Dem Bones Pt. II

April 15th, 7:30 AM

The adult human skeleton consists of 206 bones. There are two main functional groupings of bones. The axial skeleton includes the skull (cranium and mandible), the hyoid bone in the neck that supports tongue movement, the vertebral column that forms the middle axis of the skeleton, and the thoracic cage (ribs and sternum) which protects the inner organs of the thorax and upper abdomen. The appendicular skeleton includes the pectoral girdle (scapula and clavicle) which permits movement of the upper limbs, the upper limbs themselves (humerus, radius, ulna, wrist, and hand), the pelvic girdle (the fused illium, ischium, and pubis bones form the two coxal bones), and the lower limbs (femur, tibia, fibula, and the foot).

Bone Microscopic Structure

- Composed of bone tissue, cartilage, ligaments, tendons, vasculature, and nervous tissue

- Bone tissue is a collection of specialized cells (osteoblasts, osteoclasts, osteocytes), organic extracellular matrix proteins (collagen and proteoglycans), and inorganic salt crystals

- Classifications of bone tissue:

- Compact bone: Bone tissue with a tightly packed microstructure arranged into rings, also called cortical or lamellar bone. Compact bone gives bones their stiffness; it is heavy and brittle.

- Spongy bone: Bone tissue with a porous microstructure, also called cancellous or trabecular bone. It consists of branching bone structures called trabeculae, reduces the weight and brittleness of bone, and is found at the ends of bone where forces are high.

Four Main Shapes of Bones

1. Long bones are significantly larger in one direction than in the other two; i.e. the femur

2. Short bones are a similar length in all directions, i.e. the carpal bones of the wrist or tarsal bones of the ankle

3. Flat bones are flat and plate-like, i.e. the bones of the skull

4. Irregular bones are not regular or systematic in shape like the bones of the hip/pelvic girdle or the vertebral column

Components of Long Bones

- Diaphysis/shaft

- Epiphyses at the bone ends

- Metaphysis, the transitional area between the diaphysis and epiphysis

Terms to know:

Medullary cavity- Houses yellow bone marrow in adults and runs throughout the diaphysis

Yellow bone marrow- Rich in fat, found in the interior of the bone cavity

Epiphyseal plate- The junction between the epiphysis and metaphysis in children, a layer of cartilage which allows bone to lengthen (growth plate)

Epiphyseal line- Found in adults whose epiphyseal plate has been entirely calcified

Articular cartilage- The area of hyaline cartilage left in adults, found on the outer edge of the epiphysis and functions to cushion and reduce friction between bones

Articulations (Joints)

Synarthrotic articulations- Immovable articulations joined with fibrous connective tissue

Amphiarthrotic articulations- Have limited motion and are held in place with fibrocartilage or fibrous connective tissue

Diarthrotic articulations- Have a wide range of motion, are said to be freely moveable, and have a joint cavity which consists of a joint capsule surrounding the joint and a synovial membrane inside it. Further grouped into several types:

- Nonaxial joints: Do not have a pivot or axis of movement

- Unaxial/Monoaxial joints: Have one axis of movement, i.e. hinge and pivot joints. Have protrusions that fit into a corresponding depression.

- Biaxial joints: Have two axes of movement, i.e. saddle joints (thumb) or ellipsoid/condylar joints

- Triaxial joints: Three axes of movement, i.e. ball-and-socket joints

End: 8:30 AM

#capacitybuilding #seniorproject #anatomy #skeletalsystem #physiology