Chapter 7: The Axial Skeleton * The Ribs Figure 7 23

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Chapter 7The Axial Skeleton
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Human Skeleton

• Human Skeleton 206 Bones
• Axial Skeleton
• -longitudinal axis
• -80 bones
• Appendicular Skeleton
• -limbs
• -126 bones

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The Axial Skeleton
Figure 71a
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Axial Skeleton
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Appendicular Skeleton
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Axial Skeleton Function

• Support and protect organs in dorsal and ventral
  body cavities
• Provide surface area for muscle attachment
• Adjust position of head, neck, trunk
• Perform respiratory movements
• 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

Figure 710a
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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
Figure 710b,c
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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
Figure 711
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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
Figure 712a,b
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The Hyoid Bone

• Function
• Supports the larynx
• Attaches muscles of the larynx, pharynx, and
  tongue

Figure 712c
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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
• Lambdoid
• - separates occipital bone from parietal bones
• Corona
• - separates frontal bone from parietal bones
• Sagittal
• - separates parietal bones
• Squamous
• - (2) separates temporal bone from parietal bone

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Sutures

• The immovable joints of the skull

Figure 73a, b
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Sutures
Figure 73c
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Sutures
Figure 73d, e
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The Orbital Complex

• Portions of 7 cranial and facial bones

Figure 713
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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

Figure 714
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The Nasal Complex Sinuses

• Sinuses
• air filled chambers inside flat bones
• Function
• Reduce weight of bone
• 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

• Craniostenosis
• Premature closure of frontanels,
• Without surgery, the brain is crushed
• 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?

• 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?

• 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?

• 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

Figure 716
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The Vertebrae
Figure 720a
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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

• 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

• Kyphosis
• - exaggerated thoracic curvature
• Lordosis
• - exaggerated lumber curvature
• 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
Figure 717a,b
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The Vertebral Canal
Figure 717d,e
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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?

• Vertebrae are absorbed as adult stature is
  reached.
• Newborns require more support in the cervical
  region.
• The sacrum and coccyx fuse post-puberty.
• Vertebrae are formed that later become ribs.

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What is the importance of the secondary curves of
the spine?

• balances weight of head
• balances weight on lower limbs
• allows walking
• provides greater flexibility

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When you run your finger along a persons spine,
what part of the vertebrae are you feeling just
beneath the skin?

• 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?

• second cervical vertebra posterior neck
• first cervical vertebra posterior neck
• occipital bone posterior base of skull
• 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?

• thoracic
• lumbar
• sacral
• cervical

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Why are the bodies of the lumbar vertebrae so
large?

• They develop first and therefore have longer to
  grow.
• To provide more flexibility.
• To distribute weight over a larger area.
• 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

Figure 722a
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Articulations of Ribs and Vertebrae
Figure 722b
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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
Figure 723
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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 sternum

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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?

• True ribs attach directly to the sternum by their
  own costal cartilage.
• True ribs are entirely bony.
• False ribs are not part of the thoracic cage.
• 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)?

• 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?

• Vertebrosternal ribs attach to the sternum.
• Vertebrochondral ribs attach to costal cartilage.
• Vertebrosternal ribs increase in curvature and
  length from 1 - 7.
• All of the above are true.