The Axial and Appendicular Skeleton: A Comprehensive Overview

1. The Axial Skeleton (contd.) & The Appendicular Skeleton Human Anatomy Sonya Schuh-Huerta, Ph.D.

2. The Vertebral Column • Formed from 26 bones in the adult • Transmits weight of trunk to lower limbs • Surrounds & protects spinal cord

3. The Vertebral Column • Serves as attachment sites for muscles of the neck and back • Held in place by ligaments • Anterior & posterior longitudinal ligaments • Ligamentum flavum

4. The Vertebral Column C1 2 Cervical curvature (concave) 7 vertebrae, C1 – C7 3 4 5 6 7 Spinous process T 1 2 Transverse processes 3 4 Thoracic curvature (convex) 12 vertebrae, T1 – T12 5 6 7 8 9 Intervertebral discs 10 11 Intervertebral foramen 12 L 1 Lumbar curvature (concave) 5 vertebrae, L1 – L5 2 3 4 5 Sacral curvature (convex) 5 fused vertebrae sacrum Coccyx 4 fused vertebrae Anterior view Right lateral view

5. Regions & Normal Curvatures • The Vertebral column has 5 major regions • 7 cervical vertebrae of the neck region • 12 thoracic vertebrae • 5 lumbar vertebrae • Sacrum  five fused bones • Inferior to lumbar vertebrae • Coccyx  inferior to sacrum

6. Regions & Normal Curvatures • Curvatures of the spine • Cervical & lumbar curvatures • Concave posteriorly • Thoracic & sacral curvatures • Convex posteriorly

7. Regions & Normal Curvatures • Curvatures increase resilience of spine • Thoracic & sacral curvatures • Primary curvatures • Present at birth • Lumbar curvature • Develops when baby begins to walk (~1 year)

8. Ligaments of the Spine • Major supporting ligaments • Anterior longitudinal ligament • Attaches to bony vertebrae & intervertebral discs • Prevents hyperextension • Posterior longitudinal ligament • Narrow & relatively weak • Attaches to intervertebral discs

9. Ligaments of the Spine Intervertebral disc Supraspinous ligament Anterior longitudinal ligament Transverse process Sectioned spinous process Intervertebral foramen Posterior longitudinal ligament Ligamentum flavum Interspinous ligament Anulus fibrosus Nucleus pulposus Inferior articular process Sectioned body of vertebra Posterior longitudinal ligament (a) Median section of three vertebrae, illustrating the composition of the discs and the ligaments Anterior longitudinal ligament Body of a vertebra Intervertebral disc (b) Anterior view of part of the spinal column

10. Intervertebral Discs • Are cushion-like pads between vertebrae • Composed of: • Nucleus pulposus • Anulus fibrosus

11. Intervertebral Discs • Nucleus pulposus  • derived from notocord • Gelatinous inner sphere • Absorbs compressive stresses • Annulus fibrosus • Outer rings formed of ligament • Inner rings formed of fibrocartilage • Surround the nucleus pulposus

12. Intervertebral Disc Vertebral spinous process (posterior aspect of vertebra) Spinal cord Spinal nerve root Nucleus pulposus of intact disc Transverse process Herniated portion of disc Anulus fibrosus of disc Nucleus pulposus of disc Herniated nucleus pulposus (c) Superior view of a herniated intervertebral disc • MRI of lumbar region of vertebral column in • sagittal section showing normal & • herniated discs

13. General Structure of Vertebrae Posterior Lamina Vertebral arch Spinous process Transverse process Superior articular process and facet Pedicle Vertebral foramen Body (centrum) Anterior

14. General Structure of Vertebrae • Common structures to all regions • Body • Vertebral arch • Vertebral foramen • Spinous process • Transverse process • Superior & inferior articular processes • Intervertebral foramina

15. Movement of the Vertebrae • Specific regions of the spine perform specific functions • Types of movement that occur between vertebrae • Flexion & extension • Lateral flexion • Rotation in the long axis

16. Cervical Vertebrae • 7 cervical vertebrae (C1–C7)  smallest & lightest vertebrae • C3–C7 are typical cervical vertebrae • Body is wider laterally • Spinous processes are short & bifid (except C7) • Vertebral foramen are large & triangular • Transverse processes contain transverse foramina • Superior articular facets face superoposteriorly

17. Cervical Vertebrae

18. 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

19. The Atlas • C1 is termed atlas • Lacks a body & spinous process • Supports the skull • Superior articular facets receive the occipital condyles • Allows flexion & extension of neck • Nodding the head “yes”

20. The Atlas Posterior C1 Posterior tubercle Posterior arch Lateral masses Transverse foramen Superior articular facet Anterior arch Anterior tubercle (a) Superior view of atlas (C1)

21. The Atlas C1 Posterior Posterior tubercle Posterior arch Inferior articular facet Transverse process Lateral masses Anterior Transverse foramen arch Facet for dens Anterior tubercle (b) Inferior view of atlas (C1)

22. The Axis • Has a body & spinous process • Dens (odontoid process) projects superiorly • Formed from fusion of the body of the atlas with the axis • Acts as a pivot for rotation of the atlas & skull • Participates in rotating the head from side to side (‘nodding no’)

23. The Axis Posterior C2 Spinous process Lamina Inferior articular process Pedicle Superior articular facet Transverse process Body Dens (c) Superior view of axis (C2)

24. Thoracic Vertebrae (T1—T12) • All articulate with ribs • Have heart-shaped bodies from the superior view • Each side of the body of T1–T10 bears demifacts for articulation with ribs • T1 has a full facet for the first rib • T10–T12 only have a single facet

25. Thoracic Vertebrae

26. Thoracic Vertebrae • Spinous processes are long & point inferiorly • Vertebral foramen are circular • Transverse processes articulate with tubercles of ribs • Superior articular facets point posteriorly • Inferior articular processes point anteriorly • Allows rotation & prevents flexion and extension

27. Lumbar Vertebrae (L1—L5) • Bodies are thick & robust • Transverse processes are thin & tapered • Spinous processes are thick, blunt, & point posteriorly • Vertebral foramina are triangular • Superior & inferior articular facets directly medially • Allows flexion & extension  rotation prevented

28. Lumbar Vertebrae

29. Lumbar Vertebrae Superior articular process Body Transverse process Intervertebral disc Inferior articular process Spinous process (c) Lumbar vertebrae

30. Sacrum (S1—S5) • Shapes the posterior wall of pelvis • Formed from 5 fused vertebrae • Superior surface articulates with L5 • Inferiorly articulates with coccyx • Sacral promontory • Where the first sacral vertebrae bulges into pelvic cavity • Center of gravity is 1 cm posterior to sacral promontory • Ala develops from fused rib elements

31. Sacrum • Sacral foramina • Ventral foramina • Passage for ventral rami of sacral spinal nerves • Dorsal foramina • Passage for dorsal rami of sacral spinal nerves

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

33. Coccyx • Is the “tailbone” • Formed from 3–5 fused vertebrae • Offers only slight support to pelvic organs • Easily injured

34. The Thoracic Cage • Forms the framework of the chest • Components • Thoracic vertebrae – posteriorly • Ribs – laterally • Sternum and costal cartilage – anteriorly • Protects thoracic organs • Supports shoulder girdle and upper limbs • Provides attachment sites for muscles

35. The Thoracic Cage Jugular notch Clavicular notch Manubrium Sternal angle Body Sternum Xiphisternal joint True ribs (1–7 Xiphoid process False ribs (8–12) Intercostal spaces L1 Vertebra Costal cartilage Costal margin Floating ribs (11, 12) (a) Skeleton of the thoracic cage, anterior view

36. The Thoracic Cage T2 Jugular notch T3 Sternal angle T4 Heart Xiphisternal Xiphisternal joint T9 (b) Midsagittal section through the thorax, showing the relationship of surface anatomical landmarks of the thorax to the vertebral column

37. Sternum • Formed from three sections • Manubrium—superior section • Articulates with medial end of clavicles • Body—bulk of sternum • Sides are notched at articulations for costal cartilage of ribs 2–7 • Xiphoid process—inferior end of sternum • Ossifies around age 40

38. Sternum • Anatomical landmarks • Jugular notch • Central indentation at superior border of the manubrium • Sternal angle • A horizontal ridge where the manubrium joins the body • Xiphisternal joint • Where sternal body and xiphoid process fuse • Lies at the level of the 9th thoracic vertebra

39. Ribs • All ribs attach to vertebral column posteriorly • True ribs - superior seven pairs of ribs • Attach to sternum by costal cartilage • False ribs—inferior five pairs of ribs • Ribs 11–12 are known as floating ribs

40. Ribs Facets for articulation with vertebrae Articular facet on tubercle Head Neck Shaft Costal angle Junction with costal cartilage Costal groove (a) A typical rib (rib 6, right), posterior view Transverse costal facet (for tubercle of rib) Superior costal facet (for head of rib) Angle of rib Body of vertebra Head of rib Intervertebral disc Neck of rib Tubercle of rib Shaft Sternum Cross- section of rib Costal groove Costal cartilage (b) Vertebral and sternal articulations of a typical true rib

41. Ribs Articular facet on tubercle of rib Spinous process Shaft Transverse costal facet (for tubercle of rib) Ligaments Neck of rib Body of thoracic vertebra Head of rib Superior costal facet (for head of rib) (c) Superior view of the articulation between a rib and a thoracic vertebra

42. Disorders of the Axial Skeleton • Cleft palate • A common congenital disorder • Right & left halves of palate fail to fuse medially • Can involve entire palate & lip – minor to severe • Stenosis of the lumbar spine • Narrowing of the vertebral canal • Can compress roots of spinal nerves

43. Disorders of the Axial Skeleton • Abnormal spinal curvatures • Scoliosis—an abnormal lateral curvature • Kyphosis—an exaggerated thoracic curvature • Lordosis—an accentuated lumbar curvature; “swayback”

44. The Axial Skeleton Throughout Life • Membrane bones begin to ossify in second month of development • Bone tissue grows outward from ossification centers • Fontanels • Unossified remnants of membranes

45. Fontanelles Frontal suture Frontal bone Anterior fontanelle Ossification center Parietal bone Posterior fontanelle Occipital bone (a) Superior view

46. Fontanelles Parietal bone Frontal bone Ossification center Sphenoidal fontanelle Posterior fontanelle Temporal bone (squamous portion) Mastoid fontanelle Occipital bone (b) Lateral view

47. The Axial Skeleton Throughout Life • Many bones of the face & skull form by intramembranous ossification • Endochondral bones of the skull are: • Occipital bone • Sphenoid • Ethmoid bones • Parts of the temporal bone

48. The Axial Skeleton Throughout Life • Aging of the axial skeleton: • Water content of the intervertebral discs decreases • By age 55, loss of a few centimeters in height is common! • Thorax becomes more rigid • Bones lose mass with age

49. The Appendicular Skeleton, Ch 8 (also to be used as Lab Guide)

50. The Appendicular Skeleton • Pectoral girdle • Attaches the upper limbs to the trunk • Pelvic girdle • Attaches the lower limbs to the trunk • Upper & lower limbs differ in function • Share the same structural plan