copyright © 2010 pearson education, inc. chapter 7 the skeleton part b shilla chakrabarty, ph.d

Copyright © 2010 Pearson Education, Inc.

Chapter 7

The Skeleton

Part B

Shilla Chakrabarty, Ph.D.


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


Cervical curvature (concave)7 vertebrae, C1–C7

Thoracic curvature(convex)12 vertebrae,T1–T12

Lumbar curvature(concave)5 vertebrae, L1–L5

Sacral curvature(convex)5 fused vertebrae sacrum

Coccyx4 fused vertebrae

Anterior view Right lateral view

Spinousprocess

Transverseprocesses

Intervertebraldiscs

Intervertebralforamen

C1

Vertebral Column: Curvatures

Increase the resilience and flexibility of the spine

Two posteriorly concave curvatures:

Cervical and lumbar

Two posteriorly convex curvatures:

Thoracic and sacral

Abnormal spine curvaturesScoliosis (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


• 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

Ligaments


Major Ligaments Of The Vertebral Column


Intervertebral DiscsCushion-like pad composed of two parts

1. Nucleus pulposus

• Inner gelatinous nucleus that gives the disc its elasticity and compressibility

2. 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

Copyright © 2010 Pearson Education, Inc. Figure 7.17a

Supraspinous ligamentIntervertebraldisc

Anteriorlongitudinalligament

Intervertebral foramen

Posterior longitudinalligament

Anulus fibrosus

Nucleus pulposus

Sectioned bodyof vertebra

Transverse process

Sectionedspinous process

Ligamentum flavum

Interspinousligament

Inferior articular process

Median Section Of Three Vertebrae, Illustrating The Composition Of Discs and Ligaments


Vertebral spinous process(posterior aspect of vertebra)

Spinal nerve root

Anulus fibrosusof disc

Herniated portionof disc

Nucleuspulposusof disc

Spinal cord

(c) Superior view of a herniated intervertebral disc

Transverseprocess

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


General Structure of Vertebrae

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

Superiorarticularprocessandfacet

Transverseprocess

Pedicle

Spinousprocess

Vertebralarch

Vertebralforamen

Body(centrum)

• 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


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.


Anterior arch

Superiorarticularfacet

Transverseforamen

Posterior arch

Posteriortubercle

Anteriortubercle

Posterior

Lateralmasses

(a) Superior view of atlas (C1)

C1

Facet for dens

Transverseprocess

Lateralmasses

Transverseforamen

Posterior archPosteriortubercle

Posterior

Anterior tubercle

Anteriorarch

(b) Inferior view of atlas (C1)

Inferiorarticularfacet

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.


Dens of axis

Transverse ligamentof atlasC1 (atlas)

C2 (axis)

Bifid spinousprocess

Transverse processes

C7 (vertebraprominens)

(a) Cervical vertebrae

C3

Inferior articularprocess


C2

Posterior

Dens

(c) Superior view of axis (C2)

Inferiorarticularprocess

Body

Superiorarticularfacet

Transverseprocess

Pedicle

Lamina

Spinous process

• 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”.]

Cervical Vertebrae


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

Copyright © 2010 Pearson Education, Inc. Figure 7.20b

Transverseprocess

Spinousprocess

Superior articularprocess

Transversecostal facet (fortubercle of rib)

Body

Intervertebraldisc

Inferior costalfacet (for headof rib)Inferior articularprocess

(b) Thoracic vertebrae


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

Copyright © 2010 Pearson Education, Inc. Figure 7.20c

Superiorarticularprocess

Transverseprocess

Spinousprocess

Intervertebraldisc

Body

Inferiorarticularprocess

(c) Lumbar vertebrae


Sacrum and CoccyxSacrum

• 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

Anteriorsacralforamina

Apex

Sacral promontory

AlaBody offirstsacralvertebra

Transverseridges (sites of vertebral fusion)

(a) Anterior view

Coccyx

Posteriorsacralforamina

Mediansacralcrest

Sacralcanal

Sacralhiatus

Body Facet ofsuperiorarticular process

Lateralsacralcrest

Auricularsurface

Ala

(b) Posterior view


Coccyx

• Tailbone

• Small, triangular, formed by 3-5 fused vertebrae

• Articulates superiorly with sacrum

• Provides slight support to pelvic organs, but otherwise useless


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


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


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


(a) Skeleton of the thoracic cage, anterior view

Intercostal spaces

Trueribs(1–7)

Falseribs(8–12)

Jugular notchClavicular notch

ManubriumSternal angleBodyXiphisternaljointXiphoidprocess

L1

Vertebra Floating ribs (11, 12)

Sternum

Costal cartilageCostal margin

Ribs and Their Attachments


Structure of a Typical RibMain 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

ShaftSternum

Angleof rib

Cross-sectionof rib

Costal groove Costal cartilage

(a) Vertebral and sternal articulations of atypical true rib

Copyright © 2010 Pearson Education, Inc. Figure 7.23b

Spinous processArticular faceton tubercle of rib

Shaft

Ligaments

Neck of rib

Head of ribBody ofthoracicvertebra

Transversecostal facet(for tubercleof rib)

Superior costal facet(for head of rib)

(b) Superior view of the articulation between arib and a thoracic vertebra

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

ShaftSternum

Angleof rib

Cross-sectionof rib

Costal groove Costal cartilage

(a) Vertebral and sternal articulations of atypical true 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

Structure of a Typical Rib

copyright © 2010 pearson education, inc. chapter 7 the skeleton part b shilla chakrabarty, ph.d

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