Biology 110 Chapter 6 The Skeletal System



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Biology 110 Chapter 6

The Skeletal System


  1. Skeleton: Overview




  1. Functions




  1. Support




  1. Protection

  1. Cranium – brain

  2. Vertebrae – spinal cord

  3. Ribs – organs of thoracic cavity and upper abdominal cavity

  4. All – blood cell production centers in the marrow




  1. Blood cell production




  1. Storage

  1. Minerals; calcium primarily but also phosphate




  1. Movement

  1. Sites of attachment for skeletal muscle

  2. Act as levers to facilitate movement




  1. Anatomy of a Long Bone

  1. Periosteum

  2. Epiphysis

  3. Diaphysis

  4. Medullary cavity

  5. Articular cartilage

  6. Compact bone

  1. Arranged in Haversian systems or osteons

  2. Concentric rings of dense bone around a central canal

  1. Central canal contains blood vessels and nerves that enter from periosteum

  2. Connected by Volkmann’s canals to periosteum

  1. Osteoblasts lay down bone, mature into osteocytes

  2. Mineralized matrix traps osteocytes in lacunae

  1. Matrix consists of collagen fibers with calcium salts

  1. Lacunae connected by canaliculi

  1. Spongy bone (cancellous bone)

  1. Trabeculae – bars, plates, spicules of bone

  1. Somewhat less dense than compact bone

  2. Still provide strength by aligning with direction of stress

  1. Red marrow – site of blood cell development

  1. Found in spongy bone of skull, ribs, sternum, vertebrae, and epiphyses of long bones




  1. Growth and Development

  2. Fractures




  1. Classification

  1. Simple: Doesn’t pierce the skin

  2. Compound: Broken ends pierce the skin

  3. Complete: Broken into two parts

  4. Partial: Broken longitudinally but not separated in two

  5. Greenstick: Incomplete break on outer arc of bone

  6. Impacted: Broken ends wedged into each other

  7. Comminuted: Broken into several fragments

  8. Spiral: Ragged break due to twisting of bone




  1. Repair of a Fracture

  1. Hematoma: Clot forms in space between broken bone pieces. Area is inflamed and swollen.

  2. Fibrocartilage callus: Repair; clot replaced by fibrocartilage, bone ends joined by collagen fibers.

  3. Bony callus: Osteoblasts produce trabeculae of spongy bone and convert fibrocartilage to bony callus.

  4. Remodeling: Osteoblasts produce compact bone on outer layer, osteoclasts reabsorb spongy bone to make medullary cavity if needed. Osteoclasts may also reabsorb compact bone to maintain proper shape overall.




  1. Axial Skeleton

  1. Skull

  1. Cranium

  1. Joints = sutures (immovable joints)

  1. Fontanels – membranous regions where 2 or more bones meet

  2. Anterior fontanel – where parietal bones meet frontal bone; usually closes by 2 yrs of age

  3. Permit compression during birth



  1. Frontal bone (1) – forehead, part of nose, superior portions of orbits

  2. Parietal Bones (2) – dorsal to frontal bone, form roof and part of sides of cranium

  3. Occipital Bone (1) Most dorsal part, base of cranium

  1. Foramen magnum – opening through which spinal cord joins brain

  2. Occipital condyles – rounded processes on either side of foramen magnum, articulate with first vertebra (atlas)

  1. Temporal Bones (2) – inferior tyo parietal bones, help form base of cranium

  1. External Auditory meatus – leads to middle ear

  2. Mandibular fossa – artyiculates with mandible

  3. Mastoid process – attachment site for neck muscles

  4. Styloid process – attachment of muscles of tongue and neck

  5. Zygomatic process – helps form cheekbone

  1. Sphenoid Bone (1) sides and base of cranium, floors and sides of orbits

(1) Sella turcica – superior depression, houses pituitary gland

  1. Ethmoid Bone (1) – part of roof of nasal cavity

  1. Crista galli (cock’s comb) – triangular process, attachment site for dura mater

  2. Cribiform plate – passage of olfactory nerves

  3. Perpendicular plate – projects inferiorly, forms nasal septum

  4. Superior and middle nasal conchae – project toward perpendicular plate, (from lateral walls of nasal cavity)



  1. Facial Bones

  1. Maxillae (2) – upper jaw

  1. alveolar processes hold teeth

  2. palatine processes form anterior hard palate

  3. floors of orbits

  4. sides and floor of nasal cavity

  1. Palatine Bones (2) – Posterior portion of hard palate, floor of nasal cavity (cleft palate)

  2. Zygomatic Bones (2) – sides of orbits and cheekbones

  3. Lacrimal Bones (2) – medial walls of orbits

  4. Nasal Bones (2) – form bridge of nose

  5. Vomer Bone (1) – joins perpendicular plate of ethmoid, forms nasal septum

  6. Inferior Nasal Conchae (2) – project into nasal cavities from lateral walls

  7. Mandible

  1. Hyoid Bone

  2. Vertebral Column (Spine)

  3. Thoracic Cage

  1. Appendicular Skeleton

  2. Joints (Articulations)

  3. Medical Focus – Knee Injuries

  4. MedAlert – Arthritic Joints

  5. Effects of Aging

I.Working Together







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