Chapter 11 Skull & Cranial Bones (Lesson 1)
What is the squamous portion of the occipital bone?
rounded part of the external surface of the occipital bone, forms most of the back of the head; located superior to the external occipital protuberance.
What articulations form the Atlanto-Occipital joint?
skull & cervical spine
What is the styloid process?
slender bony projection that projects inferior to the mandible and anterior to the EAM.
The left temporal bone is situated between...
the greater wing of the sphenoid bone anteriorly & occipital bone posteriorly
What is the thickest and densest bone bone in the cranium?
the petrous portion of the temporal bones
What is the supraorbital groove (SOG) (squamous portion of frontal bone)?
the slight depression above each eyebrow; corresponds to floor of anterior fossa of the cranial vault (at level of orbital plate or highest level of facial bone mass)
What is the TEA?
top of the ear attachment, important external landmark corresponds with the level of the petrous ridge of the petrous pyramids.
What cranial bones does the ethmoid bone articulate with?
(1) Frontal (2) Sphenoid
What 4 processes correspond to the legs of the imaginary (sphenoid) bat?
(1) Lateral Pterygoid Processes (plates)- more lateral, flat extensions (2) 2 Medial Pterygoid Process (plates) - medial to the lateral processes and end inferiorly in small hooklike processes called Pterygoid hamuli.
What are the articulations of the occipital bone?
(1) Right Parietal (2) Left Parietal (3) Right temporal (4) Left temporal (5) Sphenoid (6) Atlas (1st cervical vertebra)
What are the 3 primary parts of the temporal bones (front cutaway view)?
(1) Squamous Portion - thin upper portion that forms part of the wall of the skull. (2) Mastoid Portion - area posterior to EAM with a prominent mastoid process or tip (3) Petrous Portion (petrous pyramid or pars petrosa) - pyramid-shaped portion that houses the organs of hearing and equilibrium, including mastoid air cells; sometimes called petromastoid portion due to it internally including the mastoid portion.
What are the 3 pairs of small openings or foramina located in the greater wings of the sphenoid bone?
(1)Foramen rotundum & (2)Foramen ovale - both are small openings on superior & oblique views (3) Foramen spinosum
Superior View of Sphenoid Bone:
*Centrally located cranial bone that forms the anchor for all 8 cranial bones
What are the 2 main parts of the frontal bone?
1) Squamous (vertical portion) - forms the forehead 2) Orbital (horizontal portion) - forms superior part of orbit
What 4 bones make up the calvarium (skull cap)?
1. Frontal 2. Right parietal 3. Left parietal 4. Occipital
What does the squamous/vertical portion of the frontal bone consist of?
1. Glabella 2. Supraorbital groove (SOG) 3. Supraorbital margin (SOM) 4. Supraorbital notch (foramen) 5. Frontal tuberosity (eminence)
What does the orbital/horizontal portion of the frontal bone consist of?
1. SOMs 2. Superciliary ridges 3. Glabella 4. Frontal tuberosities
How many facial bones are there?
14
What are the 2 lateral labyrinths (masses)?
2 Lateral masses, suspended from undersurface of cribriform plate on each side of perpendicular plate, containing ethmoid air cells/sinuses, helps to form the medial walls of orbits and lateral walls of nasal cavity.
How many pairs of wings does the sphenoid bone contain?
2 pairs, Lesser & Greater wings: (1) Lesser Wings - triangular & nearly horizontal, ending medially in the 2 anterior clinoid processes - project laterally from the superoanterior portion of the body & extend to about the middle of each orbit. (2) Greater Wings - extend laterally from the sides of the body and form a portion of the floor of the & sides of the cranium.
Each of the temporal bones articulate with what bones?
3 cranial bones: (1) Parietal (2) Occipital (3) Sphenoid
What are the articulations of the frontal bone?
4 articulations with 4 cranial bones: (1) Right parietal (2) Left Parietal (3) Sphenoid (4) Ethmoid
How many cranial bones does the frontal bone articulate with?
4 cranial bones: 1) Right Parietal 2) Left Parietal 3) Sphenoid 4) Ethmoid
How many cranial bones do the parietal bones articulate with?
5 cranial bones: 1) Frontal 2) Occipital 3) Temporal 4) Sphenoid 5) Opposite parietal
What 4 bones make up the floor of the cranium?
5. Right temporal 6. Left temporal 7. Sphenoid 8. Ethmoid
What bones does the occipital bone articulate with?
6 bones: 1) Right parietal 2) Left parietal 3) Right temporal 4) Left temporal 5) Sphenoid 6) Atlas (1st cervical vertebra)
The cranium consists of how many bones?
8 - divided into the calvarium (skullcap) and the floor (each consist of 4 bones)
The external occipital protuberance (inion) is....
A bony prominence on the outer surface which can be easily palpated (at the inferoposterior portion of the skull)
Name the anatomic structure: 2 bony projections arising from the posterior aspect of the lesser wings.
Anterior clinoid processes, larger & spread farther apart than posterior clinoid processes.
What is the 2-part articulation between the skull and the cervical spine?
Atlanto-occipital joints
Name this anatomic landmark: central portion that lies in the midline of the floor of the cranium (contains sphenoid sinus).
Body of Sphenoid
What is the external occipital protuberance (inion)?
Bony prominence on the outer surface which can be palpated (at the inferoposterior portion of the skull)
What modalities are useful for detecting deformities of the sella turcica?
CT & MRI
Name this anatomic structure: groovelike canals through which the optic nerve & certain arteries pass into the orbital cavity.
Chiasmatic or optic groove - lead on each side to an optic canal, which ends at the optic foramen (opening into the orbit)
Name this anatomic landmark: shallow depression that begins on the posteroinferior aspect of the dorsum sellae (sphenoid bone) & extends posteriorly to the foramen magnum at the base of the occipital bone.
Clivus - serves as base of support for pons & basilar artery
Describe this anatomic structure: small upper horizontal portion, containing many small openings or foramina where olfactory nerves pass (smell).
Cribiform plate
Describe this anatomic structure: projects superiorly from cribriform plate.
Crista Galli - derived from "rooster comb"
What anatomic feature is referred to as the "back of the saddle"?
Dorsum Sellae - posterior to sella turcica
What are the articulations of the parietal bones?
Each articulate with 5 cranial bones: (1) Frontal (2) Occipital (3) Temporal (4) Sphenoid (5) Opposite parietal
What anatomical feature separates each orbital plate from the other?
Ethmoid notch (the ethmoid bone fits into this notch)
What anatomy is located below the orbital plate?
Facial bones
What is the name of the large opening at the base of the occipital bone through which the spinal cord passes as it leaves the brain?
Foramen Magnum ("great hole")
What is the temporomandibular (TM) fossa?
Fossa located inferior to the zygomatic processes and just anterior to the external acoustic (auditory) meatus (EAM)
What is the most readily visible bone of the calvarium when viewed from the front?
Frontal bone (contributes to the formation of the forehead and superior part of each orbit)
What is the frontal tuberosity (eminence) (squamous portion of frontal bone)?
Larger rounded prominence on each side of the squamous portion of the frontal bone above the SOG
What projection best demonstrated the dorsum sellae?
Lateral skull
What projection best demonstrates the Sella Turcica?
Lateral skull
What is the name of the single bone that forms the inferoposterior portion of the calvarium (skullcap)?
Occipital bone
What single bone forms the inferoposterior portion of the calvarium (skullcap)?
Occipital bone
Name this anatomical landmark: 2 lateral condylar portions, oval processes with convex surfaces (located on either side of the foramen magnum).
Occipital condyles; articulate with depressions on the atlas (1st cervical vertebrae)
What bones make up the majority of the calvarium (skull cap)?
Parietal bones (paired - R & L)
What anatomical feature(s) is situated at the widest portion of the skull, and is located between the 2 parietal bones?
Parietal tubercles (eminences)
What is the widest portion of the skull located between the level of the 2 parietal bones?
Parietal tubercles (eminences)
Describe this anatomic structure: plate projecting midline downward from the ethmoid bone, and helps to form the bony nasal septum.
Perpendicular plate
What cranial bones make up the majority of the calvarium (skull cap)?
Right and Left Parietal bones; form the lateral walls of cranium & part of the roof
Name this anatomic landmark: central depression on the body that resembles a "saddle" from the side (means "Turkish saddle").
Sella Turcica - protects the pituitary gland (hypophysis cerebri)
What is the glabella (squamous portion of frontal bone)?
Smooth, raised prominence between the eyebrows just above the bridge of the nose
What cranial bone articulates with all other cranial bones?
Sphenoid bone (because of its central location)
What is the most vulnerable portion of skull, that usually is susceptible to fractures?
Squamous portion of the temporal bones
Name these anatomic structure(s): scroll-shaped projections of bone extending medially & downward from the medial wall of each labyrinth.
Superior & middle nasal conchae (turbinates)
Name this anatomic structure: irregularly shaped openings that provides added communication with orbits for numerous cranial nerves & blood vessels.
Superior orbital fissures
What anatomy is located above the orbital plate?
The anterior part of floor of the brain case
What is the vertex of the cranium?
The most superior aspect of the skull located near the center of the sagittal suture.
What is the squamous portion of the occipital bone?
The rounded part of external surface of occipital bone, forming most of the back of the head; located superior to the external occipital protuberance
What is supraorbital margin (SOM) (squamous portion of frontal bone)?
The superior rim of each orbit
What is the petrous ridge (petrous apex)?
The upper border or ridge of the petrous pyramids
T/F: Deformities of the sella are often the only clue that a lesion exists intracranially on radiograph.
True
Describe this anatomical feature: arch of bone extending from the squamous portion of the temporal bone.
Zygomatic process; meets the temporal process of zygomatic bone to form the zygomatic arch
What is the supraorbital notch (foramen) (squamous portion of frontal bone)?
a small hole or opening within the SOM slightly medial to its midpoint (supraorbital nerve & artery pass through it)
What is located above the orbital plate?
anterior part of the floor of the brain case
The sphenoid bone is shaped like a..
bat with its wings & legs extended as in flight
Where does the ethmoid bone primarily lie?
below the floor of the cranium
What are housed within the temporal bones?
delicate organs of hearing and balance
What is located below the orbital plate?
facial bones
Where are the temporal bones located?
in the floor of the cranium
What is the foramen magnum ("great hole")?
large opening located at the base of the occipital bone through which the spinal cord passes as it leaves the brain
The orbital plate is located...
on each side, forming the superior part of each orbit
What is the internal acoustic meatus?
opening or orifice that serves to transmit the nerves of hearing & equilibrium. (located near the center of the petrous pyramid on the posterior surface just superior to the jugular foramen)
What are the occipital condyles?
oval processes with convex surfaces, located on each side of the foramen magnum; articulates with depressions on the atlas (1st cervical vertebra)
