SM

Skeletal System - Quick Reference

The Skeletal System

  • Overview: framework of the body; consists of bones and supporting tissues.

The Skeleton

  • Two divisions: Axial and Appendicular
  • System includes: Joints, Cartilage, Ligaments
  • Subsystems: Appendicular Skeleton, Axial Skeleton

Functions of Bones

  • Support: framework (legs support trunk; rib cage supports thoracic wall)
  • Protection: skull, vertebrae, rib cage
  • Movement: skeletal muscles/tendons; bones as levers
  • Joints enable movement; without joints bones would be rigid
  • Storage: fat, calcium and phosphorus
  • Marrow: site of hematopoiesis (blood cell formation)

Bone Classification

  • Adults have 206 bones
  • Two types of osseous tissue: Compact Bone, Spongy Bone
  • 4 Shapes: 4 Shapes: Long, Short, Flat, Irregular

Long Bones

  • Typically longer than wide
  • Include: shaft (diaphysis) and two ends (epiphyses/heads)
  • Mostly compact bone
  • All bones of limbs except patella, carpal (wrist), and tarsal (ankle) bones

Short Bones

  • Generally cube-shaped
  • Mostly spongy bone
  • Includes wrist and ankle bones
  • Sesamoid bones form within tendons (e.g., patella)

Flat Bones

  • Thin, flattened, curved
  • Two thin layers of compact bone with a middle layer of spongy bone
  • Includes most skull bones, ribs, sternum

Irregular Bones

  • Do not fit into the other categories
  • Examples: Ethmoid, Sphenoid, Palatine, Temporal, Inferior nasal concha, Zygomatic, Hyoid, Maxilla, Mandible, Vertebrae, Sacrum

Structure of a Long Bone

  • Diaphysis (shaft): main length; compact bone
  • Periosteum: outer covering; Sharpey's fibers secure periosteum to bone
  • Epiphyses (ends): thin layer of compact bone enclosing spongy bone
  • Articular cartilage (hyaline): reduces friction at joints

Growth and Internal Structure

  • Epiphyseal line in adults: remnant of the epiphyseal plate; growth in length occurs at the plate during development; cartilage is replaced by bone after growth
  • Endosteum: inner lining of the shaft
  • Medullary (marrow) cavity: contains yellow marrow (fat)
  • Red marrow: in adults, in spongy bone of flat bones and epiphyses of some long bones; in infants, produces red blood cells

Additional Bone Features (Cross-Section)

  • Proximal and distal epiphyses; articular cartilage; epiphyseal line; spongy bone; compact bone; periosteum; medullary cavity; endosteum; nutrient arteries

Bone Markings

  • Markings reveal where muscles, tendons, and ligaments attach and where blood vessels and nerves pass
  • Two types: projections/ Processes; depressions/ Cavities