Unit 4 (Cranium)
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give the total number of cranial bones and their names:
- 8 cranial bones:
- frontal bone
- parietal bones (2)
- temporal bones (2)
- occipital bone
- ethmoid bone
- sphenoid bone
how many bones of the entire skull are there?
- 8 cranial bones
- 14 facial bones (next unit)
- 22 bones of the skull in total
give the correct term for the "skull cap" and the bones it is comprised of:
- the Calvarium:
- frontal bone
- 2 parietal bones
- occipital bone
what is the name for the widest point of the skull?
while the inferior nasal conchae is a separate facial bone, the superior and medial nasal conchae are actually a part of which cranial bone?
What two bones make up the bony nasal septum?
- the upper part is the perpendicular plate of the ethmoid bone
- the lower part is the vomer
the brain and spinal cord are covered by three layers of _______ that adhere to the cranium by way of the _____________.
- meningeal grooves
on the interior surface of the cranium, the large grooves are the ___________ and the small grooves are the ___________.
- meningeal grooves
the joints of the cranium are of the ____________ type.
give the approximate ages at which each skull fontanel closes:
- posterior: 1 month
- anterior: 2 years
- sphenoids: 3 months
- mastoids: 2 years
describe the growth rate of the average cranium:
- grows rapidly until about 5-6 years of age
- then grows slowly until around 12 years
- (mostly reached its full size at that point)
irregular bones that sometimes form along the fontanels when they are closing:
give the dimensions of the labeled spans and three aspects to remember when considering these dimensions:
- A. 6 inches (15cm)
- B. 7 inches (18cm)
- C. 9 inches (22cm) - submentovertical aspect
- there is less atrophy in the skull than anywhere else in the body
- the skull is wider in the back than in the front (parietal area is widest point)
- internal structures are located in a different place if these measurements are off by more than an inch.
describe the petrous pyramids (4):
- part of the temporal bone
- densest part of cranium
- houses all internal ear structures
- used to measure pt's head to determine shape category
name the three common shapes of the skull:
- mesocephalic skull (average)
- brachycephalic skull (wider than average)
- dolichocephalic skull (narrower than average)
give some specifics about the mesocephalic skull:
- the most average
- petrous pyramids open to the back at a 47° angle to MSP
- add or subtract 7° to this angle for the other two skull shapes!!
give some specifics about the brachycephalic skull:
- the wider than average skull
- it is wider than it is from front to back
- it is shallow from vertex to base
- petrous pyramids open to the back at a 54° angle to MSP
give some specifics about the dolichocephalic skull:
- the more narrow than average skull
- long from front to back
- deep from vertex to base
- narrow from side to side
- internal structures are lower in reference to IOML
- petrous pyramids open to the back at a 40° angle to MSP
what represents the highest level of facial bone mass?
the supraorbital groove (SOG)
give a definition and several aspects of the frontal sinus:
- an air-filled cavity of the frontal bone located between the inner and outer table of the skull
- has one main septum, the inner sinus septum
- varies in shape and size in individuals
what bones does the frontal bone articulate with?
- parietal bones
- greater wing of sphenoid
- nasal bones
name three structures that the ethmoid bone helps to form:
- helps form part of the anterior cranial fossa (where the brain sits)
- helps form orbital cavity (ethmoid sinus directly between eyes)
- helps form nasal cavity (perpendicular plate)
what is the function of the foramina on top of the cribiform plate?
for passage of the olfactory nerves
crista galli is the attachment site for the:
- falx cerebri (the duramatter of the brain)
- (the membrane that divides cerebrum into right and left halves)
the posterior part of the sphenoid and basilar portion of the occipital:
the portion of the occipital bone that is anterior to the foramen magnum is the:
the jugular foramen is formed between which two bones?
- temporal bone
- occipital bone
the portion of the occipital bone that includes everything superior to the foramen magnum:
what do the condyles of the occipital bone and C1 form?
the occipito-atlantal joint
name the three main parts of the occipital bone:
- squamous portion
- basilar portion
what part of the sphenoid does the temporal bone articulate with?
which part of the cranial fossa does the temporal bone help to form?
- mainly the middle cranial fossa
- slightly with posterior cranial fossa
the zygomatic process of the temporal bone articulates with the ___________ (facial bone) to form the ____________.
a long, slender, pointed process that projects posteriorly to the mandible and anteriorly to the EAM:
the thickest, densest bone in the skull, used as an identifying landmark in radiographs for positioning of the skull:
petrous portion of temporal bone
zygomatic process is continuous with a ridge of bone called the:
______________ fits into the mandibular fossa of the temporal bone.
- condyle of mandible
- (forms the temporomandibular joint - TMJ)
the __________________ prevents the mandibular condyle from slipping too far forward from the mandibular fossa of the temporal bone.
the portion of the temporal bone that helps to form the EAM:
describe how the petrous portion of the temporal bone projects for different skull shapes:
- projects posteriorly 47° to mastoid and squamous portions in normal skull (mesocephalic)
- projects posteriorly 40° to mastoid and squamous portions in narrow skull (dolichocephalic)
- projects postiorly 54° to mastoid and squamous portions in wide skull (brachycephalic)
separates internal ear from the brain:
the first and largest air cell to develp in the mastoid:
a part of the middle ear that is covered by the tegman tympani:
where is the base of the temporal bone located?
- where the petrous portion joins with the squamous and mastoid portions
- (apex is tip of petrous portion)
the top of the temporal bone that is located externally at the TEA (top of ear attachment):
what are the bones of the cranium joined by?
how many areas of incomplete ossification are in newborns?
- sphenoidal (2)
- mastoid (2)
what two parts is the skull divided into?
name the two functions of the skull:
- protects the brain
- supports the face
what are the two plates of compact tissue separated by?
which plate of the skull is thicker?
the outer layer
how many regions is the cranial floor divided into?
name the major sutures of the skull:
- coronal: between frontal and parietals
- sagittal: between two parietals
- squamosal: between temporal and parietal
- lambdoidal: between occipital and parietals
name the sutural points:
- bregma: junctions of coronal and sagittal sutures
- lambda: juntion of lambdoidal and sagittal sutures
- pterion: junction of parietal, squamosal suture and sphenoid
- asterion: junction of occipital, parietal, mastoid portion of temporal
name the two main parts of the frontal bone:
- vertical (squamous) portion
- horizontal (orbital plates) portion
what are the orbital plates separated by?
what is located between the inner and outer table of the frontal bone?
what fits into the ethmoid notch?
- crista galli
- cribiform plate
describe the position of the ethmoid bone:
between the orbits
what are the two lateral masses of the ethmoid that hold aircells called?
what are the three main parts of the ethmoid?
- lateral masses
- vertical plate
- horizontal plate
what makes up the horizontal plate of the ethmoid?
the cribiform plate
what makes up the vertical plate of the ethmoid?
the perpendicular plate
what does the perpendicular plate articulate with?
how do the nasal conchae project and what do they divide?
- inferior from labyrinths
- divide nasal cavity
name the three nasal conchae and an alternate name for them:
- nasal turbinates
- superior, middle, and inferior
describe the classifications of the nasal conchae:
- the superior and middle conchae are part of the ethmoid bone
- the inferior concha is a separate facial bone
what the name of the area that is the widest measurement of the skull?
what bone is anterior to the temporal bones and anterior to the basilar portion of the occipital bone?
what contains the pituitary gland?
what does the sphenoid articulate with?
all other seven cranial bones
give another name for the sella turcica:
where on the sphenoid bone are the sphenoid sinuses located?
where is the pons of the brain situated within the cranium?
at the clivus
where do the optic nerves cross and pass through the optic canal?
list the three foramen of the sphenoid bone from anterior to posterior:
- foramen rotundum
- foramen ovale (largest)
- foramen spinosum (smallest)
allows blood to drain from the brain:
- jugular foramen
- (via jugular veins)
list the five portions of the temporal bone:
what is formed by the articulations of the condyle of the mandible and the mandibular fossa of the temporal bone?
tmj (tempomandibular joint)
what keeps the condyle of the mandible from slipping out of the fossa where it articulates with the temporal bone?
what is noticable about the mastoid tip when comparing genders?
the tip is generally larger in males
what is the external landmark used to locate the petrous ridge?
the TEA (top of ear attachment)
name the structures located in the middle ear:
- ear drum
- tympanic cavity
name the structures located in the internal ear:
- cochlea vestibule
- semicircular canals
for the lateral skull projection, what should be done for a hypersthenic patient?
place support under the head
for the lateral skull projection, what should be done for a hyposthenic or asthenic patient?
place support under thorax/chest
for the AP skull projection, a support may be needed under the head for what body habitus?
if you want to view the sella turcica, where would you center?
- lateral projection centered to 3/4" anterior and 3/4" superior to EAM
- (with the IOML aligned)
what is demonstrated on a dorsal decubitus projection of the skull?
sphenoid effusion (a major indicator of fracture at base of skull)
where are the petrous pyramids located in a PA projection of the skull vs. a PA axial projection?
- PA: in the orbits
- PA axial: in bottom 1/3 of orbits
what is the name of the projection used to view the occipital bone?
- townes/grashey method
- haas method
what is seen in the foramen magnum in the townes projection?
- the posterior clinoid processes
- dorsum sellae
describe the positioning for the Haas Method?
- 25degrees cephalic (PA)
- centered to 1.5" below inion
- CR exits 1.5" superior to nasion
- also called reverse townes
what bone is of primary interest for the townes and haas methods?
what are the three other names for the submentovertical projection of the skull?
- schuller method
- basal projection
what do the pterygoid processes help to form?
what is located between the zygoma and the greater wing of the sphenoid?
inferior orbital fissure
what is located between the greater and lesser wings of the sphenoid?
superior orbital fissure
how many sphenoid sinuses are there?
where the eustacian tube connects the middle ear to the nasopharynx:
- tympanic cavity
- (helps to equalize pressure)
what projection(s) best demonstrate the crista galli?
describe and name the reverse SMV projection:
- chin down on table/IR surface
- shoot down through vertex
- called the VSM
what projection best demonstrates the foramen rotundum?
what projection best demonstrates the foramen spinosum and ovale?
what projection best demonstrates the optic foramen?
what projection best demonstrates a sphenoidal effusion?
- upright lateral
- dorsal decubitus
what is seen on the lateral projection of the skull?
every bone of the skull
what projection best demonstrates the frontal bone?
in which projection do the orbits appear enlarged?
AP (they're further away)
what projection best demonstrates the base of the skull?
what do you do if the pt cannot duck the chin enough to use the OML for the townes method?
use the IOML with a 37° angle (increased angle by 7°)
name two projections that will cause the petrous pyramids to appear above the orbits:
- AP with caudal angle
- PA with cephalic angle
what projection best demonstrates the posterior ethmoid?
what projection best demonstrates the anterior ethmoid?
PA axial (Caldwell)
an opening into the apex of the petrous portion is for the:
- carotid canal
- (runs alongside the body of the sphenoid bone)
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