Skeletal System

Bones: An Overview

The skeletal system provides the framework for the body, supporting and protecting organs, enabling movement, and serving as a reservoir for minerals and site for blood cell formation.

• Support: Bones form the rigid structure that supports the body.

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

• Allow Movement: Bones act as levers for muscles to produce movement.

• Storage: Bones store minerals such as calcium and phosphorus; energy is stored in bone marrow.

• Blood Cell Formation: Hematopoiesis occurs in red bone marrow.

Classification of Bones

Bones are classified by shape and structure, which relate to their function.

• Compact Bone: Dense and strong, forms the outer layer of bones.

• Spongy Bone: Porous, found at the ends of long bones and inside flat bones.

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

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

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

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

Structure of Bones

Bones have distinct anatomical regions and features.

• Diaphysis: Shaft of a long bone.

• Epiphysis: Ends of a long bone.

• Epiphyseal Line/Plate: Site of bone growth in length.

• Periosteum: Outer fibrous covering.

• Sharpey’s Fibers: Collagen fibers anchoring periosteum to bone.

• Endosteum: Lining of the medullary cavity.

• Medullary Cavity: Central cavity containing bone marrow.

• Bone Markings: Include projections, processes, grooves, fossae, and foramina for muscle attachment and passage of nerves/vessels.

Microscopic Anatomy of Bone

Bone tissue is organized into structural units for strength and nutrient delivery.

• Osteocyte: Mature bone cell.

• Lacunae: Small cavities containing osteocytes.

• Lamellae: Layers of bone matrix.

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

• Osteon: Structural unit of compact bone.

• Canaliculi: Tiny canals connecting osteocytes.

Bone Development and Growth

Bones develop through ossification and grow in length and thickness during childhood and adolescence.

• Ossification: Process of bone formation; includes endochondral (from cartilage) and membranous (from membrane) ossification.

• Osteoblasts: Cells that build bone.

• Growth at Epiphyseal Plate: Interstitial growth increases bone length.

• Growth in Bone Thickness: Appositional growth adds layers to bone surface.

• Remodeling: Osteoclasts resorb bone; osteoblasts form new bone.

• Calcium Homeostasis: Regulated by parathyroid hormone (increases blood calcium) and calcitonin (decreases blood calcium).

Bone Fractures and Healing

Fractures are breaks in bone, classified by type and mechanism. Healing involves several stages.

• Types of Fractures: Closed, open, comminuted, spiral, compression, impacted, greenstick (incomplete).

• Fracture Healing: Hematoma formation, fibrocartilage callus, bony callus, remodeling.

Axial Skeleton

The axial skeleton includes the skull, vertebral column, and thoracic cage, providing central support and protection.

• Skull: Cranium (protects brain) and facial bones (form face).

• Vertebral Column: 33 vertebrae (cervical, thoracic, lumbar, sacral, coccygeal), intervertebral discs, vertebral structure (body, arch, processes).

• Thoracic Cage: Sternum and 12 pairs of ribs (true, false, floating).

Appendicular Skeleton

The appendicular skeleton consists of the limbs and girdles, enabling movement and manipulation of the environment.

• Shoulder Girdle: Clavicle and scapula connect upper limb to trunk.

• Upper Limb: Humerus, radius, ulna, carpals, metacarpals, phalanges.

• Pelvic Girdle: Hip bones (ilium, ischium, pubis), acetabulum, true/false pelvis.

• Lower Limb: Femur, tibia, fibula, patella, tarsals, metatarsals, phalanges.

Joints

Definition and Classification

Joints (articulations) are sites where two or more bones meet, classified by movement and structure.

• Functionally: Synarthroses (no movement), amphiarthroses (some movement), diarthroses (free movement).

• Structurally: Fibrous (no movement), cartilaginous (some movement), synovial (free movement).

Types of Joints

• Fibrous Joints: Bones joined by fibrous tissue (e.g., sutures of skull, syndesmoses).

• Cartilaginous Joints: Bones joined by cartilage (e.g., symphysis, synchondrosis).

• Synovial Joints: Freely movable, characterized by articular cartilage, synovial cavity, synovial fluid, reinforcing ligaments.

Types of Synovial Joints

• Plane Joint: Flat surfaces, gliding movements.

• Hinge Joint: Cylindrical end fits into trough-shaped surface (e.g., elbow, knee).

• Pivot Joint: Rounded end rotates within a ring (e.g., atlas-axis).

• Condyloid Joint: Rounded projection fits into concavity (e.g., metacarpophalangeal joints).

• Saddle Joint: Both surfaces concave and convex (e.g., thumb).

• Ball-and-Socket Joint: Spherical head fits into round socket (e.g., shoulder, hip).

Motions of Synovial Joints

• Gliding: Sliding movements.

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

• Rotation: Bone turns around its axis.

• Special Movements: Dorsiflexion, plantar flexion, supination, pronation, inversion, eversion, protraction, retraction, elevation, depression, opposition.

Major Joints and Their Features

• Shoulder Joint: Ball-and-socket, multi-axial, reinforced by rotator cuff muscles.

• Elbow Joint: Hinge, uniaxial, trochlea of humerus and notch of ulna.

• Hip Joint: Ball-and-socket, multi-axial, head of femur and acetabulum.

• Knee Joint: Largest, hinge, reinforced by ligaments (ACL, PCL, MCL, LCL).

• Ankle Joint: Hinge, tibia and fibula with talus.

Muscular System

Overview of Muscle Tissues

Muscle tissue is specialized for contraction and movement. There are three types: skeletal, cardiac, and smooth.

• Skeletal Muscle: Striated, voluntary, attached to bones, multinucleate cells called fibers.

• Cardiac Muscle: Striated, involuntary, found only in the heart, cells connected by intercalated discs and gap junctions.

• Smooth Muscle: Non-striated, involuntary, found in walls of hollow organs, spindle-shaped cells.

Skeletal Muscle Connective Tissue Layers

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds groups of muscle fibers (fascicles).

• Epimysium: Surrounds entire muscle.

Microscopic Anatomy of Skeletal Muscle

• Muscle Fiber: Elongated cell, multinucleate.

• Sarcolemma: Cell membrane of muscle fiber.

• Sarcomere: Basic contractile unit, contains actin (thin) and myosin (thick) filaments.

• Alternating Light and Dark Bands: I bands (light), A bands (dark).

Muscle Functions

• Produce Movement: Muscles contract to move body parts.

• Maintain Posture: Muscles stabilize joints and maintain body position.

• Generate Heat: Muscle activity produces heat for temperature regulation.

Example Table: Classification of Joints

Key Formula: Calcium Homeostasis

Regulation of blood calcium:

Additional info: Some details, such as the specific names of bones and joint types, have been expanded for clarity and completeness. The table and formulas are provided for academic context and exam preparation.