Skeletal Tissues, Joints, and Muscle Tissue: Study Guide

Chapter 6: Skeletal Tissues

Overview of Skeletal Tissues

The skeletal system is composed of specialized connective tissues that provide support, protection, and movement. The two main types of tissues are bone and cartilage, each with distinct structures and functions.

• Bone Tissue: A rigid connective tissue that forms the majority of the skeleton, providing structural support and protection for organs.

• Cartilage Tissue: A flexible connective tissue found in joints, respiratory structures, and other areas requiring support with flexibility.

• Functions of the Skeletal System: Support, protection, movement, mineral storage, blood cell production (hematopoiesis), and energy storage.

Cartilage Types and Structure

• Hyaline Cartilage: Most abundant; found in nose, trachea, larynx, and at the ends of long bones.

• Elastic Cartilage: Contains elastic fibers; found in the ear and epiglottis.

• Fibrocartilage: Contains thick collagen fibers; found in intervertebral discs and pubic symphysis.

• Structure: Chondrocytes (cartilage cells) are located in lacunae within a matrix of collagen and elastic fibers.

Bone Classification and Structure

• Shape-based Classification: Long, short, flat, and irregular bones.

• Composition-based Classification: Compact (dense) bone and spongy (cancellous) bone.

• Gross Anatomy: Diaphysis (shaft), epiphyses (ends), metaphysis, articular cartilage, periosteum, endosteum, and medullary cavity.

• Microscopic Anatomy: Osteons (Haversian systems) in compact bone; trabeculae in spongy bone.

Bone Markings and Ossification

• Bone Markings: Projections, depressions, and openings that serve as attachment sites for muscles, ligaments, and tendons or as passageways for blood vessels and nerves.

• Ossification: The process of bone formation, including intramembranous (flat bones) and endochondral (long bones) ossification.

• Growth: Bones grow in length at the epiphyseal plate and in thickness by appositional growth.

Bone Remodeling and Homeostasis

• Bone Remodeling: Ongoing replacement of old bone tissue by new bone tissue, involving osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells).

• Calcium Homeostasis: Regulated by parathyroid hormone (PTH), calcitonin, and vitamin D.

• Hormonal Regulation: PTH increases blood calcium by stimulating osteoclasts; calcitonin lowers blood calcium by inhibiting osteoclasts.

Fractures and Bone Repair

• Types of Fractures: Open (compound), closed (simple), comminuted, greenstick, spiral, impacted, depressed.

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

• Osteoporosis: A condition characterized by decreased bone mass and increased fracture risk, common in older adults.

Chapter 8: Joints

Classification and Structure of Joints

Joints, or articulations, are connections between bones that allow for movement and provide mechanical support.

• Structural Classification: Fibrous, cartilaginous, and synovial joints.

• Functional Classification: Synarthroses (immovable), amphiarthroses (slightly movable), diarthroses (freely movable).

• Synovial Joints: Characterized by a joint cavity filled with synovial fluid; includes structures such as articular cartilage, joint capsule, synovial membrane, and ligaments.

Types of Synovial Joints and Movements

• Types: Plane, hinge, pivot, condyloid, saddle, and ball-and-socket joints.

• Movements: Gliding, flexion, extension, abduction, adduction, rotation, circumduction, inversion, eversion, dorsiflexion, plantar flexion, supination, pronation.

Joint Stability and Function

• Stability Factors: Shape of articular surfaces, ligament number and location, muscle tone.

• Joint Disorders: Arthritis (inflammation of joints), dislocations, sprains, and bursitis.

Chapter 10: Muscle Tissue

Types and Characteristics of Muscle Tissue

Muscle tissue is specialized for contraction and is classified into three types: skeletal, cardiac, and smooth muscle.

• Skeletal Muscle: Voluntary, striated, attached to bones, responsible for body movement.

• Cardiac Muscle: Involuntary, striated, found only in the heart, responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs (e.g., intestines, blood vessels).

Muscle Structure and Function

• Muscle Fiber: A single muscle cell, containing myofibrils composed of actin and myosin filaments.

• Sarcomere: The functional unit of muscle contraction, defined by Z lines.

• Connective Tissue Coverings: Endomysium (around each fiber), perimysium (around fascicles), epimysium (around entire muscle).

Muscle Contraction and Physiology

• Sliding Filament Model: Muscle contraction occurs as actin and myosin filaments slide past each other, shortening the sarcomere.

• Excitation-Contraction Coupling: Involves the transmission of an action potential along the sarcolemma, release of calcium ions, and interaction of actin and myosin.

• ATP Role: Provides energy for muscle contraction and relaxation.

• Motor Unit: A motor neuron and all the muscle fibers it innervates.

Muscle Metabolism and Fatigue

• Energy Sources: ATP, creatine phosphate, anaerobic glycolysis, and aerobic respiration.

• Muscle Fatigue: The inability to contract despite continued stimulation, often due to ATP depletion or ion imbalances.

• Oxygen Debt: The extra oxygen required after exercise to restore metabolic conditions.

Muscle Fiber Types and Adaptation

• Slow-Twitch (Type I): Fatigue-resistant, adapted for endurance.

• Fast-Twitch (Type II): Fatigue quickly, adapted for rapid, powerful movements.

• Adaptation: Exercise can increase muscle size (hypertrophy) and endurance.

Smooth Muscle

• Location: Found in walls of hollow organs.

• Contraction: Involuntary, regulated by autonomic nervous system, hormones, and local factors.

• Calcium Binding: Calcium binds to calmodulin to initiate contraction (unlike troponin in skeletal muscle).

Table: Types of Bone Fractures

Type of Fracture	Description
Open (Compound)	Bone breaks through the skin
Closed (Simple)	Bone does not break through the skin
Comminuted	Bone is broken into several pieces
Greenstick	Bone bends and cracks, common in children
Spiral	Fracture spirals around the bone, often due to twisting injury
Impacted	Broken bone ends are forced into each other
Depressed	Broken bone portion is pressed inward, typical of skull fracture

Key Equations

• Calcium Homeostasis:

$\text{PTH} \uparrow \rightarrow \text{Osteoclast activity} \uparrow \rightarrow \text{Blood Ca}^{2+} \uparrow$

$\text{Calcitonin} \uparrow \rightarrow \text{Osteoclast activity} \downarrow \rightarrow \text{Blood Ca}^{2+} \downarrow$

• Sliding Filament Model:

$\text{Muscle Contraction:} \quad \text{Actin} + \text{Myosin} + \text{ATP} \rightarrow \text{Cross-bridge cycling and sarcomere shortening}$

Additional info:

• Some explanations and context have been expanded for clarity and completeness.

• Table entries and equations are based on standard Anatomy & Physiology content.