Biology: Bone Structure and Cells

Bone Structure

• Spongy bone consists of interconnecting rods or plates of bone called trabeculae
• Compact bone (Cortical Bone) is a solid, outer layer surrounding each bone

Bone Cells

• There are three types of bone cells:
  • Osteoblasts: bone-building cells
  • Osteocytes: mature bone cells
  • Osteoclasts: break down and resorb bone tissue

Osteon

• Functional unit of compact bone
• Composed of concentric rings of matrix, which surround a central tunnel and contain osteocytes
• Central canal: the "bull's eye" of the target, circular target resembled by the osteon

Long Bone Structure

• Traditional model for overall bone structure
• Outer compact bone surfaces and spongy centers
• Centers of ossification: locations in the membrane where intramembranous ossification begins
• Fontanels (Soft Spots): larger, membrane-covered spaces between the developing skull bones that have not yet been ossified
• Diaphysis: center portion of the bone, composed of primarily compact bone tissue
• Epiphyses: ends of a long bone, mostly spongy bone with an outer layer of compact bone
• Medullary Cavity: hollow center surrounded by the diaphysis
• Endochondral Ossification: cartilage model
• Epiphyseal Plate (Growth Plate): located between the epiphysis and the diaphysis, where growth in bone length occurs
• Epiphyseal Line: when bone stops growing in length, the epiphyseal plate becomes ossified

Skull Bones

• Parietal Bones:
  • Connected to the occipital bone by the lambdoid suture
  • Along with the temporal bones, make up the majority of the lateral portion of the skull
• Temporal Bones:
  • Connected to the skull by the squamous sutures
  • Subdivided into three main regions:
    • Squamous part: meets the parietal bone
    • Tympanic part: has the prominent external auditory canal
    • Petrous part: extends inward toward the center of the skull, houses the middle and inner ears

Other Bones

• Occipital Bone: makes up the majority of the skull's posterior wall and base
• Sphenoid Bone: a single bone that extends completely across the skull
• Hyoid Bone: important for speech and swallowing
• Vertebral Column: performs five major functions, consisting of 26 bones (vertebrae) divided into five regions

Vertebral Column

• General Features of the Vertebrae:
  • Each vertebra consists of a body, a vertebral arch, and various processes
  • Vertebral Body: solid bony disk of each vertebra, supports the body's weight
  • Vertebral Arch: along with the body, protects the spinal cord
  • Vertebral Foramen: occupied by the spinal cord in a living person
  • Vertebral Canal: contains the entire spinal cord and cauda equina
  • Transverse Process: extend laterally from each side of the arch between the lamina and the pedicle
  • Spinous Process: lies at the junction between the two laminae
  • Intervertebral Foramina: locations where two vertebrae meet
  • Synchondroses: contain hyaline cartilage
  • Symphyses: contain fibrocartilage

Joints

• Synovial Joints: contain synovial fluid and allow considerable movement between articulating bones
• Articular Cartilage: thin layer of hyaline cartilage covering the articular surfaces of bones within synovial joints
• Meniscus: flat pad of fibrocartilage, type of articular disk that only partially spans the synovial cavity
• Joint Cavity: space around the articular surfaces of the bones in a synovial joint, filled with synovial fluid and surrounded by a joint capsule
• Fibrous Capsule: outer layer of the joint capsule, consists of dense irregular connective tissues
• Synovial Membrane: inner layer of the joint capsule, lines the joint cavity, except over the articular cartilage and articular disks
• Synovial Fluid: viscous lubricating film that covers the surfaces of a joint
• Bursa: extended as pocket or sac by the synovial membrane
• Bursitis: inflammation of a bursa, may cause considerable pain around the joint and restrict movement
• Types of Synovial Joints:
  • Plane
  • Saddle
  • Hinge
  • Pivot
  • Ball-and-socket
  • Ellipsoid