Skeletal System: Bone Structure

Bone Tissue

• Main tissue of the skeleton, composed of bone cells within a collagen and calcium salt matrix.
• Extremely strong under compression forces; designed to be both strong and lightweight.
• Compact bone is dense, found in long bones; spongy bone is lighter, located in areas like the pelvis and femur head.

Cartilage

• Hard yet flexible tissue made up of chondrocytes in an organic matrix of collagen fibrils.
• Can stretch elastically and withstands compressive forces, serving as an effective shock absorber.
• Types of cartilage:
  • Hyaline cartilage: Located at bone ends, found in the nose, airways, and parts of the ear.
  • White fibrous cartilage: Contains densely packed collagen, providing high tensile strength, situated in joints and between vertebrae.

Tendons and Ligaments

• Tendons: Composed mainly of white fibrous tissue, ideal for connecting muscles to bones; relatively inelastic.
• Ligaments: Hold bones together, composed of yellow elastic tissue, allowing for elastic movement around joints while maintaining alignment.

Joint Structure and Function

• Joints are lined with rubbery cartilage to prevent bone wear from friction and facilitate smooth movement.
• Synovial fluid acts as a lubricant in mobile joints, ensuring easy movement by filling the joint cavity.
• Joint types vary in structure:
  • Ball and socket joints (e.g., hip, shoulder) allow for extensive movement.
  • Hinge joints (e.g., knee) restrict movement.

Muscle Movement Mechanics

• Movement occurs through muscle contractions on bones; each skeletal muscle connects two bones via tendons.
• Muscles operate in antagonistic pairs: one muscle extends a joint (extensors), while the other flexes it (flexors).
• Muscles relax without applying force, returning to their original shape.

Muscle Cell Structure

• Skeletal muscle fibers: Long, multinucleate bundles, with membranes called sarcolemma.
• Transverse (T) tubules spread electrical impulses within muscle fibers.
• Sarcoplasmic reticulum stores and releases calcium ions necessary for muscle contractions.
• Muscle fibers contain many mitochondria for ATP production and specialized organelles called myofibrils for contraction.

Myofibril Structure

• Comprised of thick (myosin) and thin (actin) myofilaments, which slide past each other during contraction.
• Visible alternating dark (A-bands with myosin and actin) and light (I-bands with actin) bands under an electron microscope.
• Made of repeating units known as sarcomeres, characterized by Z-lines marking the ends and M-lines indicating the middle of myosin filaments.
• H-zone present within sarcomeres contains only myosin filaments.

This quiz explores the structure and function of bone within the skeletal system. You will learn about the types of bone, their properties, and how they support the body. Delve into the differences between compact and spongy bone and discover the role of collagen and calcium in bone composition.