Download The Axial Skeleton

The Axial Skeleton
Axial Skeleton
• the skull is actually several bones that
come together as an embryo develops
• the cranial bones protect the brain, ears
and eyes
• some cranial bones provide attachment
points for muscle → movement of head,
jaw, and neck
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• the cranial bones are divided into the
calvaria and the cranial base
calvaria = frontal, occipital, parietal,
temporal
cranial base = ethmoid, sphenoid
• the rest of the skull is made of 14 facial
bones
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• several of the bones of the skull contain
sinuses = cavities lined with ciliated
epithelial cells that secrete mucous
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• the left and right frontal sinuses are
posterior to the frontal bone
– not present at birth
– begin development from age 2 to 5
– fully develop in the late teens
– function: lighten skull, warm air
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the frontal bone
• forms the forehead and eyebrow ridges
• flat vertical = forehead
• lower concave = orbits (
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comparative anatomy note:
• males have a thicker orbital ridge
than females
• the eyebrows of a male sit lower
on the orbital ridge
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the temporal bone
• complex shape
• distinct features
noteworthy features of the temporal
bones:
– mastoid process
– styloid process
– tympanic region
– zygomatic process
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mastoid process
• attachment of neck muscles
• complex of cavities = mastoid sinuses
– mastoid sinuses connected to inner ear
– vulnerable to bacterial infection that affects
ears and throat
– adjust inne ear to pressure changes
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styloid process
• varies in length from individual to
individual
• important attachment point for muscles
and tendons of the neck and throat
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tympanic region
• houses the internal components of the
ears; includes the 3 small bones of the
malleus (
incus (
stapes (
these bones develop from the facial bones
in an embryo
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zygomatic process
• forms the zygomatic arch with the
zygomatic bone (facial)
• forms the cheek
• attachment for muscles used in chewing
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The parietal bone
• forms the top, side, and posterior portion
of the cranium
• protects the posterior portion of the brain
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The occipital bone
• forms the posterior base of the cranial
vault
• series of bones fused together in an
embryo
• an opening is left = foramen magnum or
occipital foramen
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The occipital bone
• the spinal cord enters through the occipital
foramen
• occipital condyles provide attachment of
the head to the vertebral column, allow
head movement
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The sphenoid bone
• in contact with almost all other skull bones
• helps form facial features
• contains sphenoidal sinuses
– connected to, and help form nasal cavities
• major blood vessels and nerves of the
eyes and face pass through the sphenoid
• forma a structure, sella turica, which
protects the pituitary gland
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The ethmoid bone
• passageway for the nerves that detect
smell
• contains the ethmoid labyrinth
– cleans and moistens air that enters the nose
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Most of a person’s facial features are
determined by the
1) mandible
2) maxillary bones
3) zygomatic bones
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zygomatic bones
• zygomatic arch
maxillary bones
• upper jaw
• larger facial bones
• form area around nose (lateral surfaces)
• area under eyes (medial border of orbits)
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maxillary bones
• passageway for major blood vessels and
nerves = inferior orbital foramen
• teeth develop on the lower surface
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palatine bones
• between the maxillary and sphenoid bones
• help form the
1) the walls of the nasal cavity
2) the roof of the mouth
3) the bottom of the orbits
• this bone pair grows in height as facial
features mature
birth → adolescence
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mandible
• largest facial bone
• body of the mandible contains teeth
• condyle of the mandible articulates with
the temporal bones
• contains passageways for blood vessels
and nerves to the the chin and lower lip =
mental foramen
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mandible
• only skull bone not fused to other bones of
the skull (ear bones, hyoid)
hyoid bone
• horshoe-shaped bone
• suspended below mandible by muscles
• anchors muscles of the neck
• attaches to muscles of the tongue
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teeth
• bones that grow out of an alveolus in the
mandible or maxilla
• has a crown – projects above the gum
• has a root – embedded in the alveolus
• a hard enamel covers the crown
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The remainder of the facial bones are tiny
bones:
nasal, lacrimal, vomer
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The vertebral column and ribs
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vertebral column
region
#
association/articulation
cervical
7
neck
thoracic
12
rib cage
lumbar
5
lower back
sacral
5*
hip bones
coccygeal
3 - 5*
tail end
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most vertebrae have a
• vertebral body
• vertebral arch
• vertebral foramen
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vertebral body
• supports weight of body
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vertebral arch
• dorsal to the body
• has several features
– pedicles (2)
– articular processes (4)
– transverse processes (2) – lateral
– spinous process
• processes provide muscle attachment =
movement of appendages, head, neck,
vertebral column
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vertebral foramen
• passageway for spinal cord
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cervical
• smaller body
• small transverse processes
• short, bifurcated* spinous process
unique feature:
2 transverse foramina for major blood
vessels to the skull
cervical 1 & 2 = atlas and axis
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atlas
• supports the skull
• lacks a body
• large articular surfaces attach to the
occipital bone
axis
• large protrusion = dens (odontoid
process) → rotation and free movement
of the atlas and skull
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thoracic
• larger body
• long, narrow spinous process
unique features:
each transverse process (2) has a facet
for articulation with a rib
another facet is located on the dorsal
portion of the body
→ articulation that allows the ribs to flex
during breathing
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lumbar
• largest
• thickest
• support most of the body’s weight
• anchor the back muscles = balance while
moving, sitting, or standing
• short stubby spinous process → bend
backward
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sacral
• form the sacrum
• have large, lateral articular surfaces =
fuse with hip bone
• in females:
sacrum is
shorter
wider
less curved
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In most individuals the vertebral arch is
not present on the last 2 vertebra = sacral
canal
The spinal cavity is exposed in the sacral
canal
The spinal cord ends in the lumbar region
Result =
opportunity to collect spinal fluid with
minimal risk of nerve damage
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coccygeal
• coccyx (tailbone)
• no foramen
• muscle attachment of upper leg muscles
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The rib cage consists of:
costal cartilage
ribs
sternum
• serves as a protective structure
• assists in breathing
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normally 12 ribs, but . . .
some individuals develop small cervicacl
and lumbar ribs
Why?
Scientists have discovered that each
vertebra has the genetical potential to
become a rib
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7 upper ribs = true ribs
• attach directly to the sternum by costal
cartilage
ribs 8, 9, & 10 = false ribs
• attached by costal cartilage to the rib
above
last 2 ribs = floating ribs
• not attached ventrally
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The sternum serves as:
• an articulation with the clavicles
• an articulatioin with ribs 1 – 7
• an attachment for the chest and shoulder
muscles
• an attachment for the stomach muscles
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