Comprehensive Study Guide: Skeletal and Muscular Systems in Anatomy & Physiology

Skeletal System

Overview of Bone Structure and Function

The skeletal system provides the framework for the body, protects vital organs, and facilitates movement. Bones are dynamic organs with multiple functions and structural features.

• Functions of Bones: Support, protection, movement, mineral storage, blood cell formation (hematopoiesis), and energy storage.

• Types of Bone Tissue: Compact bone (dense, strong) and spongy bone (porous, lightweight).

• Classification of Bones: Long, short, flat, irregular, and sesamoid bones.

• Examples: Femur (long bone), sternum (flat bone), vertebrae (irregular bone).

Bone Anatomy and Development

Bones have complex anatomy and undergo continuous growth and remodeling throughout life.

• Gross Anatomy: Typical long bone features include diaphysis (shaft), epiphyses (ends), metaphysis, medullary cavity, periosteum, and endosteum.

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

• Bone Formation: Two main processes: intramembranous ossification (flat bones) and endochondral ossification (long bones).

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

• Remodeling: Continuous process involving osteoblasts (bone-forming cells), osteoclasts (bone-resorbing cells), and osteocytes (mature bone cells).

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

Axial and Appendicular Skeleton

The human skeleton is divided into axial and appendicular components, each with distinct bones and functions.

• Axial Skeleton: Skull, vertebral column, thoracic cage (ribs and sternum).

• Appendicular Skeleton: Pectoral girdle, upper limbs, pelvic girdle, lower limbs.

• Key Bones: Clavicle, scapula, humerus, radius, ulna, femur, tibia, fibula.

• Functions: Axial skeleton protects vital organs; appendicular skeleton enables movement.

Joints (Articulations)

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

• Classification: Fibrous (immovable), cartilaginous (slightly movable), synovial (freely movable).

• Fibrous Joints: Sutures (skull), syndesmoses (between tibia and fibula), gomphoses (teeth).

• Synovial Joints: Characterized by joint cavity, articular cartilage, synovial fluid, and supporting ligaments.

• Types of Synovial Joints: Plane, hinge, pivot, condyloid, saddle, ball-and-socket.

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

Table: Comparison of Joint Types

Joint Type	Structure	Movement	Example
Fibrous	Dense connective tissue	Immovable	Sutures of skull
Cartilaginous	Cartilage	Slightly movable	Intervertebral discs
Synovial	Joint cavity, synovial fluid	Freely movable	Shoulder, knee

Muscular System

Overview of Muscle Types and Functions

The muscular system enables movement, maintains posture, and produces heat. Muscles are classified by structure and function.

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

• Functions: Movement, stability, heat production, control of body openings.

• Muscle Attachments: Origin (fixed point), insertion (movable point).

Skeletal Muscle Structure and Contraction

Skeletal muscles are composed of muscle fibers organized into fascicles, which are bundled together to form the muscle.

• Microscopic Anatomy: Muscle fiber, myofibrils, sarcomeres, myofilaments (actin and myosin).

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

• Sliding Filament Theory: Muscle contraction occurs when myosin heads bind to actin filaments and pull them inward.

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

Equation:

$\text{Force} = \text{Cross-sectional area} \times \text{Tension per unit area}$

Muscle Actions and Naming

Muscles are named based on location, shape, size, direction of fibers, number of origins, and action.

• Prime Movers (Agonists): Main muscle responsible for movement.

• Antagonists: Oppose the action of the prime mover.

• Synergists: Assist the prime mover.

• Fixators: Stabilize the origin of the prime mover.

• Example: Biceps brachii (agonist for elbow flexion), triceps brachii (antagonist).

Major Muscles of the Human Body

The human body contains over 600 muscles, each with specific origins, insertions, and actions.

• Head and Neck: Masseter, temporalis, sternocleidomastoid.

• Torso: Pectoralis major, rectus abdominis, latissimus dorsi.

• Upper Limb: Deltoid, biceps brachii, triceps brachii.

• Lower Limb: Gluteus maximus, quadriceps femoris, hamstrings, gastrocnemius.

Table: Major Muscle Groups and Actions

Muscle Group	Location	Primary Action
Quadriceps	Anterior thigh	Knee extension
Hamstrings	Posterior thigh	Knee flexion
Deltoid	Shoulder	Arm abduction
Gastrocnemius	Calf	Plantar flexion

Cardiac and Smooth Muscle

Cardiac muscle is found only in the heart and is responsible for pumping blood. Smooth muscle is found in the walls of hollow organs and regulates internal movements.

• Cardiac Muscle: Striated, involuntary, intercalated discs, rhythmic contractions.

• Smooth Muscle: Non-striated, involuntary, slow contractions, found in digestive tract, blood vessels.

• Comparison: Skeletal muscle is voluntary and striated; cardiac is involuntary and striated; smooth is involuntary and non-striated.

Additional info:

• Some content was expanded for clarity and completeness, including definitions, examples, and tables.

• Equations and tables were inferred from standard Anatomy & Physiology curriculum.