Skeletal System

• Functions of bones


  • Support
  • Protection
  • Allow movement
  • Storage
  • Blood cell formation
• Compact bone


  • Dense and looks smooth and homogenous
• Spongy bone


  • Has a spiky, open appearance like sponge
• Types of bones by shape

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


  Typically longer than they are wide, have a shaft with enlarged ends, mostly compact bone but also contain spongy bone at the ends
• Flat bones


  Thin, flattened, and usually curved, have two thin layers of compact bone sandwiching a layer of spongy bone between them
• Short bones


  Generally cube-shaped and contain mostly spongy bone with an outer layer of compact bone
• Irregular bones


  Bones that do not fit one of the preceding categories, like the vertebrae
• Structures of a long bone

  • Diaphysis
  • Periosteum
  • Perforating fibers
  • Epiphyses
  • Articular cartilage
  • Epiphyseal line
  • Epiphyseal plate
  • Endosteum
  • Medullary cavity
• Diaphysis

  The shaft of a long bone, composed of compact bone
• Periosteum

  A connective tissue membrane that covers and protects the diaphysis
• Perforating fibers


  Connective tissue fibers that secure the periosteum to the underlying bone
• Epiphyses

  The ends of long bones, each consisting of a thin layer of compact bone enclosing an area filled with spongy bone
• Articular cartilage

  Glassy hyaline cartilage that provides a smooth surface to decrease friction at the joint
• Epiphyseal line

  A thin line of bony tissue spanning the epiphyses, a remnant of the epiphyseal plate
• Epiphyseal plate

  A flat plate of hyaline cartilage in young, growing bone that causes lengthwise growth
• Endosteum

  A delicate connective tissue that covers the inner bony surface of the shaft
• Medullary cavity

  The cavity of the shaft, a storage area for red marrow in infants and yellow marrow in adults
• Bone markings reveal where muscles, tendons, and ligaments attach and where blood vessels and nerves pass
• Osteon


  The structural and functional unit of compact bone, consisting of a central canal and surrounding matrix rings
• Canaliculi


  Tiny canals that radiate outward from the central canals to connect all the bone cells to the nutrient supply and waste removal
• Perforating canals


  Canals that run in the compact bone at right angles to the shaft and central canals, completing the communication pathway from the outside of the bone to its interior
• Bone is one of the hardest materials in the body, and has a remarkable ability to resist tension and other forces
• The calcium salts deposited in the matrix give bone its hardness, while the organic parts (especially the collagen fibers) provide flexibility and tensile strength
• Ossification


  The process of bone formation, involving covering the hyaline cartilage model with bone matrix and then digesting away the enclosed cartilage
• Bone remodeling


  The process of bone being remodeled in response to changes in calcium levels in the blood and the pull of gravity and muscles on the skeleton
• Rickets is a disease of children in which the bones fail to calcify, causing the weight-bearing bones to become bowed
• Fracture repair


  1. Hematoma formation

  2. Fibrocartilage callus formation

  3. Bony callus formation

  4. Bone remodeling
• Bones of the axial skeleton

  • Skull
  • Hyoid bone
  • Auditory ossicles
  • Ribs
  • Sternum
• Cranium


  The boxlike structure that encloses and protects the brain, composed of 8 large flat bones
• Bones of the cranium

  • Frontal
  • Parietal
  • Temporal
  • Occipital
  • Sphenoid
  • Ethmoid
• Frontal bone


  Forms the forehead, bony projections under the eyebrows, and the superior part of each eye's orbit
• Parietal bones


  Form most of the superior and lateral walls of the cranium, meet at the sagittal suture and form the coronal suture with the frontal bone
• Temporal bones

  Lie inferior to the parietal bones, contain the external auditory meatus, styloid process, zygomatic process, and mastoid process
• Occipital bone

  The most posterior bone of the cranium, forms the floor and back wall of the skull, contains the foramen magnum
• Sphenoid bone

  Spans the width of the skull, forms part of the floor of the cranial cavity, contains the sella turcica, foramen ovale, optic canal, and superior orbital fissure
• Ethmoid bone

  Lies anterior to the sphenoid, forms the roof of the nasal cavity and part of the medial walls of the orbits, projects the crista galli
• Parietal bones


  • Join anteriorly at the lambdoid suture
  • Have a large opening, the foramen magnum, that surrounds the lower part of the brain and allows the spinal cord to connect with the brain
  • Have rockerlike occipital condyles which rest on the first vertebra of the spinal column
• Sphenoid bone

  • Spans the width of the skull and forms part of the floor of the cranial cavity
  • Has a small depression, the sella turcica, which holds the pituitary gland in place
  • Has the foramen ovale, a large oval opening that allows fibers of cranial nerve V to pass to the chewing muscles of the lower jaw
  • Has the optic canal and superior orbital fissure which allow the optic nerve and cranial nerves controlling eye movements to pass
  • Is riddled with air cavities, the sphenoidal sinuses
• Ethmoid bone

  • Lies anterior to the sphenoid and forms the roof of the nasal cavity and part of the medial walls of the orbits
  • Has the crista galli, which the outermost covering of the brain attaches to
  • Has the cribriform plates, which allow nerve fibers carrying impulses from the olfactory receptors of the nose to reach the brain
  • Has the superior nasal conchae and middle nasal conchae, which form part of the lateral walls of the nasal cavity