Biology Quiz: The Skeletal System

Skeletal System

• The skeletal system is a rigid or semi-rigid structure that supports the soft tissues of an animal's body and provides leverage for muscular action.
• In vertebrates, the skeleton is known as the endoskeleton and is formed within the body.

Types of Skeletons

• Hydrostatic skeleton: the most primitive form of skeletal structure, found in animals such as jellyfish and worms, that consists of layers of muscle around a fluid-filled body cavity.
• Exoskeleton: a hard covering on the outside of organisms such as crustaceans, insects, turtles, and armadillos that provides support and protection.
• Endoskeleton: the internal skeleton of an animal, especially of a vertebrate, consisting of cartilage or a combination of cartilage and bone.

Human Skeleton

• The human skeleton consists of 206 bones.
• Divided into two main parts: axial skeleton (80 bones) and appendicular skeleton (126 bones).
• Axial skeleton: supports the axis, or trunk, of the body, and consists of the skull, backbone, and rib cage.
• Appendicular skeleton: supports the paired appendages, and consists of bones of the shoulder girdle, upper limbs, pelvic girdle, and lower limbs.

Joints

• A joint is the place where bones meet.
• Three types of joints according to the amount of movement they allow:
  • Immovable joints (fixed joints): do not allow movement, example: suture joints in the skull.
  • Slightly movable joints (semifixed joints): allow slight movement, example: sacroiliac joint.
  • Movable joints: provide flexibility.

Bone Tissues

• Bone tissues are served by blood vessels and nerves.
• Bone cells live in a matrix of flexible protein fibers and hard calcium salts.
• Three types of bone cells:
  • Osteocytes: mature bone cells.
  • Osteoblasts: synthesize the organic components of bone.
  • Osteoclasts: responsible for the removal of bony matrix.

Bone Disorders

• Lower-back pain: persistent pain in part of the back.
• Arthritis: a medical condition affecting a joint or joints, causing pain, swelling, and stiffness.
• Osteoporosis: a disease occurring especially in women after the menopause, in which the bones become very porous, break easily, and heal slowly.
• Scoliosis: an excessive sideways curvature of the human spine.

Treatment for Bone Injuries

• The treatment of broken bones involves two steps:
  • Realigning the bone: sometimes traction must be used to align the broken parts.
  • Immobilizing the bone: use of splint or cast, plates, rods, and/or screws.
• Bone cells then build new bone and repair the break.
• Severely injured or diseased bone is beyond repair and must be replaced.