Bones, Skeletal Tissue, and Joints: ANP Exam 2 Study Guide

Bones and Skeletal Tissue

Overview of the Skeletal System

The human skeleton is a dynamic organ system composed of bones, cartilage, ligaments, and other connective tissues. It provides structural support, protection, and facilitates movement.

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

• Axial Skeleton: Composed of 80 bones, including the skull, vertebral column, and thoracic cage.

• Appendicular Skeleton: Composed of 126 bones, including the limbs and girdles (shoulder and pelvic).

Functions of the Skeletal System

• Support: Provides a framework for the body and supports soft tissues.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Serves as levers for muscles to act upon.

• Mineral Storage: Stores calcium and phosphate ions.

• Blood Cell Production: Houses red bone marrow for hematopoiesis.

• Triglyceride Storage: Yellow bone marrow stores fat.

Bone Markings and Landmarks

Bones display various surface features that serve as attachment points for muscles, ligaments, and tendons, or as passageways for nerves and blood vessels.

• Foramen: Round or oval opening through a bone (e.g., foramen magnum).

• Process: Any bony prominence (e.g., mastoid process).

• Condyle: Rounded articular projection (e.g., femoral condyles).

• Crest: Narrow, prominent ridge (e.g., iliac crest).

Bone Cells and Their Functions

• Osteogenic Cells: Stem cells found in the periosteum and endosteum; differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue; found in lacunae.

• Osteoclasts: Bone-resorbing cells; break down bone matrix; found on bone surfaces.

Bone Shapes and Examples

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

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

• Flat Bones: Thin, flattened, and usually curved (e.g., sternum, skull bones).

• Irregular Bones: Complicated shapes (e.g., vertebrae, hip bones).

• Sesamoid Bones: Form within tendons (e.g., patella).

Bone Components: Organic vs. Inorganic

• Organic Components: Include cells (osteogenic, osteoblasts, osteocytes, osteoclasts) and osteoid (collagen fibers and ground substance). Provide flexibility and tensile strength.

• Inorganic Components: Mainly hydroxyapatite (mineral salts, primarily calcium phosphate). Provide hardness and resistance to compression.

Bone Structure: Gross and Microscopic Anatomy

• Gross Anatomy:

  • Compact Bone: Dense outer layer; provides strength.

  • Spongy Bone (Cancellous): Honeycomb of trabeculae; contains red or yellow marrow.

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

  • Epiphyses: Ends of long bones; covered with articular cartilage.

  • Periosteum: Outer fibrous membrane; site of muscle attachment.

  • Endosteum: Membrane lining internal bone surfaces.

• Microscopic Anatomy:

  • Osteon (Haversian System): Structural unit of compact bone.

  • Lamellae: Concentric rings of bone matrix.

  • Central (Haversian) Canal: Contains blood vessels and nerves.

  • Lacunae: Small spaces housing osteocytes.

  • Canaliculi: Tiny canals connecting lacunae.

Ossification (Bone Formation)

• Intramembranous Ossification: Bone develops from fibrous membrane; forms flat bones (e.g., skull, clavicle).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage; forms most bones below the skull.

Types of Vertebrae: Differences and Similarities

Type	Location	Key Features
Cervical	Neck (7)	Small body, transverse foramina, bifid spinous process (except C7)
Thoracic	Upper back (12)	Articulate with ribs, heart-shaped body, long spinous process
Lumbar	Lower back (5)	Large body, short thick spinous process, no rib facets

Red and Yellow Marrow

• Red Marrow: Site of blood cell formation; found in spongy bone of flat bones and epiphyses of long bones.

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

Paranasal Sinuses

• Definition: Air-filled spaces within certain skull bones; lined with mucous membrane.

• Location: Frontal, ethmoid, sphenoid, and maxillary bones.

• Functions: Lighten skull, warm and moisten air, enhance voice resonance.

Aging and the Skeletal System

• Effects: Bone mass decreases, bones become more brittle, increased risk of osteoporosis and fractures.

• Prevention/Delay: Adequate calcium and vitamin D intake, regular weight-bearing exercise, avoiding smoking and excessive alcohol.

Fractures: Types and Recovery

• Types: Simple (closed), compound (open), comminuted, greenstick, spiral, compression, etc.

• Recovery: Involves hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling.

Sex Differences in the Skeleton

• Male Skeleton: Generally larger, heavier, with more prominent bone markings.

• Female Skeleton: Pelvis is wider and shallower for childbirth; less pronounced bone markings.

Joints (Articulations)

Functions and Classification of Joints

Joints are sites where two or more bones meet, allowing for movement and providing stability.

• Functional Classification:

  • Synarthroses: Immovable joints (e.g., sutures of the skull).

  • Amphiarthroses: Slightly movable joints (e.g., intervertebral discs).

  • Diarthroses: Freely movable joints (e.g., shoulder, knee).

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue; no joint cavity (e.g., sutures, syndesmoses).

  • Cartilaginous Joints: Bones joined by cartilage; no joint cavity (e.g., synchondroses, symphyses).

  • Synovial Joints: Bones separated by a fluid-filled joint cavity; most movable type.

Synovial (Diarthrotic) Joints: Main and Accessory Structures

• Articular Cartilage: Hyaline cartilage covering bone ends; reduces friction.

• Joint (Articular) Cavity: Space containing synovial fluid.

• Articular Capsule: Two-layered capsule enclosing the joint cavity.

• Synovial Fluid: Lubricates and nourishes articular cartilage.

• Ligaments: Reinforce and strengthen joints.

• Accessory Structures: Menisci (articular discs), bursae, and tendon sheaths reduce friction and improve fit.

Types of Movement at Synovial Joints

• Gliding: Flat bone surfaces slide over one another (e.g., intercarpal joints).

• Angular Movements: Flexion, extension, abduction, adduction, circumduction.

• Rotation: Bone turns around its own long axis (e.g., atlas and axis, shoulder).

• Special Movements: Supination, pronation, inversion, eversion, protraction, retraction, elevation, depression, opposition.

Types of Synovial Joints and Examples

Type	Movement	Example
Hinge	Flexion/Extension	Elbow, knee
Ball-and-Socket	Multiaxial	Shoulder, hip
Condylar (Ellipsoid)	Biaxial	Wrist, metacarpophalangeal joints
Pivot	Rotation	Atlas/axis, proximal radioulnar joint
Plane (Gliding)	Nonaxial	Intercarpal, intertarsal joints
Saddle	Biaxial	Thumb (carpometacarpal joint)

Knee Joint Structure

• Type: Modified hinge joint; largest and most complex synovial joint.

• Main Structures: Articular cartilage, menisci (medial and lateral), joint capsule, synovial membrane, ligaments (anterior/posterior cruciate, medial/lateral collateral), patella.

• Accessory Structures: Bursae, fat pads.

Example:

The shoulder joint is a ball-and-socket synovial joint, allowing for the greatest range of motion in the body, but is also more prone to dislocation due to its shallow socket.

Additional info: For diagrams and images of bone markings, vertebrae, and joint movements, refer to your textbook or lecture slides as visual identification is often required in lab exams.