SKELETAL SYSTEM

• Skeletal System


  Components: Bones, Cartilages, Tendons, Ligaments

  
• Bones of the Skeletal System

  • Long bones
  • Short bones
  • Flat bones
  • Irregular bones

  
• Skeletal System Functions


  • Support
  • Protect
  • Movement
  • Storage
  • Blood cell production
• Extracellular Matrix


  Composition: Collagen, ground substance, other organic molecules, water, minerals
• Collagen


  Tough, ropelike protein
• Proteoglycans


  Large molecules consisting of many polysaccharides attaching to and encircling core proteins
• Extracellular Matrix of Tendons and Ligaments

  • Contains large amounts of collagen fibers, making these structures very tough, like ropes or cables
• Extracellular Matrix of Cartilage

  • Contains collagen and proteoglycans. Collagen makes cartilage tough, whereas the water-filled proteoglycans make it smooth and resilient. Cartilage is relatively rigid, but it springs back to its original shape after being bent or slightly compressed. It is an excellent shock absorber.
• Extracellular Matrix of Bone

  • Contains collagen and minerals, including calcium and phosphate. The ropelike collagen fibers lend flexible strength to the bone. The mineral component gives bone compression (weight-bearing) strength. Most of the mineral in bone is in the form of calcium phosphate crystals called hydroxyapatite.

  
• Bone Shape Classifications


  • Long bones
  • Short bones
  • Flat bones
  • Irregular bones

  
• Long Bone Structures


  Diaphysis: Shaft, compact bone tissue (on outside)

  Epiphysis: Ends, spongy bone tissue

  Articular cartilage: Covers epiphyses, reduces friction

  Epiphyseal plate: Site of growth between diaphysis and epiphysis

  Medullary cavity: Center of diaphysis, red or yellow marrow

  Periosteum: Membrane around bone's outer surface

  Endosteum: Membrane that lines medullary cavity

  
• Bone Marrow


  Red marrow: Location of blood forming cells

  Yellow marrow: Mostly fat
• Compact Bone Tissue


  Osteon: Structural unit, includes lamella, lacunae, canaliculus, central canal, osteocytes

  Lamella: Rings of bone matrix

  Lacunae: Spaces between lamella

  Canaliculus: Tiny canals, transport nutrients and remove waste

  Central canal: Center of osteon, contains blood vessels

  
• Spongy (Cancellous) Bone Tissue

  Contains trabeculae, which are interconnecting rods, and spaces that contain marrow. Has no osteons.

  
• Bone Cells


  • Osteoblasts: Responsible for bone formation, repair, and remodeling

  Osteocytes: Maintain bone matrix, form from osteoblasts

  Osteoclasts: Contribute to bone repair and remodeling by removing existing bone

  
• Bone Formation


  Ossification: Formation of bone by osteoblasts

  Intramembranous ossification: Bone formation within connective tissue membranes

  Endochondral ossification: Bone formation inside hyaline cartilage

  
• Intramembranous Ossification


  Osteoblasts line up on surface of connective tissue fibers and begin depositing bone matrix to form trabeculae

  Process begins in ossification centers, trabeculae radiate out

  Trabeculae are constantly remodeled and may enlarge or be replaced by compact bone

  
• Endochondral Ossification


  Chondroblasts build a cartilage model

  2. Cartilage model calcifies

  3. Osteoblasts invade calcified cartilage, primary ossification center forms in diaphysis

  4. Secondary ossification centers form in epiphysis

  5. Original cartilage model is almost completely ossified, remaining cartilage is articular cartilage
• Bone Repair


  Broken bone causes bleeding, blood clot forms

  2. Callus forms, a fibrous network between 2 fragments

  3. Cartilage model forms first, then osteoblasts enter callus and form cancellous bone

  4. Cancellous bone is slowly remodeled to form compact and cancellous bone

  
• Bone Anatomical Terms


  Foramen: Hole

  Fossa: Depression

  Process: Projection

  Condyle: Smooth, rounded end

  Meatus: Canal-like passageway

  Tubercle: Lump of bone

  
• Axial Skeleton


  • Skull

  Vertebral column

  Thoracic cage

  
• Cranial Bones


  • Frontal bone

  Parietal bones

  Occipital bones

  Temporal bones

  Sphenoid bone

  
• Axial skeleton


  Composed of the skull, the vertebral column, and the thoracic cage

  
• Skull


  Has 22 bones divided into those of the braincase and those of the face

  
• Braincase


  • Encloses the cranial cavity, consists of 8 bones that immediately surround and protect the brain
• Face


  • Has 14 facial bones

  
• Facial bones


  • 13 are rather solidly connected to form the bulk of the face, the mandible forms a freely movable joint with the rest of the skull

  
• Middle ear


  • Has 3 auditory ossicles in each (6 total)
• Cranial bones


  • Frontal
  • Parietal
  • Occipital
  • Temporal
• Cranial bones (continued)


  • Sphenoid
  • Ethmoid

  
• Facial bones


  • Maxillae
  • Palatine
  • Zygomatic
  • Lacrimal
  • Nasal
  • Vomer
  • Inferior nasal conchae
  • Mandible
• Hyoid bone


  • Unpaired, U-shaped, not part of the skull, no direct bony attachment, provides attachment for tongue and neck muscles

  
• Vertebral column


  • Central axis of the skeleton, extends from base of skull to past the pelvis, usually 26 bones in 5 regions, has 4 major curvatures

  
• Vertebrae


  • 7 cervical
  • 12 thoracic
  • 5 lumbar
  • 1 sacrum
  • 1 coccyx
• Atlas


  • 1st vertebra, holds the head
• Axis


  • 2nd vertebra, rotates the head
• Functions of vertebral column

  • Supports body weight
  • Protects the spinal cord
  • Allows spinal nerves to exit
  • Provides site for muscle attachment
  • Provides movement of head and trunk
• Thoracic cage


  • Protects vital organs, 12 pairs of ribs, sternum, true ribs, false ribs, floating ribs
• Pectoral girdle


  • Scapula (shoulder blade), clavicle (collar bone)
• Upper limb bones


  • Humerus
  • Ulna
  • Radius
  • Carpals
  • Metacarpals