Skeletal System Overview

Introduction to the Skeletal System

The skeletal system is a fundamental organ system in the human body, providing structure, protection, and support for movement. It is composed primarily of bone tissue and associated connective tissues.

• Type of Tissue: The skeletal system is mainly made up of bone tissue, a specialized form of connective tissue.

• Functions: Protection of vital organs, support for body structure, facilitation of movement, mineral storage (especially calcium and phosphorus), and blood cell production (hematopoiesis).

Divisions and Structure of the Skeletal System

Major Divisions

The human skeleton is divided into two main parts:

• Axial Skeleton: Includes the skull, vertebral column, and rib cage. Provides central support and protects internal organs.

• Appendicular Skeleton: Includes the limbs and girdles (pectoral and pelvic). Facilitates movement and interaction with the environment.

Total Number of Bones: The adult human skeleton contains 206 bones.

Classification of Bones

Bones are classified based on their shapes and functions:

• Long Bones: Longer than they are wide; found in arms and legs (e.g., femur, humerus).

• Short Bones: Approximately equal in length and width; found in wrists and ankles (e.g., carpals, tarsals).

• Flat Bones: Thin and broad; provide protection (e.g., skull, sternum, ribs).

• Irregular Bones: Complex shapes; do not fit other categories (e.g., vertebrae, some facial bones).

Surface Markings on Bones

Surface markings are features on bones that serve as attachment points for muscles, ligaments, and tendons, or as passageways for nerves and blood vessels.

• Examples: Foramina (holes), processes (projections), fossae (depressions).

Parts of a Long Bone

Long bones have distinct structural regions:

• Diaphysis: The shaft or central part of the bone.

• Epiphysis: The ends of the bone, usually wider than the shaft.

• Metaphysis: The region between diaphysis and epiphysis, containing the growth plate.

• Medullary Cavity: Central cavity containing bone marrow.

• Periosteum: Outer fibrous covering of the bone.

Vertebral Column and Ribs

Structure and Function of the Vertebral Column

The vertebral column (spine) supports the body and protects the spinal cord.

• Regions: Cervical (neck), thoracic (upper back), lumbar (lower back), sacral, and coccygeal.

• Top Two Vertebrae: Atlas (C1) and Axis (C2) allow for head movement.

• Function: Protects the spinal cord, supports the head, and provides attachment for ribs and muscles.

• Structural Features: Vertebral body, vertebral arch, spinous process, transverse process.

• Vertebral Foramen: The central opening through which the spinal cord passes.

Classification and Articulation of Ribs

Ribs are classified based on their attachment to the sternum:

• True Ribs (1-7): Directly attached to the sternum via costal cartilage.

• False Ribs (8-12): Indirectly attached or not attached to the sternum.

• Floating Ribs (11-12): Do not attach to the sternum.

• Articulation: Ribs articulate posteriorly with thoracic vertebrae and anteriorly with the sternum (for true ribs).

Developmental Curves of the Spine

The vertebral column develops curves for balance and support:

• Primary Curves: Thoracic and sacral curves are present at birth.

• Secondary Curves: Cervical and lumbar curves develop after birth as the child begins to hold up the head and walk.

Bone Growth and Development

Types of Bone Growth

Bones grow in length and width through two main processes:

• Longitudinal Growth: Occurs at the epiphyseal (growth) plates.

• Appositional Growth: Increase in bone thickness.

Cartilage vs. Bone

Cartilage and bone are both connective tissues but differ in structure and function:

• Cartilage: Flexible, avascular tissue; provides cushioning and support (e.g., articular cartilage in joints).

• Bone: Rigid, vascular tissue; provides structural support and protection.

Bone Cells and Their Roles

Bone tissue contains specialized cells:

• Osteocytes: Mature bone cells that maintain bone tissue.

• Osteoblasts: Cells responsible for bone formation.

• Osteoclasts: Cells that break down bone tissue (bone resorption).

Major Bones and Bone Features

Specific Bones of the Adult Skeleton

Key bones to identify include:

• Pelvis: Composed of ilium, ischium, and pubis.

• Pectoral Girdle: Includes clavicle and scapula.

• Sternum: Central bone of the chest.

Fractures

Fractures are breaks in bone continuity. Types include:

• Simple (Closed) Fracture: Bone breaks but does not pierce the skin.

• Compound (Open) Fracture: Bone breaks and pierces the skin.

• Comminuted Fracture: Bone is shattered into several pieces.

• Greenstick Fracture: Incomplete break, common in children.

Joints and Movements

Types of Joints

Joints (articulations) are classified by structure and movement:

• Fibrous Joints: Immovable (e.g., sutures in the skull).

• Cartilaginous Joints: Slightly movable (e.g., intervertebral discs).

• Synovial Joints: Freely movable (e.g., shoulder, knee).

Specific Movements at Joints

Joints allow for various movements:

• Flexion: Decreasing the angle between bones.

• Extension: Increasing the angle between bones.

• Abduction: Moving a limb away from the midline.

• Adduction: Moving a limb toward the midline.

• Rotation: Movement around an axis.

Structures of Joints

Different structures within joints serve specific functions:

• Ligaments: Connect bone to bone, providing stability.

• Tendons: Connect muscle to bone, enabling movement.

• Synovial Membrane: Secretes synovial fluid for lubrication.

Summary Table: Bone Types and Examples

Key Equations and Concepts

• Bone Remodeling Equation:

• Calcium Homeostasis: Bones act as a reservoir for calcium, regulated by hormones such as parathyroid hormone (PTH) and calcitonin.

Additional info: Some content was inferred and expanded for completeness, including definitions, examples, and academic context for bone types, joint movements, and bone cell functions.