Skeletal System Overview

The skeletal system provides the framework for the human body, supporting movement, protecting organs, and serving as a site for blood cell production. This guide covers the major bones, their locations and functions, as well as key components and tissue types found in the skeletal system.

Bones

Major Bones: Location, Description, and Function

• Appendicular Skeleton: Includes bones of the limbs and girdles that attach them to the axial skeleton.

• Axial Skeleton: Comprises the skull, vertebral column, and thoracic cage.

Upper Limb Bones

• Humerus: Upper arm bone; articulates with the scapula at the shoulder and the radius and ulna at the elbow.

• Radius and Ulna: Forearm bones; radius is lateral (thumb side), ulna is medial (pinky side).

• Carpals: Eight small bones forming the wrist.

• Metacarpals: Five bones forming the palm.

• Phalanges: Bones of the fingers; each finger has three (proximal, middle, distal), except the thumb, which has two.

  • Thumb vs. Big Toe: Thumb (pollex) has two phalanges; big toe (hallux) also has two.

  • All Other Fingers/Toes: Have three phalanges each.

Lower Limb Bones

• Femur: Thigh bone; the longest and strongest bone in the body.

• Tibia: Shin bone; larger and medial bone of the lower leg.

• Fibula: Lateral bone of the lower leg; thinner than the tibia.

• Patella: Kneecap; protects the knee joint.

• Pelvis: Includes ilium, ischium, and pubis; supports the spinal column and protects abdominal organs.

• Tarsals: Seven bones forming the ankle.

• Metatarsals: Five bones forming the foot arch.

• Phalanges: Toes; similar structure to fingers.

Axial Skeleton Bones

• Vertebral Column: Supports the body and protects the spinal cord; includes cervical, thoracic, lumbar, sacrum, and coccyx regions.

• Sternum: Breastbone; central part of the chest.

• Clavicle: Collarbone; connects the arm to the trunk.

• Scapula: Shoulder blade; provides attachment for upper limb muscles.

• Ribs: Protect thoracic organs; 12 pairs.

  • True Ribs: First 7 pairs; attach directly to the sternum.

  • False Ribs: Next 3 pairs; attach indirectly or not at all to the sternum.

  • Floating Ribs: Last 2 pairs; do not attach to the sternum.

Skeletal System Components

Description, Function, and Examples

• Cartilage: Flexible connective tissue found in joints, ear, nose, and respiratory tract; provides cushioning and support.

• Ligament: Dense connective tissue connecting bones to other bones; stabilizes joints.

• Joint: Site where two or more bones meet; allows for movement and flexibility.

• Tendon: Connects muscle to bone; transmits force to enable movement.

Upper and Lower Limbs

• Upper Limbs: Includes the humerus, radius, ulna, carpals, metacarpals, and phalanges.

• Lower Limbs: Includes the femur, tibia, fibula, tarsals, metatarsals, and phalanges.

Types and Characteristics of Skeletal Tissues

• Bone Remodeling Process: Continuous process where old bone is replaced by new bone tissue; involves osteoblasts (build bone) and osteoclasts (break down bone).

• Types of Bone Marrow:

  • Red Bone Marrow: Produces blood cells; found in flat bones and the ends of long bones.

  • Yellow Bone Marrow: Stores fat; found in the medullary cavity of long bones.

• Spongy Bone: Porous bone found at the ends of long bones and inside flat bones; contains red marrow.

• Compact Bone: Dense bone forming the outer layer of bones; provides strength and protection.

Other Skeletal System Features

• Periosteum: Membrane covering the outer surface of bones; contains nerves and blood vessels.

• Articular Cartilage: Smooth tissue covering the ends of bones in joints; reduces friction.

• Diaphysis: Shaft of a long bone; contains the medullary cavity.

• Epiphysis: End part of a long bone; contains spongy bone and red marrow.

• Long Bones: Longer than they are wide (e.g., femur, humerus).

• Short Bones: Cube-shaped (e.g., carpals, tarsals).

• Flat Bones: Thin and broad (e.g., sternum, skull bones).

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvis).

Types of Bone Fractures

• Transverse Fracture: Break is straight across the bone.

• Oblique Fracture: Break has a curved or sloped pattern.

• Comminuted Fracture: Bone is broken into several pieces.

• Greenstick Fracture: Incomplete fracture; bone bends and cracks (common in children).

Summary Table: Bone Types and Examples

Key Terms and Definitions

• Osteoblast: Cell that forms new bone tissue.

• Osteoclast: Cell that breaks down bone tissue.

• Osteocyte: Mature bone cell that maintains bone tissue.

• Medullary Cavity: Central cavity of bone shafts where yellow marrow is stored.

• Epiphyseal Plate: Growth plate; area of growing tissue near the ends of long bones in children and adolescents.

Additional info:

• Bone remodeling is regulated by hormones such as parathyroid hormone and calcitonin.

• Joints can be classified structurally (fibrous, cartilaginous, synovial) and functionally (immovable, slightly movable, freely movable).