BIOL 2113: Skeletal and Muscular Systems Study Guide

The Skeletal System

Cartilage and Bone Tissue Types

Cartilage and bone are specialized connective tissues with distinct properties and functions in the body.

• Cartilage Tissue: Contains chondrocytes within lacunae, embedded in a matrix rich in collagen and elastic fibers. Types include hyaline, elastic, and fibrocartilage.

• Bone Tissue: Contains osteocytes within lacunae, with a matrix hardened by calcium phosphate salts and collagen fibers.

• Extracellular Matrix (ECM): The non-cellular component present within all tissues and organs, providing structural and biochemical support to surrounding cells.

• ECM Consistency:

  • Hard: Bone tissue (due to mineralization)

  • Semi-solid: Cartilage (due to proteoglycans)

  • Soft: Loose connective tissue

• Rigidity: Bone is rigid; cartilage is flexible/bendy.

Structural Classes of Bone

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

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

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

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

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

• Sesamoid Bones: Embedded in tendons (e.g., patella)

• Sutural Bones: Small bones within cranial sutures

Compact Bone vs. Spongy Bone

Bones consist of two main types of tissue: compact and spongy bone.

• Compact Bone: Dense, forms the outer layer; contains osteons (Haversian systems) with concentric lamellae.

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

• Substructures:

  • Osteons: Cylindrical structures in compact bone

  • Lamellae: Layers of bone matrix

  • Trabeculae: Network of bony spines in spongy bone

Bone Marrow and Hematopoiesis

Bone marrow is a vital tissue for blood cell production.

• Yellow Marrow: Fat storage, found in medullary cavity of long bones

• Red Marrow: Site of hematopoiesis (blood cell formation), found in spongy bone of flat bones and epiphyses of long bones

• Hematopoiesis: Occurs in red marrow

Bone and Cartilage Cell Types

Various cell types are responsible for bone and cartilage formation and maintenance.

• Osteoblasts: Build bone matrix

• Osteocytes: Mature bone cells, maintain bone tissue

• Osteoclasts: Break down bone matrix

• Chondroblasts: Build cartilage matrix

• Chondrocytes: Mature cartilage cells

• Cell Maturation: Osteoblasts become osteocytes; chondroblasts become chondrocytes

Bone Formation and Growth

Bones form and grow through distinct processes.

• Endochondral Ossification: Bone develops from cartilage templates (most bones)

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue (flat bones)

• Appositional Growth: Growth in width by adding layers to the surface

• Interstitial Growth: Growth in length within the tissue

Hormonal Regulation of Bone Growth

Bone growth is regulated by hormones at different life stages.

• Pre-childhood: Growth hormone, thyroid hormone

• Post-childhood: Sex hormones (estrogen, testosterone)

Structure of the Long Bone

Long bones have distinct regions and internal structures.

• Diaphysis: Shaft, contains medullary cavity

• Epiphysis: Ends of the bone, contains spongy bone

• Metaphysis: Region between diaphysis and epiphysis

• Epiphyseal Plate: Growth plate, site of lengthwise growth

• Epiphyseal Line: Remnant of plate after growth stops

• Location of Compact/Spongy Bone: Compact bone in diaphysis; spongy bone in epiphyses

Joints: Functional and Structural Classification

Joints connect bones and allow movement; classified by function and structure.

• Functional Classification:

  • Synarthroses: Immovable joints

  • Amphiarthroses: Slightly movable joints

  • Diarthroses: Freely movable joints

• Structural Classification:

  • Fibrous Joints: Bones joined by dense connective tissue

    • Sutures: Skull

    • Syndesmoses: Ligaments

    • Gomphoses: Teeth sockets

  • Cartilaginous Joints: Bones joined by cartilage

    • Synchondroses: Hyaline cartilage

    • Symphyses: Fibrocartilage

  • Synovial Joints: Bones separated by a fluid-filled cavity

    • Hinge: Elbow

    • Ball-and-Socket: Shoulder, hip

    • Condylar/Ellipsoid: Wrist

    • Pivot: Atlas/axis

    • Saddle: Thumb

    • Plane: Intercarpal joints

Major Movement Types

Joints allow various movements essential for body function.

• Flexion/Extension: Decreasing/increasing angle between bones

• Abduction/Adduction: Moving limb away/toward midline

• Pronation/Supination: Rotating forearm

• Other Movements: Circumduction, rotation, elevation, depression, etc.

Abnormal Curves of the Spine

Spinal curves can deviate from normal in certain conditions.

• Scoliosis: Lateral curvature

• Kyphosis: Excessive thoracic curvature

• Lordosis: Excessive lumbar curvature

Axial Skeleton: Function and Named Bones

The axial skeleton supports and protects vital organs.

• Skull: Protects brain; includes frontal, parietal, occipital, temporal, sphenoid, ethmoid, mandible, maxilla, zygomatic, etc.

• Movable Skull Bone: Mandible

• Strongest Facial Bone: Mandible

• Strongest Skull Bone: Occipital (structurally)

• Skull Sutures:

  • Lambdoid: Parietal and occipital

  • Sagittal: Parietal bones

  • Squamosal: Parietal and temporal

  • Coronal: Frontal and parietal

  • Occipitomastoid: Occipital and mastoid

  • Metopic: Frontal bones (in infants)

• Vertebral Column: Cervical, thoracic, lumbar, sacral, coccygeal regions

• Intervertebral Discs: Fibrocartilage pads for shock absorption

• Thoracic Cage: Ribs, sternum, thoracic vertebrae

Appendicular Skeleton: Function and Named Bones

The appendicular skeleton enables movement and manipulation of the environment.

• Girdles:

  • Shoulder Girdle: Clavicle, scapula

  • Hip Girdle: Ilium, ischium, pubis

• Shoulder vs. Hip Girdle: Shoulder allows more movement due to shallow socket; hip is more stable

• Bones of Limbs: Humerus, radius, ulna, femur, tibia, fibula, etc.

• Strongest Bone: Femur

The Muscular System

Types of Muscle Tissue

Muscle tissue is classified by structure, function, and location.

• Skeletal Muscle: Voluntary, striated, attached to bones

• Cardiac Muscle: Involuntary, striated, found in heart

• Smooth Muscle: Involuntary, non-striated, found in walls of organs

• Heat Production: Skeletal muscle contracts to shiver and produce heat

Muscle Function and Energy

Skeletal muscle is responsible for voluntary movement and requires energy storage.

• Glycogen Stores: Provide rapid energy for contraction

• Heavy Breathing: Replenishes oxygen and removes lactic acid after activity

Muscle Contraction Mechanism

Muscle cells contract (shorten) to produce movement; they do not push or grow outward.

• Sliding Filament Model: Actin and myosin filaments slide past each other, shortening the sarcomere

• Equation for Muscle Force: $F = m \cdot a$

Muscle Cell Structure

Muscle fibers contain specialized organelles for contraction.

• Myofibrils: Bundles of contractile proteins

• Sarcomere: Smallest functional unit of myofibril

• Striated Muscle: Myofibrils present in skeletal and cardiac muscle

Sarcomere Structure

The sarcomere contains distinct bands, discs, lines, and zones.

• A Band: Length of thick filaments

• I Band: Thin filaments only

• Z Line: Boundary of sarcomere

• M Line: Center of sarcomere

• H Zone: Thick filaments only, no overlap

Types of Muscle Fibers

Muscle fibers differ in contraction speed and metabolic properties.

• Slow-Twitch (Type I): Oxidative, fatigue-resistant, high mitochondria

• Fast-Twitch (Type II): Glycolytic, rapid contraction, fatigue quickly

• Oxidative Fibers: Rely on aerobic metabolism, need more mitochondria

• Glycolytic Fibers: Rely on anaerobic metabolism

Table: Comparison of Muscle Fiber Types

Type	Contraction Speed	Metabolism	Mitochondria	Fatigue Resistance
Slow-Twitch (Type I)	Slow	Oxidative (Aerobic)	High	High
Fast-Twitch (Type II)	Fast	Glycolytic (Anaerobic)	Low	Low

Additional info: For diagrams and further details, refer to textbook figures as indicated in the study guide (e.g., Chapter 8 Focus Figure 8.1, Chapter 9 Figures 9.1 and 9.2).