Chapter 5 Skeletal System: Bones, Functions and Microscopic Anatomy

Skeletal System includes joints, bones, cartilage, ligaments The skeleton has two sub-divisions of 206 bones : Axial —forms the longitudinal axis of the skeleton Appendicular —forms the limbs and girdles

Axial Subdivision Think of a straight line down From the top of the head through the pelvis: --Head --Vertebrae --Ribcage

Appendicular Subdivision Think arms and legs

Functions of the Skeletal System Functions of the bones:  Support  Protection —protect soft organs  Movements —bones are used as levers by muscles to move the body  Storage —fat is stored in the internal cavities of bones  Minerals are also stored : Calcium & Phosphorus  Blood Cell Formation —Hematopoiesis occurs within marrow cavities

Shapes of Bones There are 4 distinct shapes of bones in the body: --Long --Short --Flat --Irregular

Long Bones  typically longer than they are wide  Mostly made up of compact bone  Ex.) bones of the arm and leg

Short Bones  cube shaped & mostly spongy bone  Ex.) bones of the wrist and ankle

Flat Bones  thin, flat and usually curved * 2 layers of compact bone, over 1 layer of spongy bone (Pelvis, Scapula, Cranium)

Irregular Bones  Those bones that don’t fit into the other categories **Ex.) Vertbrae and Hip bones

Bone Tissue In the body, there are two forms of bone tissue: Compact Bone—Dense Tissue that smooth look Spongy Bone—Composed of small needlelike pieces of bone and space

Compact Bone

Spongy Bone

Bone Markings Bone Markings  Bumps, holes and ridges on bone that serve a specific purpose 2 Categories  1.) Projections / Processes —grow out from the surface 2.) Depressions / Cavities —indentations into the bone

Structure of a Long Shaft Bone Diaphysis —Shaft of a long bone Epiphysis —the end of a long shaft bone Periosteum —connective tissue membrane covering the diaphysis shaft Sharpey’s Fibers —connect the periosteum to the diaphysis (acts as a glue to anchor the periosteum)

Structure of a Long Shaft Bone  Articular Cartilage —covers the epiphysis surface   provides a smooth slippery surface that decreases friction at joint surfaces  Epiphyseal Line —found in adult bones, in the epiphysis  Epiphyseal Plate —found in developing, young bones

Structure of a Long Shaft Bone  Medullary Cavity —the central cavity of the long shaft of long bones  Yellow marrow —storage area of fat in the cavity of the shaft in adults  Red Marrow —forms red blood cells (in medullary cavity in young bones)

Microscopic Anatomy of the Bone  Osteocytes —mature bone cells are found in lacuna  Lacuna —tiny cavities found within the matrix  Lamellae —concentric circles of matrix surrounding an artery and canal  Haversian System (Osteon)—central canal + matrix rings  Canaliculi —Radiating canals that connect all bone cells to the nutrient supply  Volkmann’s Canals —run into the compact bone at right angles to the shaft