1. Chapter 7 The Skeleton Part B Shilla Chakrabarty, Ph.D.

2. 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

3. Vertebral Column: Curvatures
Cervical curvature
(concave)
7 vertebrae, C1–C7
Thoracic
curvature
(convex)
12 vertebrae,
T1–T12
Lumbar curvature
5 vertebrae, L1–L5
Sacral curvature
5 fused vertebrae
sacrum
Coccyx
4 fused vertebrae
Anterior view
Right lateral view
Spinous
process
Transverse
processes
Intervertebral
discs
foramen C1
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

4. 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

5. Major Ligaments Of The Vertebral Column

6. Intervertebral Discs Cushion-like pad composed of two parts
Nucleus pulposus
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

7. Supraspinous ligament Intervertebral disc
Median Section Of Three Vertebrae, Illustrating The Composition Of Discs and Ligaments
Supraspinous ligament
Intervertebral
disc
Anterior
longitudinal
ligament
Intervertebral foramen
Posterior longitudinal
Anulus fibrosus
Nucleus pulposus
Sectioned body
of vertebra
Transverse process
Sectioned
spinous process
Ligamentum flavum
Interspinous
Inferior articular process
Figure 7.17a

8. Herniated (Prolapsed) Disc
Common name: slipped disc
Anulus fibrosus ruptures
Nucleus pulposus protrudes through anulus
If protrusion presses on spinal cord or spinal nerves exiting the cord, numbness or excruciating pain result
Generally treated with moderate exercise, massage, heat therapy, painkillers
Protruding disc may sometimes have to be removed surgically and a bone graft done to fuse the adjoining vertebrae
Vertebral spinous process
(posterior aspect of vertebra)
Spinal nerve root
Anulus fibrosus
of disc
Herniated portion
Nucleus
pulposus
Spinal cord
(c) Superior view of a herniated intervertebral disc
Transverse
process

9. General Structure of Vertebrae
Body or centrum
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
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
Seven processes per vertebra:
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
Anterior
Lamina
Superior
articular
process
and
facet
Transverse
Pedicle
Spinous
Vertebral
arch
foramen
Body
(centrum)

10. 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.

11. 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.
Anterior arch
Superior
articular
facet
Transverse
foramen
Posterior arch
Posterior
tubercle
Anterior
Lateral
masses
(a) Superior view of atlas (C1) C1
Facet for dens
process
Anterior tubercle
arch
(b) Inferior view of atlas (C1)
Inferior

12. (a) Cervical vertebrae
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
Figure 7.20a

13. 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”.] C2
Posterior
Dens
(c) Superior view of axis (C2)
Inferior
articular
process
Body
Superior
facet
Transverse
Pedicle
Lamina
Spinous process

14. 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

15. (b) Thoracic vertebrae
Superior articular
process
Transverse
process
Transverse
costal facet (for
tubercle of rib)
Intervertebral
disc
Body
Inferior costal
facet (for head
of rib)
Spinous
process
Inferior articular
process
(b) Thoracic vertebrae
Figure 7.20b

16. 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

17. Superior articular process Transverse Body process Intervertebral disc
Inferior
articular
process
Spinous
process
(c) Lumbar vertebrae
Figure 7.20c

18. Sacrum and Coccyx Coccyx Anterior sacral foramina Apex
Sacral promontory
Ala
Body of
first
vertebra
Transverse
ridges (sites
of vertebral
fusion)
(a) Anterior view
Sacrum
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
Coccyx
Posterior
sacral
foramina
Median
crest
Sacral
canal
hiatus
Body
Facet of
superior
articular
process
Lateral
Auricular
surface
Ala
(b) Posterior view

19. Coccyx Tailbone Small, triangular, formed by 3-5 fused vertebrae
Articulates superiorly with sacrum
Provides slight support to pelvic organs, but otherwise useless

20. 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

21. 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

22. 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

23. Ribs and Their Attachments
Intercostal spaces
True
ribs
(1–7)
False
(8–12)
Jugular notch
Clavicular notch
Manubrium
Sternal angle
Body
Xiphisternal
joint
Xiphoid
process L1
Vertebra
Floating ribs (11, 12)
Sternum
Costal cartilage
Costal margin
(a) Skeleton of the thoracic cage, anterior view
Figure 7.22a

24. 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)
Superior costal facet
(for head of rib)
Body of vertebra
Head of rib
Intervertebral disc
Tubercle of rib
Neck of rib
Shaft
Sternum
Angle
of rib
Cross-
section
Costal groove
Costal cartilage
(a) Vertebral and sternal articulations of a typical true rib

25. 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)
Superior costal facet
(for head of rib)
Body of vertebra
Head of rib
Intervertebral disc
Tubercle of rib
Neck of rib
Shaft
Sternum
Angle
of rib
Cross-
section
Costal groove
Costal cartilage
(a) Vertebral and sternal articulations of a typical true rib
Figure 7.23b
Spinous process
Articular facet
on tubercle of rib
Shaft
Ligaments
Neck of rib
Head of rib
Body of
thoracic
vertebra
Transverse
costal facet
(for tubercle
of rib)
Superior costal facet
(for head of rib)
(b) Superior view of the articulation between a rib and a thoracic vertebra