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Chapter 7
The Skeleton
Part B
Shilla Chakrabarty, Ph.D.
Copyright © 2010 Pearson Education, Inc.
Vertebral Column
• Transmits weight of trunk to lower limbs
• Surrounds and protects spinal cord
• Flexible curved structure containing 26 irregular bones
(vertebrae)
 Cervical vertebrae (7)—vertebrae of the neck
 Thoracic vertebrae (12)—vertebrae of the thoracic
cage
 Lumbar vertebrae (5)—vertebra of the lower back
 Sacrum—bone inferior to the lumbar vertebrae
 Coccyx—terminus of vertebral column
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Vertebral Column: Curvatures
C1
Cervical curvature
(concave)
7 vertebrae, C1–C7
Spinous
process
Transverse
processes
Thoracic
curvature
(convex)
12 vertebrae,
T1–T12
Intervertebral
discs
Intervertebral
foramen
Lumbar curvature
(concave)
5 vertebrae, L1–L5
Sacral curvature
(convex)
5 fused vertebrae
sacrum
Anterior view
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Coccyx
4 fused vertebrae
Right lateral view
Increase the resilience and
flexibility of the spine
Two posteriorly concave
curvatures:
Cervical and lumbar
Two posteriorly convex
curvatures:
Thoracic and sacral
Abnormal spine curvatures
Scoliosis (abnormal lateral
curve)
Kyphosis (hunchback)
Lordosis (swayback)
NOTE: The vertebrae become progressively
larger from cervical to lumbar region as they
have to support more weight
Ligaments
• Strap-like ligaments and trunk muscles hold the vertebral column in place and keep it upright
• Anterior and posterior longitudinal ligaments:
 Major supporting ligaments
 Run as continuous bands down the front and back surfaces of vertebrae from neck to
sacrum
 Anterior ligament
• Broad, strongly attached to bony vertebrae and discs
• Besides support, prevents hyperextension (bending too far backward) of spine
 Posterior ligament
• Narrow and relatively weak
• Resists hyperflexion (bending too sharply forward) of spine
• Ligamentum flavum
•
Connects adjacent vertebrae
•
Contains elastic connective tissue, especially strong
•
Stretches upon bending forward, recoils on resumption of erect posture
• Short ligaments
•
Connect each vertebra to those above and below
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Major Ligaments Of The Vertebral Column
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Intervertebral Discs
 Cushion-like pad composed of two parts
1.
Nucleus pulposus
•
2.
Inner gelatinous nucleus that gives the disc its elasticity and
compressibility
Anulus fibrosus
•
Strong outer collar surrounding nucleus pulposus
•
Composed of collagen fibers superficially and fibrocartilage
internally
•
Limits the expansion of the nucleus pulposus when spine is
compressed
•
Binds successive vertebrae together, withstands twisting forces,
resists tension in spine

Act as shock absorbers during running, walking and jumping

Allow spine to flex, extend, and bend laterally (to some extent). Thickest in
cervical and lumbar regions

Flatten and bulge out between vertebrae at points of compression
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Median Section Of Three Vertebrae, Illustrating The Composition Of Discs and Ligaments
Supraspinous ligament
Transverse process
Sectioned
spinous process
Ligamentum flavum
Interspinous
ligament
Inferior articular process
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Intervertebral
disc
Anterior
longitudinal
ligament
Intervertebral foramen
Posterior longitudinal
ligament
Anulus fibrosus
Nucleus pulposus
Sectioned body
of vertebra
Figure 7.17a
Herniated (Prolapsed) Disc
• Common name: slipped disc
• Anulus fibrosus ruptures
• Nucleus pulposus protrudes
through anulus
Vertebral spinous process
(posterior aspect of vertebra)
Spinal cord
• If protrusion presses on spinal
cord or spinal nerves exiting the
cord, numbness or excruciating
pain result
Spinal nerve root
• Generally treated with moderate
exercise, massage, heat
therapy, painkillers
Herniated portion
of disc
• Protruding disc may sometimes
have to be removed surgically
and a bone graft done to fuse
the adjoining vertebrae
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Transverse
process
Anulus fibrosus
of disc
Nucleus
pulposus
of disc
(c) Superior view of a herniated intervertebral disc
General Structure of Vertebrae
• Body or centrum
Seven processes per vertebra:
 Anterior weight-bearing region
• Vertebral arch
 Composed of pedicles (short
bony pillars) and laminae (flat
plates) that, along with
centrum, enclose vertebral
foramen
• Vertebral foramina
 Together make up vertebral
canal for spinal cord
•
Spinous process—median posterior projection
•
Transverse processes (2)—project laterally
•
Superior articular processes (2)—protrude superiorly
•
Inferior articular processes (2)—protrude inferiorly
Facets covered with hyaline cartilage
Posterior
Lamina
Spinous
process
Transverse
process
Vertebral
arch
• Intervertebral foramina
 Lateral openings between
adjacent vertebrae (formed by
notches on the superior and
inferior border of pedicles) for
spinal nerves issuing from
spinal cord
Superior
articular
process
and
facet
Vertebral
foramen
Pedicle
Body
(centrum)
Anterior
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Cervical Vertebrae
• C1 to C7: smallest, lightest vertebrae
• C3 to C7 share the following features
 Oval body, wider from side to side
 Spinous processes short and bifid
(except C7)
 Large, triangular vertebral foramen
 Transverse foramen in each
transverse process for passage of
vertebral arteries that supply blood
to the brain
NOTE: Spinous process of C7 is much larger than the
other cervical vertebrae, and is plalpable through the skin,
C7can be used as a landmark for counting the vertebrae
and is called the vertebra prominens.
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Cervical Vertebrae
• C1 (atlas) and C2 (axis) have unique features
• Atlas (C1)
 Ring of bone, no body or spinous process
 Consists of anterior and posterior arches, and two lateral masses
 Superior surfaces of lateral masses articulate with the occipital condyles of
skull, to allow the head to nod “yes”.
 Inferior articular facets form joints with the axis (C2 ) below.
C1
Posterior
Lateral
masses
Posterior
Posterior
tubercle
Posterior arch
Anterior
tubercle
(a) Superior view of atlas (C1)
Anterior arch
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Transverse
foramen
Superior
articular
facet
Posterior arch
Transverse
process
Lateral
masses
Posterior
tubercle
Inferior
articular
facet
Transverse
Anterior
foramen
arch
Facet for dens
Anterior tubercle
(b) Inferior view of atlas (C1)
Dens of axis
Transverse ligament
of atlas
C1 (atlas)
C2 (axis)
C3
Inferior articular
process
Bifid spinous
process
Transverse processes
C7 (vertebra
prominens)
(a) Cervical vertebrae
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Figure 7.20a
Cervical Vertebrae
• Axis (C2)
 Knob-like dens projects superiorly into the anterior arch of atlas
 Dens is the “missing” body of the atlas which fuses with the axis during
embryogenesis
 Dens is cradled in anterior arch of atlas by transverse ligaments and acts as a
pivot for rotation of atlas. [Head can move from side to side, to indicate “no”.]
Posterior
C2
Spinous process
Inferior
articular
process
Lamina
Pedicle
Transverse
process
Dens
Body
(c) Superior view of axis (C2)
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Superior
articular
facet
Thoracic Vertebrae
• T1 to T12
• First T1 looks like C7; last 4 look more like
lumbar vertebrae
• Heart-shaped body with two demifacets
(superior and inferior costal facet).
• Demifacets receive head of ribs [T10 – T 12
have a single facet to receive their
respective ribs]
• Circular vertebral foramen
• Long spinous process, pointing
downwards
• Transverse processes with facets (except
T11 – T 12 ]
• Location of articular facets in frontal plane
prevents flexion and extension, but allows
rotation of this area of spine
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Transverse
process
Superior articular
process
Transverse
costal facet (for
tubercle of rib)
Intervertebral
disc
Body
Spinous
process
Inferior costal
facet (for head
of rib)
Inferior articular
process
(b) Thoracic vertebrae
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Figure 7.20b
Lumbar Vertebrae
• L1 to L5
• Weight bearing, receive most
stress
• Massive kidney-shaped bodies
• Short, thick pedicles and laminae
• Robust flat hatchet-shaped
spinous processes project
backwards for attachment of large
back muscles
• Orientation of articular facets locks
lumbar vertebrae together so as to
prevent rotation while allowing
flexion and extension
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Superior
articular
process
Transverse
process
Body
Intervertebral
disc
Inferior
articular
process
Spinous
process
(c) Lumbar vertebrae
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Figure 7.20c
Sacrum and Coccyx
Sacral promontory
Sacrum
Ala
•
Triangular structure representing 5 fused
vertebrae (S1–S5), forms posterior wall of pelvis
•
Articulates with L5 superiorly (via its superior
articular process) and with coccyx inferiorly
•
Articulates laterally with auricular surfaces of hip
bones to form sacroiliac joints of pelvis
•
Four transverse ridges in anterior aspect mark
lines of fusion of sacral vertebrae
•
Anterior sacral foramina at lateral ends of
ridges transmit blood vessels and anterior rami of
sacral spinal nerves
•
Posterior midline roughened by medial sacral
crest (fused spinous processes of sacral
vertebrae)
•
Sacral crest flanked laterally by posterior sacral
foramina (which transmit posterior rami of sacral
spinal nerves) and lateral sacral crests
(remnants of transverse processes of S1–S5
•
Vertebral canal continues inside as sacral canal
•
Sacral hiatus, an enlarged external opening at
inferior end of sacral canal represents area where
laminae of 5th sacral vertebrae fail to fuse
medially
Body of
first
sacral
vertebra
Transverse
ridges (sites
of vertebral
fusion)
Apex
Coccyx
(a) Anterior view
Ala
Sacral
canal
Median
sacral
crest
Posterior
sacral
foramina
Coccyx
(b) Posterior view
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Anterior
sacral
foramina
Body
Facet of
superior
articular
process
Auricular
surface
Lateral
sacral
crest
Sacral
hiatus
Coccyx
• Tailbone
• Small, triangular, formed by 3-5
fused vertebrae
• Articulates superiorly with
sacrum
• Provides slight support to pelvic
organs, but otherwise useless
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Thoracic Cage
Roughly cone-shaped, with broad dimensions positioned posteriorly
Composed of
•
Thoracic vertebrae dorsally
•
Sternum costal cartilages anteriorly
•
Ribs laterally
NOTE: Costal cartilages secure ribs to sternum
Functions
• Protective cage around vital organs (heart, lung, great blood vessels) of
thoracic cavity
• Supports shoulder girdle and upper limbs
• Provides attachment sites for many muscles of neck, back, chest and
shoulders
• Intercostal muscles in intercostal spaces between ribs used to lift and
depress thorax during breathing
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Sternum (Breastbone)
• Lies in anterior midline of thorax
• Flat bone resembling a dagger
• Formed by fusion of three
bones
 Manubrium: Articulates with
clavicles and ribs 1 and 2
 Body: Articulates with costal
cartilages of ribs 2 through 7
 Xiphoid process: Site of
muscle attachment, not
ossified until ~ age 40
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Ribs and Their Attachments
• 12 pairs
• All attach posteriorly to thoracic vertebrae
• Pairs 1 through 7: True (vertebrosternal) ribs, attach directly to
sternum by individual costal cartilages
• Pairs 8 through12: False ribs
• Pairs 8–10: Also called vertebrochondral ribs, attach indirectly to
sternum by joining costal cartilage of rib above
• Pairs 11–12 also called vertebral (floating) ribs, have no
attachment to sternum
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Ribs and Their Attachments
Jugular notch
Clavicular notch
Manubrium
Sternal angle
Body
Xiphisternal Sternum
joint
Xiphoid
process
True
ribs
(1–7)
False
ribs
(8–12)
Intercostal spaces
Costal cartilage
Costal margin
L1
Vertebra
Floating ribs (11, 12)
(a) Skeleton of the thoracic cage, anterior view
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Figure 7.22a
Structure of a Typical Rib
Main parts:
•
Head: Articulates posteriorly with facets
(demifacets) on bodies of two adjacent vertebrae
•
Neck
•
Tubercle: Articulates posteriorly with transverse
costal facet of same-numbered thoracic vertebra
•
Transverse costal facet
(for tubercle of rib)
Angle
of rib
Superior costal facet
(for head of rib)
Body of vertebra
Head of rib
Intervertebral disc
Neck of rib
Tubercle of rib
Shaft
Shaft Sternum
Crosssection
of rib
Costal groove Costal cartilage
(a) Vertebral and sternal articulations of a
typical true rib
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Structure of a Typical Rib
Main parts:
•
Head: Articulates posteriorly with facets (demifacets) on bodies of two adjacent vertebrae
•
Neck
•
Tubercle: Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra
•
Shaft
Transverse costal facet
(for tubercle of rib)
Angle
of rib
Superior costal facet
(for head of rib)
Articular facet
on tubercle of rib
Spinous process
Shaft
Body of vertebra
Head of rib
Intervertebral disc
Neck of rib
Tubercle of rib
Shaft Sternum
Ligaments
Neck of rib
Head of rib
Crosssection
of rib
Costal groove Costal cartilage
(a) Vertebral and sternal articulations of a
typical true rib
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Transverse
costal facet
(for tubercle
of rib)
Body of
thoracic
vertebra
Superior costal facet
(for head of rib)
(b) Superior view of the articulation between a
rib and a thoracic vertebra
Figure 7.23b