Download Chapter 7: The Axial Skeleton

Chapter 7:
The Axial Skeleton
1
Human Skeleton
• Human Skeleton = 206 Bones
1. Axial Skeleton:
-longitudinal axis
-80 bones
2. Appendicular Skeleton:
-limbs
-126 bones
2
The Axial Skeleton
3
Figure 7–1a
Axial Skeleton
4
Appendicular Skeleton
5
Axial Skeleton Function
1. Support and protect organs in dorsal
and ventral body cavities
2. Provide surface area for muscle
attachment:
A. Adjust position of head, neck, & trunk
B. Perform respiratory movements
C. Stabilize appendicular skeleton
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Bones of the Axial Skeleton
• The skull: 22 bones
– 8 cranial bones:
• form the braincase or cranium
– 14 facial bones:
• protect and support entrances to digestive and
respiratory tracts
• Skull bones interconnect at immovable
joints called sutures
– Dense fibrous CT
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Skull: 22 Bones
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Cranial Bones
• Enclose the cranial cavity
• Which contains the brain:
– and its fluids, blood vessels, nerves, and
membranes
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The Facial Bones
• Superficial facial bones:
– for muscle attachment
– Maxillary, Lacrimal, Nasal, Zygomatic, and
Mandible
• Deep facial bones:
– separate the oral and nasal cavities
– form the nasal septum
– Palatine bones, Inferior nasal conchae, and
Vomer
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The Maxillary Bones
• The largest facial bones
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Figure 7–10a
Functions of the Maxillary Bones
•
•
•
•
•
Support upper teeth
Form inferior orbital rim
Form lateral margins of external nares
Form upper jaw and hard palate
Contain maxillary sinuses (largest
sinuses)
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The Palatine Bones
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Figure 7–10b,c
Functions of the Palatine Bones
• Form the posterior portion of the hard
palate
• Contribute to the floors of the orbits
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The structures and functions
of the nasal complex.
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The Small Bones of the Face
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Figure 7–11
Functions of the Nasal Bones
• Nasal Bones
– Support the bridge of the nose
– Connect to cartilages of the distal part of the nose
(external nares)
• Vomer
– Forms the inferior portion of the bony nasal septum
• Inferior Nasal Conchae
– To create air turbulence in the nasal cavity
– To increase the epithelial surface area
– To warm and humidify inhaled air
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The Mandible
Forms the lower jaw
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Figure 7–12a,b
The Hyoid Bone
• Function:
– Supports the larynx
– Attaches muscles of the
larynx, pharynx, and
tongue
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Figure 7–12c
Marks of the Hyoid Bone
• Greater horns (greater cornua):
– support larynx
– attach muscles of the tongue
• Lesser horns (lesser cornua):
– attach stylohyoid ligaments
– support hyoid and larynx
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Skull
• Four major sutures:
1. Lambdoid:
- separates occipital bone from parietal bones
2. Corona:
- separates frontal bone from parietal bones
3. Sagittal:
- separates parietal bones
4. Squamous:
- (2) separates temporal bone from parietal bone
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Sutures
• The immovable joints of the skull
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Figure 7–3a, b
Sutures
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Figure 7–3c
Sutures
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Figure 7–3d, e
The Orbital Complex
• Portions of 7 cranial and facial bones
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Figure 7–13
The Orbital Complex
• Forms the eye sockets (orbits):
– frontal bone (roof)
– maxillary bone (floor)
– maxillary, lacrimal and ethmoid bones
(orbital rim and medial wall)
– sphenoid and palatine bones
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The Nasal Complex
• Bones of the nasal cavities and paranasal
sinuses
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Figure 7–14
The Nasal Complex: Sinuses
• Sinuses:
–
–
air filled chambers inside flat bones
Function:
1. Reduce weight of bone
2. House mucus membranes that moisten and clean
incoming air
-
Found in:
-
Sphenoid, ethmoid, frontal, palatine, and maxillary
bones
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The differences between the
skulls of infants, children, and
adults.
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Skull Development
• Intramembranous ossification from many centers of
ossification
• During development:
– brain grows more rapidly than cranial bones
• Growing skull bones are held together by bands of
fibrous CT to provide flexibility
– Expansion of brain, compression for birth
• Large intersections of CT between the bones =
fontalels (“soft spots”)
– Persist until age 5
• Around age 5:
– Brain stops growing in size, solid sutures form between
cranial bones
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The Infant Skull
• Fusion is not complete at birth:
– 2 frontal bones
– 4 occipital bones
– several sphenoid and temporal elements
• Fontanels
– Are areas of fibrous connective tissue (soft
spots)
– Cover unfused sutures in the infant skull
– Allow the skull to flex during birth
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The 4 Fontanels
• Anterior fontanel:
– frontal, sagittal, and coronal sutures
• Occipital fontanel:
– lambdoid and sagittal sutures
• Sphenoidal fontanels:
– squamous and coronal sutures
• Mastoid fontanel:
– squamous and lambdoid sutures
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Infant Skull
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Skull Development Abnormalities
1. Craniostenosis:
-
Premature closure of frontanels,
Without surgery, the brain is crushed
2. Microcephaly:
- Brain fails to enlarge
- Cranium remains small
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Craniostenosis
Microcephaly
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In which bone is the foramen magnum
located?
A.
B.
C.
D.
sphenoid
occipital bone
ethmoid
parietal bone
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Tomás suffers a blow to the skull that
fractures the right superior lateral
surface of his cranium. Which bone is
fractured?
A.
B.
C.
D.
frontal bone
right temporal bone
right parietal bone
ethmoid
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Which bone contains the depression
called the sella turcica? What is located
in this depression?
A.
B.
C.
D.
sphenoid bone; pituitary gland
ethmoid; olfactory epithelium
temporal bone; inner ear
lacrimal bone; tear apparatus
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The vertebral regions, the
curvatures of the vertebral
column, and their functions.
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The Vertebral Column: 26 Bones
• The spine or vertebral column:
– protects the spinal cord
– supports the head and body
•
•
•
•
•
7 cervical vertebrae (C1-C7)
12 Thoracic vertebrae (T1-T12)
5 Lumbar vertebrae (L1-L5)
1 Sacrum (5 fused)
1 Coccyx (3-5 fused)
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Regions and Curves of the
Vertebral Column
• 26 bones:
– 24 vertebrae, the sacrum,
and coccyx
• Vertebral column is not
straight
– 4 curves bring the weight
of the body in line with
the central axis
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Figure 7–16
The Vertebrae
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Figure 7–20a
Comparing Vertebrae
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Characteristics of the Sacrum
and Coccyx
• The sacrum:
– is curved, more in males than in females
– protects reproductive, urinary, and
digestive organs
• The coccyx:
– attaches ligaments and a constricting
muscle of the anus
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4 Curvatures of the
Vertebral Column
1.
2.
3.
4.
Cervical curve
Thoracic curve
Lumbar curve
Sacral curve
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Primary Curves
• Thoracic and sacral curves:
– are called primary curves (present during
fetal development)
– or accommodation curves (accommodate
internal organs)
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Secondary Curves
• Lumbar and cervical curves:
– are called secondary curves (appear after
birth in first year of life)
– or compensation curves (shift body weight
for upright posture)
– Necessary for bipedalism
– Cervical: holds head up
– Lumbar: standing
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Abnormalities in Curvature
1. Kyphosis:
- exaggerated thoracic curvature
2. Lordosis:
- exaggerated lumber curvature
3. Scoliosis:
- abnormal lateral curvature
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Construction of Column
• Vertebral body: stacking
– transfers weight along the spine
• Intervertebral disc:
– Spacing between bodies (not C1
and C2)
– Annulus Fibrosus: Outside
• Fibrocartilage
– Nucleus pulposus: Inside
• Gel (cushion)
• Absorbs Shock
– Loss of water from discs =
shrinking height
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Construction of Column
• Elastic ligaments:
– link bodies for alignment
• Intervertebral foramen:
– holes formed by spacing from discs, allow spinal nerves
to exit column
• Vertebral arch:
– Bone attached to vertebral body, with body it forms
vertebral foramen
• Vertebral Foramen:
– Hole for spinal cord
• Vertebral Canal:
– Bony canal for spinal cord
– Formed by stacking of vertebral foramen
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Structure of a Vertebra
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Figure 7–17a,b
The Vertebral Canal
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Figure 7–17d,e
Spina bifida
• Vertebral arch fails to develop
correctly at 3 weeks (fetus) and the
spinal cord is unprotected or even
exposed
• 4/1000 births show some degree
– Due to lack of folic acid
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Why does the vertebral column of an
adult have fewer vertebrae than that
of a newborn?
A. Vertebrae are absorbed as adult
stature is reached.
B. Newborns require more support in the
cervical region.
C. The sacrum and coccyx fuse postpuberty.
D. Vertebrae are formed that later
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become ribs.
What is the importance of the
secondary curves of the spine?
A.
B.
C.
D.
balances weight of head
balances weight on lower limbs
allows walking
provides greater flexibility
55
When you run your finger along a person’s
spine, what part of the vertebrae are you
feeling just beneath the skin?
A.
B.
C.
D.
superior articular processes
pedicles
transverse processes
spinous processes
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Joe suffered a hairline fracture at the
base of the dens. Which bone is
fractured, and where is it located?
A. second cervical vertebra;
posterior neck
B. first cervical vertebra; posterior
neck
C. occipital bone; posterior base of
skull
D. sacrum; posterior pelvis
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Examining a human vertebra, you notice that, in addition
to the large foramen for the spinal cord, two smaller
foramina are on either side of the bone in the region of
the transverse processes. From which region of the
vertebral column is this vertebra?
A.
B.
C.
D.
thoracic
lumbar
sacral
cervical
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Why are the bodies of the lumbar
vertebrae so large?
A. They develop first and therefore
have longer to grow.
B. To provide more flexibility.
C. To distribute weight over a larger
area.
D. To provide greater protection to
the lumbar spinal nerves.
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The significance of
articulations between ribs,
thoracic vertebrae, and
sternum.
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The Thoracic Cage
• The skeleton of the chest:
– supports the thoracic cavity
• Consists of:
– 24 Ribs
– 1 sternum (breastbone)
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The Sternum
• The sternum:
– a flat bone
– in the midline of the thoracic wall
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The Rib Cage
• Formed of ribs and sternum
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Figure 7–22a
Articulations of Ribs and
Vertebrae
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Figure 7–22b
Functions of the Thoracic Cage
• Protects organs of the thoracic cavity:
– heart, lungs, and thymus
• Attaches muscles:
–
–
–
–
for respiration
of the vertebral column
of the pectoral girdle
of the upper limbs
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The Ribs
66
Figure 7–23
Functions of Ribs
• Ribs:
– are flexible
– are mobile
– can absorb shock
• Rib movements (breathing):
– affect width and depth of thoracic cage
– changing its volume
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Ribs
• Ribs (costae):
– are 12 pairs of long, curved, flat bones
– extending from the thoracic vertebrae
• Ribs are divided into 3 types:
1. 7 pairs of true ribs:
• Separate cartilage to attach to sternum
2. 3 pairs of false ribs:
• Common shared cartilage to attach to sternum
3. 2 pairs of floating ribs:
- no cartilage, no attachment to sternum68
KEY CONCEPT
• The axial skeleton:
– protects the brain, spinal cord, and
visceral organs of the chest
• Vertebrae:
– conduct body weight to the lower limbs
• Lower vertebrae are larger and
stronger:
– because they bear more weight
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How could you distinguish between
true ribs and false ribs?
A. True ribs attach directly to the
sternum by their own costal
cartilage.
B. True ribs are entirely bony.
C. False ribs are not part of the
thoracic cage.
D. True ribs are attached only to the
sternum.
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Improper administration of
cardiopulmonary resuscitation (CPR)
can result in a fracture of which
bone(s)?
A.
B.
C.
D.
cervical vertebra and ribs
thoracic vertebra and ribs
sternum and thoracic vertebra
sternum and ribs
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What are the main differences between
vertebrosternal and vertebrochondral
ribs?
A. Vertebrosternal ribs attach to the
sternum.
B. Vertebrochondral ribs attach to
costal cartilage.
C. Vertebrosternal ribs increase in
curvature and length from 1 - 7.
D. All of the above are true.
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