Skull Anatomy and Structure

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Questions and Answers

What is the approximate volume range of an adult cranial cavity?

1300 to 1500 cubic centimeters or about 50 fluid ounces

Which of the bones listed are paired facial bones?

zygomatic bones, lacrimal bones, nasal bones, inferior nasal conchae, and palatine bones

What is the function of the major foramina of the cranial and facial bones?

serve as passageways for blood vessels and nerves

How many bones form the skull?

14 Signup and view all the answers

Which bones are unpaired in the skull?

vomer and mandible Signup and view all the answers

What is the benefit of the skull being made of multiple smaller bones rather than one big bone?

The benefit is not specified in the text, but it could be inferred that multiple smaller bones allow for greater flexibility and adaptation. Signup and view all the answers

What is the cranial cavity also known as?

endocranium Signup and view all the answers

What is the purpose of studying the individual skull bones in detail?

to understand the complex nature of the skull Signup and view all the answers

What is the main distinction between cranial bones and facial bones in the skull?

Cranial bones form the cranium, which surrounds and encloses the brain, whereas facial bones form the face and protect the entrances to the digestive and respiratory systems. Signup and view all the answers

What is the calvaria, and what bones comprise it?

The calvaria is the roof of the cranium, composed of the superior part of the frontal bone, the parietal bones, and a small part of the occipital bone. Signup and view all the answers

What is the function of the facial bones in the skull?

Facial bones give shape and individuality to the face, form part of the orbit and nasal cavities, support the teeth, and provide for the attachment of muscles involved in facial expression and mastication. Signup and view all the answers

How many bones make up the skull, and what kind of joints connect them?

The skull is composed of 22 bones, connected by sutures, a type of fibrous joint. Signup and view all the answers

What is the base of the cranium composed of?

The base of the cranium is composed of portions of the frontal, ethmoid, sphenoid, occipital, and temporal bones. Signup and view all the answers

What is the main difference between the cranial and facial bones in terms of their function?

Cranial bones protect and enclose the brain, whereas facial bones support the entrances to the digestive and respiratory systems, and are involved in facial expression and mastication. Signup and view all the answers

What is the term for the study of the anatomy of the skull?

There is no specific term mentioned in the text for the study of the anatomy of the skull. Signup and view all the answers

What is the term for the process of chewing?

The term for the process of chewing is mastication. Signup and view all the answers

What is the term for the passageway of small veins between the brain and the scalp, located along the posterior one-third of the sagittal suture?

parietal foramen or paired parietal foramina Signup and view all the answers

What bone forms the lateral boundaries of the nasal cavity and holds the teeth?

maxilla Signup and view all the answers

What is the term for the thin ridge of bone that divides the nasal cavity into left and right halves?

nasal septum Signup and view all the answers

What is the term for the scroll-shaped bones along the inferolateral walls of the nasal cavity?

inferior nasal conchae Signup and view all the answers

What is the term for the articulation between the frontal and parietal bones?

coronal suture Signup and view all the answers

What is the term for the suture that connects the left and right parietal bones along the midline of the skull?

sagittal suture Signup and view all the answers

What is the term for the prominence on the posterior aspect of the skull?

external occipital protuberance Signup and view all the answers

What is the term for the lines that arc across the surface of the parietal and frontal bones, marking the attachment sites for the temporalis muscle?

superior and inferior temporal lines Signup and view all the answers

What is the term for the region where the sphenoid bone articulates with the frontal, parietal, and temporal bones?

pterion Signup and view all the answers

What is the term for the bone that forms the lower jaw?

mandible Signup and view all the answers

What structure is the most anterior in an inferior (basal) view of the skull?

hard palate Signup and view all the answers

What are the medial and lateral plates of the sphenoid bone that form a pterygoid process?

pterygoid plates Signup and view all the answers

What are the internal openings of the nasal cavity called?

choanae Signup and view all the answers

What foramen is an opening between the temporal and occipital bones that provides a passageway for the internal jugular vein and several nerves?

jugular foramen Signup and view all the answers

What is the largest foramen of all in the cranial base?

foramen magnum Signup and view all the answers

What plate of the ethmoid bone has numerous perforations that provide passageways for the olfactory nerves?

cribriform plate Signup and view all the answers

What is the midline elevation on the cribriform plate to which the cranial dural septa of the brain attach?

crista galli Signup and view all the answers

What is the depression between the greater and lesser wings of the sphenoid bone that contains the pituitary gland?

hypophyseal fossa Signup and view all the answers

What are the lateral expansions of the sphenoid bone called?

greater and lesser wings Signup and view all the answers

What is the bony enclosure around the hypophyseal fossa called?

sella turcica Signup and view all the answers

What is the significance of the internal occipital protuberance in the occipital bone?

It is an internal landmark of the occipital bone. Signup and view all the answers

What is the function of the frontal crest on the frontal bone?

It is an attachment site for meninges to help stabilize the brain within the skull. Signup and view all the answers

Which nerve passes through the internal acoustic meatus?

The facial nerve (CN VII) and the vestibulocochlear nerve (CN VIII). Signup and view all the answers

What is the significance of the parietal foramen on the parietal bone?

It is an associated passageway. Signup and view all the answers

What is the function of the zygomatic process on the frontal bone?

It articulates with the zygomatic bone. Signup and view all the answers

Which bones form the inferolateral wall of the skull?

The temporal bones. Signup and view all the answers

What is the significance of the internal aspect of the cranium?

It has large grooves formed from impressions of the dural venous sinuses of the brain. Signup and view all the answers

What is the function of the squamous part of the frontal bone?

It is an attachment site for scalp muscles. Signup and view all the answers

What is the primary function of the petrous part of the temporal bone?

Protects sensory structures in the inner ear Signup and view all the answers

What is the purpose of the nasal conchae in the nasal cavity?

Increases airflow turbulence to facilitate moistening and cleaning of inhaled air by nasal mucosa Signup and view all the answers

What is the function of the sphenoidal sinuses?

Lighten bone, moisten inhaled air, and give resonance to voice Signup and view all the answers

What is the significance of the cribriform plate in the ethmoid bone?

Contains cribriform foramina for passageway of olfactory nerves (CN I) Signup and view all the answers

What is the function of the hypophyseal fossa in the sphenoid bone?

Depression that houses the pituitary gland Signup and view all the answers

What is the role of the mandibular notch in the mandible bone?

U-shaped depression between coronoid and condylar processes Signup and view all the answers

What is the primary function of the zygomatic process of the temporal bone?

Articulates with zygomatic bone to form zygomatic arch Signup and view all the answers

What is the purpose of the inferior nasal conchae in the nasal cavity?

Increases airflow turbulence in the nasal cavity Signup and view all the answers

What is the significance of the perpendicular plate of the ethmoid bone?

Forms superior part of nasal septum Signup and view all the answers

What is the role of the lacrimal groove in the lacrimal bone?

Contains nasolacrimal duct Signup and view all the answers

What is the primary location of the ethmoid and sphenoid bones in the skull?

Deep to other bones. Signup and view all the answers

What is the etiology of cleft lip and cleft palate?

Multifactorial, involving both genetic and environmental factors. Signup and view all the answers

What is the term used to describe an asymmetric head shape, usually caused by unilateral coronal craniosynostosis or asymmetric lambdoid synostosis, where one part of the skull has an oblique flattening?

Plagiocephaly Signup and view all the answers

What are the three curved depressions in the floor of the cranial cavity?

Anterior, middle, and posterior cranial fossae. Signup and view all the answers

Which bones form the anterior cranial fossa?

Frontal bone, ethmoid bone, and lesser wings of the sphenoid bone. Signup and view all the answers

What is the condition called when the sagittal suture fuses prematurely, resulting in an elongated, narrow skull shape?

Scaphocephaly or dolichocephaly Signup and view all the answers

What type of joints form the boundaries between the cranial bones?

Immovable fibrous joints. Signup and view all the answers

What is the term used to describe the air-filled chambers within the frontal, ethmoid, and sphenoid bones and the maxillae that open into the nasal cavities?

Paranasal sinuses Signup and view all the answers

What is the benefit of the paranasal sinuses in the skull?

They help to humidify and warm inhaled air, reduce the weight of the skull bones, and provide resonance to the voice. Signup and view all the answers

What is the function of the sutures in the skull?

To connect cranial bones firmly together. Signup and view all the answers

What is the primary reason for the increased incidence of plagiocephaly in the United States since the 1990s?

The Back to Sleep Campaign, which encourages parents to place children on their backs to sleep. Signup and view all the answers

What is the name of the suture that extends laterally across the superior surface of the skull?

Coronal suture. Signup and view all the answers

Which suture extends like an arc across the posterior surface of the skull?

Lambdoid suture. Signup and view all the answers

What is the term used to describe the premature fusion of the coronal suture, which causes the skull to be abnormally short and wide?

Coronal synostosis Signup and view all the answers

What is the function of the mucous membrane lining in the paranasal sinuses?

To humidify and warm inhaled air Signup and view all the answers

What is the significance of the cranial fossae in relation to the brain?

They house different parts of the brain. Signup and view all the answers

What is the relationship between the cranial bones and the sutures?

Cranial bones articulate at the sutures. Signup and view all the answers

What is the significance of the paranasal sinuses in the voice?

They provide resonance to the voice Signup and view all the answers

What is the sagittal suture and where is it located?

The sagittal suture is the site where the right and left parietal bones articulate and it extends between the coronal and lambdoid sutures along the midsagittal plane. Signup and view all the answers

What is the significance of sutural bones in the skull?

Sutural bones represent independent bone ossification centers and are most common and numerous in the lambdoid suture. Signup and view all the answers

How do osteologists estimate the approximate age at death of an individual?

By examining the extent of suture closure in the skull. Signup and view all the answers

What is the nasal complex composed of?

Bones and cartilage that enclose the nasal cavity and the paranasal sinuses. Signup and view all the answers

What is the function of the orbits in the skull?

To enclose and protect the eyes and the muscles that move them. Signup and view all the answers

What is craniosynostosis?

The premature fusion or closing of one or more of the cranial sutures. Signup and view all the answers

Why are sutures important in the skull?

They allow the cranium to grow and expand during childhood. Signup and view all the answers

What is the significance of the lambdoid suture?

It is the site where the parietal bones and the occipital bone articulate, and its shape resembles the Greek letter lambda. Signup and view all the answers

What is the squamous suture?

The site where the temporal bone and the parietal bone of that side articulate, with the squamous part of the temporal bone typically overlapping the parietal bone. Signup and view all the answers

What happens to the sutures in adulthood?

They typically fuse and are obliterated as the adjoining bones fuse. Signup and view all the answers

What is the primary structure that passes through the foramen spinosum in the greater wing of the sphenoid bone?

Middle meningeal vessels Signup and view all the answers

Which cranial foramen is located between the temporal bone, sphenoid bone, and occipital bone, and what structure passes through it?

Foramen lacerum; no structures pass through it Signup and view all the answers

What is the purpose of the stylomastoid foramen, and which nerve passes through it?

The stylomastoid foramen allows the facial nerve (CN VII) to pass through. Signup and view all the answers

What are the two large openings within each orbit called, and which bones form them?

The superior orbital fissure and the inferior orbital fissure; formed from a complex articulation of multiple skull bones Signup and view all the answers

Which bone forms the forehead, and what are the bony ridges superior to the orbits called?

The frontal bone; superciliary arches (or brow ridges) Signup and view all the answers

What is the landmark area called between the orbits and superior to the nasal bones?

The glabella Signup and view all the answers

What is the primary structure that passes through the jugular foramen?

Internal jugular vein; glossopharyngeal nerve (CN IX); vagus nerve (CN X); accessory nerve (CN XI) Signup and view all the answers

What are the two bones that form the nasal bridge?

The left and right nasal bones Signup and view all the answers

What is the primary structure that passes through the optic canal?

The optic nerve (CN II) Signup and view all the answers

What are the two foramina in the palatine bone that allow palatine vessels and nerves to pass through?

The greater and lesser palatine foramina Signup and view all the answers

What is the significance of the pterion in the skull?

It is the H-shaped set of sutures of the four articulating bones. Signup and view all the answers

What is the function of the zygomatic arch?

It provides a bony prominence for muscle attachment and forms the cheekbone. Signup and view all the answers

What is the significance of the mastoid process?

It serves as an attachment site for the sternocleidomastoid muscles. Signup and view all the answers

What is the role of the styloid process?

It serves as an attachment site for several hyoid and tongue muscles. Signup and view all the answers

What is the function of the perpendicular plate of the ethmoid bone?

It forms the posterosuperior portion of the nasal septum. Signup and view all the answers

What is the significance of the vomer?

It forms the posteroinferior portion of the nasal septum. Signup and view all the answers

What is the function of the sphenoid bone in the nasal cavity?

It contains the sphenoidal sinus, which is an open space within the bone. Signup and view all the answers

What is the significance of the palatine process of the maxillae?

It forms part of the hard palate, which acts as both the floor of the nasal cavity and a portion of the roof of the mouth. Signup and view all the answers

What is the function of the ethmoid bone in the skull?

It serves as the division between the anterior floor of the cranial cavity and the roof of the nasal cavity. Signup and view all the answers

What is the significance of the sagittal sectional view of the skull?

It reveals bones that form the cranial cavity and the nasal cavity. Signup and view all the answers

Study Notes

The Skull

The skull is composed of 22 bones, which can be divided into two main categories: cranial bones and facial bones.
Cranial bones form the cranium, which surrounds and protects the brain. There are 8 cranial bones.
- The calvaria (roof of the cranium) is composed of the superior part of the frontal bone, the parietal bones, and a small part of the occipital bone.
- The base of the cranium is composed of portions of the frontal, ethmoid, sphenoid, occipital, and temporal bones.
Facial bones form the face and give shape and individuality to the face. There are 14 facial bones.
- They protect the entrances to the digestive and respiratory systems, support the teeth, and provide for the attachment of muscles involved in facial expression and mastication (chewing).

Cavities of the Skull

The cranial cavity (or endocranium) encloses, protects, and supports the brain.
The skull also forms and has several smaller cavities, including:
- Orbits (eye sockets)
- Oral cavity
- Nasal cavity
- Paranasal sinuses

Landmark Features of the Skull

The skull has numerous bone markings, such as canals, fissures, and foramina that serve as passageways for blood vessels and nerves.
Key landmarks include:
- Foramen magnum: a large opening at the base of the skull through which the spinal cord enters the cranial cavity.
- Optic canal: a passageway for the optic nerve (CN II) that extends from the eye to the brain.
- Internal acoustic meatus (or internal auditory canal): a passageway for the facial nerve (CN VII) and the vestibulocochlear nerve (CN VIII).

Views of the Skull

Anterior view: shows the frontal bone, nasal bones, maxillae, and mandible.
Superior view: shows the frontal bone, parietal bones, and occipital bone.
Posterior view: shows the occipital, parietal, and temporal bones.
Lateral view: shows one parietal bone, temporal bone, and zygomatic bone, as well as part of the maxilla, mandible, frontal bone, and occipital bone.
Inferior view: shows the hard palate, the sphenoid bone, parts of the temporal bone, and the occipital bone with its foramen magnum.

Internal View of the Cranial Base

The internal view of the cranial base is revealed when the top of the skull is cut and removed.
Key features include:
- Cribriform plate of the ethmoid bone, which has numerous perforations called cribriform foramina that provide passageways for the olfactory nerves (CN I).
- Sphenoid bone, which is often referred to as a "bridging bone" because it unites the cranial and facial bones.
- Pituitary gland, which is suspended inferiorly from the brain into a prominent midline depression between the greater and lesser wings of the sphenoid bone called the hypophyseal fossa.### Cranial Bones
Cranial bones include frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones
Each bone has distinct features and functions:
- Frontal bone:
  - Forms superior and anterior parts of the skull
  - Part of anterior cranial fossa and orbit
  - Features: frontal crest, frontal sinuses, orbital part, squamous part, supraorbital margin, zygomatic process
- Parietal bone:
  - Forms most of lateral and superior walls of the skull
  - Features: superior and inferior temporal lines, parietal eminence
- Temporal bone:
  - Forms inferolateral wall of the skull
  - Part of middle cranial fossa
  - Features: petrous part, squamous part, tympanic part, mastoid process, styloid process, zygomatic process, mandibular fossa, articular tubercle
- Occipital bone:
  - Forms posteroinferior part of the skull
  - Part of posterior cranial fossa
  - Features: external occipital crest, external occipital protuberance, inferior and superior nuchal lines, occipital condyles
- Sphenoid bone:
  - Forms part of base of the skull
  - Part of posterior part of orbit and anterior and middle cranial fossae
  - Features: hypophyseal fossa, body, sella turcica, optic groove, medial and lateral pterygoid plates, lesser wings, greater wings
- Ethmoid bone:
  - Forms part of anterior cranial fossa
  - Part of nasal septum, roof, and lateral walls of nasal cavity
  - Part of medial wall of orbit
  - Features: cribriform plate, crista galli, ethmoidal labyrinths, ethmoidal sinuses, nasal conchae

Facial Bones

Facial bones include zygomatic, lacrimal, vomer, inferior nasal conchae, palatine, and maxilla bones
Each bone has distinct features and functions:
- Zygomatic bone:
  - Forms cheek and lateral part of orbit
  - Features: frontal process, temporal process, maxillary process
- Lacrimal bone:
  - Forms part of medial wall of orbit
  - Feature: lacrimal groove
- Vomer:
  - Forms inferior and posterior part of nasal septum
  - Features: ala, vertical plate
- Inferior nasal conchae:
  - Projects medially from lateral walls of nasal cavity
  - Increases airflow turbulence in nasal cavity
- Palatine bone:
  - Forms posterior part of hard palate
  - Part of nasal cavity and orbit wall
  - Features: horizontal plate, perpendicular plate
- Maxilla:
  - Forms anterior portion of face
  - Part of hard palate, inferior parts of orbits, and walls of nasal cavity
  - Features: anterior nasal spine, alveolar process, frontal process, infraorbital margin, maxillary sinus, orbital surface, palatine process, zygomatic process

Cranial Fossae

Cranial fossae are three curved depressions in the cranial cavity
Each fossa has distinct features and functions:
- Anterior cranial fossa:
  - Shallowest of the three depressions
  - Formed by frontal bone, ethmoid bone, and lesser wings of sphenoid bone
  - Houses frontal lobes of the brain
- Middle cranial fossa:
  - Inferior and posterior to anterior cranial fossa
  - Formed by posterior edge of lesser wings of sphenoid bone and anterior region of petrous part of temporal bone
  - Houses temporal lobes of the brain and pituitary gland
- Posterior cranial fossa:
  - Most inferior and posterior cranial fossa
  - Extends from posterior region of petrous part of temporal bone to occipital bone
  - Houses part of brainstem and cerebellum

Sutures

Sutures are immovable fibrous joints that form boundaries between cranial bones
Each suture has distinct features and functions:
- Coronal suture:
  - Extends laterally across superior surface of skull
  - Articulation between frontal bone and parietal bones
- Lambdoid suture:
  - Extends like an arc across posterior surface of skull
  - Articulation between parietal bones and occipital bone
- Sagittal suture:
  - Extends between coronal and lambdoid sutures
  - Articulation between right and left parietal bones
- Squamous suture:
  - Site where temporal bone and parietal bone articulate
- Sutural bones (Wormian bones):
  - Independent bone ossification centers
  - Most common in lambdoid suture

Orbital and Nasal Complexes, Paranasal Sinuses

Orbital complex consists of seven bones that form each orbit: sphenoid, frontal, zygomatic, maxilla, palatine, ethmoid, and lacrimal bones
Nasal complex consists of bones and cartilage that enclose nasal cavity and paranasal sinuses
Paranasal sinuses are air-filled chambers within frontal, ethmoid, and sphenoid bones and maxillae
Each sinus has distinct features and functions:
- Ethmoidal sinus:
  - Lightens bone, moistens inhaled air, and gives resonance to voice
- Frontal sinus:
  - Lightens bone, moistens inhaled air, and gives resonance to voice
- Maxillary sinus:
  - Lightens bone, moistens inhaled air, and gives resonance to voice
- Sphenoidal sinus:
  - Lightens bone, moistens inhaled air, and gives resonance to voice

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Description

Learn about the anatomy and landmarks of the skull, including the cranial and facial bones, sutures, and orbital and nasal complexes. Understand the structure and features of the paranasal sinuses.