Skeletons

  • Three types of skeletons:
    • Hydrostatic skeleton
    • Exoskeleton
    • Endoskeleton
  • Sponges have spicules that support their body and can deter predators, they can be composed of calcium carbonate, silica, or spongin
  • Hydrostatic Skeleton: Body cavity has a fixed volume which changes shape when muscles contract
  • Calcium carbonate: Invertebrates
  • Calcium phosphate : Vertebrates
  • Chitin: Arthropods
  • Sclerotin: Insects
  • Mollusc shells are formed by the mantle and are composed of the outer (prismatic) and inner (nacreous) layers
  • Cuttlefish have a calcium carbonate cuttlebone
  • Arthropod exoskeleton: Secreted from the hypodermis
    • Outer epicuticle of protien lipid for waterproofing
    • Internal procuticle of chitin, N-acetylglucosamine, and sclerotin
    • Articulation is from apodemes which are attached to the skeletal muscles
  • Endoskeletons:
    • Ossicular skeletons: Found in echinoderms, made up of connected plates of calcium carbonate and covered with the epidermis
    • Bony skeletons: Found in vertebrates, composed of osteocytes, in a matrix of fibres of collagen and ground substance of calcium carbonate. Bones are units called osteons.
  • Bone is constantly changed by osteoclasts which removes bone and osteoblasts which adds bones
  • Development of bones:
    • Intramembranous bone forms in the dermis of the skin from osteoblasts adding bone to collagen. Ex. flat bones in the skull, some bones in the jaw
    • Endochondral bones form from small cartilage pieces that are shaped roughly like the bones they become, bone is added to the outside and the cartilage is calcified
  • Early vertebrates just had a cartilaginous cranium and very basic vertebrae.
  • Sharks and rays have a complete cartilaginous skeleton
  • Movement is produced by muscles attached to bone acting around joints
  • Types of joints:
    • Synarthroses: Immovable joints, ex between skull bones
    • Amphiarthroses: Slightly movable joints, ex. between vertebrae
    • Diarthroses: Freely moveable ex. synovial joints
  • Types of synovial joints:
    • Hinge: One plane of movement ex. knee, elbow
    • Ball and socket: Multiple planes of movement, including twisting ex. shoulder, hip
    • Gliding: ex. carpals in wrist
    • Combination: Characteristics of multiple types of joints ex. jaw (gliding and hinge)