Skeletal and Muscular Systems: Study Guide for Anatomy & Physiology

Chapter 6: Skeletal System

Functions and Structure of the Skeletal System

The skeletal system provides the framework for the body, supports and protects organs, enables movement, stores minerals, and houses bone marrow for blood cell production.

• Functions: Support, protection, movement, mineral storage (especially calcium and phosphorus), and blood cell formation (hematopoiesis).

• Bone Types: Long, short, flat, and irregular bones, each with distinct shapes and functions.

Bone Structure and Growth

Bones are complex organs composed of several tissue types. Their structure and growth patterns are essential for understanding bone health and development.

• Long Bone Anatomy: Diaphysis (shaft), epiphysis (ends), epiphyseal plate (growth plate), medullary cavity, periosteum, endosteum.

• Children vs. Adults: Epiphyseal plates are present in children (site of bone growth); in adults, these plates ossify and become epiphyseal lines.

Microscopic Structure of Bone

Bones contain both compact and spongy tissue, each with specialized cells and matrix components.

• Compact Bone: Dense outer layer; contains osteons (Haversian systems).

• Spongy Bone: Lighter, found at bone ends; contains trabeculae.

• Bone Cells: Osteoblasts (build bone), osteocytes (maintain bone), osteoclasts (break down bone).

Bone Development and Growth

Bone formation (ossification) occurs through two main processes: intramembranous and endochondral ossification.

• Ossification: Process by which bone forms from pre-existing connective tissue.

• Growth in Length: Occurs at epiphyseal plates via chondrocyte proliferation and ossification.

• Growth in Width: Appositional growth via osteoblast activity in the periosteum.

Bone Remodeling and Hormonal Regulation

Bone is a dynamic tissue, constantly being remodeled in response to mechanical stress and hormonal signals.

• Remodeling: Balance between osteoblast and osteoclast activity.

• Hormones: Parathyroid hormone (PTH) increases blood calcium by stimulating osteoclasts; calcitonin lowers blood calcium by inhibiting osteoclasts.

Fractures and Bone Repair

Bones can break (fracture) due to trauma or disease. The body repairs fractures through a series of stages.

• Types of Fractures: Simple, compound, comminuted, greenstick, etc.

• Stages of Fracture Repair:

  1. Hematoma formation

  2. Fibrocartilaginous callus formation

  3. Bony callus formation

  4. Bone remodeling

Table: Major Stages of Fracture Repair

Stage	Description
Hematoma Formation	Blood clot forms at fracture site
Fibrocartilaginous Callus	Soft callus of collagen and cartilage forms
Bony Callus	New bone replaces soft callus
Bone Remodeling	Bone is reshaped to original form

Bone Disorders and Prevention

Various disorders can affect bone health, including osteoporosis and abnormal curvatures.

• Osteoporosis: Decreased bone mass and increased fracture risk; prevention includes adequate calcium/vitamin D and weight-bearing exercise.

• Abnormal Curvatures: Scoliosis (lateral curve), kyphosis (hunchback), lordosis (swayback).

Axial and Appendicular Skeleton

The human skeleton is divided into axial (skull, vertebral column, thoracic cage) and appendicular (limbs, girdles) components.

• Axial Skeleton: Skull, vertebral column, thoracic cage.

• Appendicular Skeleton: Limbs, pectoral (shoulder) girdle, pelvic girdle.

Joints and Articulations

Joints (articulations) connect bones and allow movement. They are classified by structure and function.

• Structural Classifications: Fibrous, cartilaginous, synovial.

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

• Synovial Joints: Most movable; types include plane, hinge, pivot, condylar, saddle, and ball-and-socket.

Arthritis and Joint Disorders

Arthritis is a common joint disorder characterized by inflammation and pain.

• Types: Osteoarthritis (degenerative), rheumatoid arthritis (autoimmune), gouty arthritis (uric acid crystals).

• Symptoms: Pain, swelling, reduced mobility.

Chapter 6: Muscular System

Functions and Types of Muscle Tissue

Muscle tissue is specialized for contraction and movement. There are three main types, each with unique characteristics.

• Functions: Movement, posture, joint stabilization, heat production.

• Types: Skeletal (voluntary, striated), cardiac (involuntary, striated), smooth (involuntary, non-striated).

Properties of Muscle Tissue

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten forcibly.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to return to original length.

Muscle Structure and Organization

Muscles are composed of bundles of fibers, each containing myofibrils made of actin and myosin filaments.

• Connective Tissue Sheaths: Endomysium (around fibers), perimysium (around fascicles), epimysium (around whole muscle).

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

Neuromuscular Junction and Muscle Contraction

Muscle contraction is initiated by nerve impulses at the neuromuscular junction.

• Events: Calcium influx, acetylcholine (ACh) release, depolarization, action potential propagation.

• Sliding Filament Theory: Actin and myosin filaments slide past each other to shorten the muscle.

• ATP: Required for contraction and relaxation; produced via aerobic and anaerobic pathways.

Types of Muscle Contractions

• Isometric: Muscle tension without length change.

• Isotonic: Muscle changes length (concentric or eccentric) while tension remains constant.

Muscle Fatigue and Recovery

Muscle fatigue occurs when ATP production cannot keep up with demand, leading to decreased performance.

Body Movements and Muscle Groups

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

• Muscle Roles: Prime movers (agonists), antagonists, synergists, fixators.

• Fascicle Arrangement: Parallel, pennate, convergent, circular (affects muscle function and strength).

Major Muscles and Disorders

• Major Muscle Groups: Rotator cuff, hamstrings, quadriceps, etc.

• Muscle Disorders: Myasthenia gravis (autoimmune), muscular dystrophy (genetic).

• Atrophy: Decrease in muscle size due to disuse.

• Hypertrophy: Increase in muscle size due to exercise.

Additional info: Some details, such as specific table numbers and figure references, were inferred from standard Anatomy & Physiology textbooks to provide a complete and coherent study guide.