ANS250 Lecture 5 Skeletal System 1

The Skeletal System

Objectives

• Identify the major bones of the skeletal system.

• Distinguish between the axial skeleton and the appendicular skeleton.

• Explain the function and structure of bone.

• Summarize how bones develop and elongate.

• List three classes of joints, describe the action of each and give an example of each.

The Skeleton

• Acts as a support system for organisms:

  • Single-celled organisms: Support from the cell membrane and cytoskeleton.

  • Multicellular animals: Support from a skeleton.

• Types of animal skeletons:

  • Exoskeleton: An outside skeleton (e.g., arthropods).

  • Endoskeleton: An inside skeleton (e.g., vertebrates).

Bone Terminology

• Common terms associated with bones include:

  • OS: Example - Os penis.

  • Base, Body, Cranial, Dorsal, Ventral, Urethral groove.

  • Apex: The tip or pointed end of a structure.

Bone Characteristics

• Bone is the second hardest natural substance in the body, with enamel being harder.

• Bone is a vital living tissue with excellent repair capabilities.

• Composed of:

  • Osteoblasts (cells that form bone).

  • Matrix: Hard substance surrounding bone cells; composed of calcium and phosphate salts that harden through ossification.

Bone Cells – MUST KNOWS

• Osteoblasts:

  • Secrete soft matrix composed of collagen fibers and proteins.

  • Involved in ossification with hydroxyapatite (calcium and phosphate).

  • Some become trapped in lacunae.

• Osteocytes:

  • Osteoblasts surrounded by bone, connected via canaliculi.

  • Can revert to osteoblasts for repair.

• Osteoclasts:

  • Break down bone for remodeling.

  • Allow for calcium withdrawal.

Growth Plates

• Physis: The growth plates where bone elongation occurs.

Functions of Bone - Know

• Support: Provides structural integrity.

• Protection: Encases vital organs.

• Leverage: Facilitates movement.

• Storage: Storage of calcium, essential for muscle contraction and blood clotting.

  • Calcitonin: Prevents hypercalcemia by promoting calcium deposition in bones.

  • Parathyroid hormone: Prevents hypocalcemia by promoting calcium resorption from bones.

• Blood cell formation: Hematopoiesis occurs in red bone marrow.

Long Bone Structure

• Essential components include:

  • Epiphysis: Ends of long bones.

  • Articular cartilage: Covers joint surfaces.

  • Spongy bone: Contains red marrow cavities.

  • Compact bone: Dense and strong; forms the shaft (diaphysis).

  • Medullary cavity: Contains yellow marrow.

  • Endosteum: Lining of the medullary cavity.

  • Periosteum: Outer fibrous covering of the bone.

Bone Structure Comparison

• Compact Bone:

  • Also known as cortical bone, about 80% of skeletal mass.

  • Provides strength and rigidity.

• Cancellous Bone:

  • Also known as trabecular/spongy bone, lighter and less dense.

  • Representing 20% of skeletal mass but 80% of bone volume.

  • Contains red and yellow marrow, involved in blood cell generation.

Common Bone Features - Know

• Articular surfaces: Smooth areas of bone where joints form; covered with hyaline cartilage.

  • Condyle & Head: Types of articular surfaces found on bones.

• Processes: Projections on bones where muscles and tendons attach.

• Holes and Depressed Areas: Foramina (holes for blood vessels/nerves) and fossae (depressions for muscle/tendon accommodation).

Axial Skeleton - Know

• Major components include:

  • Skull: External and internal bones, bones of the ear, hyoid bone.

  • Spinal column: Cervical, thoracic, lumbar, sacral, coccygeal vertebrae.

  • Ribs and sternum: Protect thoracic cavity contents.

Appendicular Skeleton

• Comprises of:

  • Thoracic limb: Scapula, humerus, radius, ulna, carpal bones, metacarpals, phalanges.

  • Pelvic limb: Pelvis, femur, patella, tibia, fibula, tarsal bones, metatarsals, phalanges.

Joints - Know Types and Functions

• Joints are classified into three categories:

  • Fibrous Joints (Immovable): E.g., skull sutures.

  • Cartilaginous Joints (Semi-movable): E.g., intervertebral disks.

  • Synovial Joints (Freely movable): E.g., knee, hip joints.

Synovial Joint Characteristics

• Articular surfaces: Covered by articular cartilage and enclosed in a joint capsule filled with synovial fluid.

• Ligaments: Stabilizing structures connecting bones.

Movements of Synovial Joints

• Include:

  • Flexion & Extension: Decrease/increase angle.

  • Abduction & Adduction: Movement away/toward the body midline.

  • Rotation & Circumduction: Rotation around an axis and circular movement.