skeletal system

Learning Objectives

  1. List the bones of the axial skeleton and label important landmarks on selected bones.

  2. List the bones of the appendicular skeleton and label important landmarks on selected bones.

  3. List the main types and functions of joints and describe the types of joint movement.

Skeletal System Functions

The functions of the skeletal system include:

  • Support: Provides a framework for the body.

  • Protection: Protects vital organs.

  • Movement and Anchorage: Facilitates movement by serving as attachment points for muscles.

  • Mineral Storage: Stores minerals, particularly calcium and phosphorus.

  • Hematopoiesis: The formation of blood cells occurs in the bone marrow, which is found in certain bones like flat bones, long bones, and certain irregular bones.

Introduction to the Skeletal System

The skeletal system comprises the following components:

  • Bones

  • Joints

  • Cartilage

  • Ligaments

Bone is generally made harder through minerals, primarily calcium and phosphorus, which are abundant in the nonliving material that constitutes bone.

Sizes and Shapes of Bones

Bones come in many sizes and shapes, which are designed to serve specific functions.

Two Types of Bone (Osseous Tissue)

  1. Compact Bone (Hard)

    • Composed of Osteons (the structural unit of compact bone).

    • Commonly found in the shafts of long bones.

  2. Spongy Bone (Soft)

    • Contains Trabecular Plates which resemble a honeycomb or Swiss cheese structure.

    • Contains Bone Marrow, where hematopoiesis occurs.

    • Contains collagen fibers that provide flexibility.

Long Bones

Long bones feature several key structures:

  • Diaphysis: The shaft of the bone.

  • Epiphysis: The end part of the long bone.

  • Epiphyseal disc (Growth plate): A band of cartilage that facilitates the growth of long bones.

  • Medullary Cavity: The center of the diaphysis, containing yellow marrow primarily for fat storage.

  • Periosteum: A dense layer of vascular connective tissue enveloping the bones except at the surfaces of joints.

  • Articular Cartilage: Covers the ends of bones at joints.

Blood vessels travel through the Haversian canals in compact bone, which support nutrient delivery and bone maintenance. Bone remodeling, growth, and repair are important functions involving the medullary canal and periosteum.

Structure and Formation of Bone

  • Osteocytes: Mature bone cells responsible for maintaining bone tissue.

  • Organic Material (35%): Provides flexibility; includes collagen.

  • Inorganic Material (65%): Provides hardness and durability; includes high amounts of calcium and phosphorus that contribute to the strength of bones even post-mortem.

Growth of Bones

Bone growth occurs mainly through ossification, where the cartilage is replaced with bone material.

  • Osteoblasts: Cells that deposit new bone.

  • Osteoclasts: Large cells that secrete enzymes to break down bone tissue.

  • Bone growth stops after all epiphyseal cartilage is ossified. Female growth concludes around age 18, while males typically grow until age 20-21.

  • Hormones like estrogen and testosterone influence both the bone growth process and the overall height of the individual.

Axial Skeleton

The axial skeleton is composed of the following:

  • 22 bones of the skull

    • 14 facial bones

  • Spinal column (vertebra), which consists of:

    • Cervical: 7 vertebrae

    • Thoracic: 12 vertebrae

    • Lumbar: 5 vertebrae

    • Sacrum: 5 fused bones

    • Coccyx: 4 fused bones

  • Ribs: 12 pairs, along with the sternum and the hyoid bone.

Appendicular Skeleton

The appendicular skeleton consists of the bones of the upper and lower extremities:

Upper Extremities

  • Shoulder Girdle: Composed of 2 clavicles and 2 scapulae.

  • Arm:

    • Humerus

    • Radius

    • Ulna

  • Hand: Composed of carpals, metacarpals, and phalanges (fingers).

Lower Extremities

  • Pelvic Girdle: Comprised of ilium, ischium, and pubis.

  • Upper Leg: Femur.

  • Lower Leg: Tibia, fibula, and patella.

  • Ankle: 7 tarsal bones.

  • Foot: Composed of metatarsals and phalanges (toes).

Joints (Articulations)

Joints are points of contact between two bones. They can be categorized based on their movement:

  1. Diarthroses (Movable) Joints

  2. Amphiarthroses (Partially Movable) Joints

  3. Synarthroses (Immovable) Joints

Types of Joints

  • Diarthroses: Freely movable joints, which include:

    • Ball-and-Socket Joints: Shoulder, hip

    • Hinge Joints: Knees, elbows, fingers

    • Pivot Joints: Radius and ulna

    • Gliding Joints: Vertebrae

  • Amphiarthroses: Slightly movable joints; cartilage connects the articular surfaces (e.g., ribs to the spine).

  • Synarthroses: Fibrous joints that are immovable (e.g., sutures in the skull).

Types of Motion

  • Flexion: Decreases the angle between two bones.

  • Extension: Increases the angle between two bones.

  • Abduction: Movement away from the midline.

  • Adduction: Movement toward the midline.

  • Circumduction: A circular movement combining flexion, extension, abduction, and adduction.

  • Supination: Palm up and forward.

  • Pronation: Palm down and backward.

  • Rotation: Movement around a central axis.

Disorders of the Bones and Joints

  • Fracture Types:

    • Greenstick

    • Closed/Simple

    • Open/Compound

    • Comminuted

  • Repairing Fractures: Involves closed reduction, open reduction, and traction.

Aging of the Bones and Joints

As individuals age:

  • Bone mass and density decline.

  • External surfaces of bones may thicken.

  • Intervertebral cartilage disks shrink leading to changes in balance and mobility.

  • An increase in rigidity and a decrease in flexibility is common, often leading to a fear of falling.

  • Significant bone loss may occur in women after menopause.

Other Bone and Joint Injuries

Injuries can include:

  • Whiplash: Neck injury often from sudden movement (e.g., car accident).

  • Dislocation: Bone displacement from its normal position.

  • Sprain: Ligament injury causing pain and swelling.

  • Hammer Toe: Deformation of the toe due to abnormal pressure.

RICE Treatment:

  • Rest

  • Ice

  • Compression

  • Elevation

Diseases of the Bones

  • Arthritis: Two types include rheumatoid arthritis and osteoarthritis.

  • Gout: Caused by high uric acid levels, usually affecting the big toe.

  • Rickets: A vitamin D deficiency in children leads to bone pain and deformity.

  • Osteoporosis: Characterized by low bone mass and structural deterioration.

  • Osteomyelitis: Bone infection.

  • Osteosarcoma: Bone cancer that often requires amputation of the affected limb.

Abnormal Curvatures of the Spine

Abnormal spinal curvatures can include:

  • Kyphosis: Hunchback condition.

  • Lordosis: Swayback condition.

  • Scoliosis: Lateral curvature of the spine, which may impact respiratory function.

Other Disorders

  • Osteoporosis: Characterized by low density leading to fractures.

  • Osteomyelitis: Infection within the bone leading to inflammation.

  • Osteosarcoma: A malignant bone cancer requiring aggressive treatment.