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Skeletal System:
The Axial Skeleton
Skull
Vertebral Column
Ribs
Sternum
The Skull
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22 separate bones, many
fused together
Two divisions:
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Cranial Bones (8 bones)
Facial Bones (14 bones)
Bones of the Cranium
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Enclose and protect the
brain
Bones:
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Frontal (1)
Parietal (2)
Temporal (2)
Occipital (1)
Sphenoid (1)
Ethmoid (1)
Sphenoid
bone
Ethmoid
bone
Ethmoid and Sphenoid Bones
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Ethmoid Bone: anterior part of
the cranium base
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Forms the floor of the cranium
Makes up the medial wall of the orbits
(eye sockets)
The major supporting structure for
the nasal cavity and attachment for
the covering membranes of the brain.
Sphenoid Bone: medial base of
the skull
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Connects the frontal, temporal,
parietal and occipitial bones
Sella Turcica: a “saddle” for the
pituitary gland in the brain
Sutures in the Skull
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Suture: An immovable joint
found only in the skull bones
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Coronal Suture: between the
frontal and two parietals
Sagittal Suture: between the
two parietals
Lambdoid Suture: between
the two parietals and the
occipital
Squamous Sutures: between
the parietals and temporal
bones
Fontanels
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Membrane-filled spaces found
between cranium bones in
infants
“Soft Spots”
Eventually become ossified
(replaced by bone- 2 years)
Allow for:
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The babies skull to compress,
thus allowing childbirth
The brain to grow before the
skull is completely fused
Facial Bones
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Your face grows the most in the
first two years; then stops by the
age of 16.
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Nasal Bones
Maxilla: form the lower orbit and
upper jaw
Zygomatic Bones: cheekbones
Mandible: lower jawbone
Lacrimal Bones: smallest bones in
the face; have a foramen for the tear
duct to pass
Palatine Bones: form the hard palate
in the roof of the mouth
Hyoid Bone
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A U-shaped bone located
in the neck between the
mandible and the larynx
(voicebox)
Does not articulate with
any other bone
Supports the tongue
Provides attachment for
muscles to allow for neck
movement and
swallowing
Vertebral Column
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Protects the Spinal Cord
Allows the major nerves to
enter and exit the spinal
cord
Usually 33 Bones
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7 Cervical
12 Thoracic
5 Lumbar
5 Sacral (fused to form the
sacrum)
4 Coccygeal (fuse to form one
or two fused = coccyx)
Typical Vertebra
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Body: the thick weight bearing
portion
Vertebral foramen: the hole
that holds the spinal cord
Spinous Process: a single
projection for muscle
attachment
Transverse Process: two lateral
projections for muscle
attachment
Articular Processes: the facets
that allow the vertebrae to move
with the vertebrae superior and
inferior to them
Atlas and Axis
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Atlas (C1): supports the
head
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Articulates with the
occipital condyles of the
skull (nod your head
“yes”)
Axis (C2): The “peglike”
dens makes a pivot for
the head to rotate (move
your head “no”)
Sacrum and Coccyx
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Sacrum (holy bone): 5 fused
vertebrae
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Usually starts to fuse at age
16-18 and end in mid 20s)
Provides a foundation for the
pelvis and allows nerves to
pass
Coccyx: Usually 4 (can be
3-5) vertebrae that fuse
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Fusion occurs between 20-30
years of age
Epidural Anesthesia
Numbing medicine is delivered near the spinal cord
through the sacrum
Sternum
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Aka: Breastbone
Three separate bones:
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Manubrium
Body
Xiphoid Process
Articulates with the ribs,
provides attachment
point for some
abdominal muscles,
hematopoiesis
Fuses in late teens;
completely by age 40.
Ribs
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12 pairs (24 total)
True Ribs: pairs 1-7
directly attach to the
sternum by costal
cartilage
False Ribs: pairs 8-12,
their cartilage attaches to
the 7th rib cartilage
Floating Ribs: pairs 1112; don’t attach to the
sternum