS
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Extends from region of canine tooth between the nasal and orbital
cavities to the central frontal bone
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ZYGOMATIC ARCH—LATERAL ORBITAL MARGIN BUTTRESS
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From region of the molars to the lateral frontal and temporal bones
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OCCIPITAL BUTTRESSES
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Regions
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Transmit forces received lateral to the foramen magnum from the
vertebral column
of head
Face is divided into 8 regions
Names of the regions correspond to the underlying bones
Frontal, parietal, occipital, temporal, and mastoid regions
Viscerocranial portion of the head includes facial region, divided into five bilateral and three
median regions related to superficial features (oral and buccal regions), to deeper soft tissue
formations (parotid region), and to skeletal features (orbital, infra-orbital, nasal, zygomatic,
mental regions)