Unit 2 Study Guide: Skeletal and Muscular Systems (Anatomy & Physiology)

Chapter 6: The Skeletal System

Major Divisions of the Skeletal System

The skeletal system is divided into two main regions, each with distinct anatomical and functional roles.

• Axial Skeleton: Composed of the skull, vertebral column, and thoracic cage. It provides support and protection for the brain, spinal cord, and vital organs.

• Appendicular Skeleton: Includes the limbs and girdles (pectoral and pelvic). It facilitates movement and interaction with the environment.

Types of Bones: Shape and Composition

Bones are classified by their shapes and internal structure, which relate to their functions.

• Long Bones: Longer than they are wide (e.g., femur). Function in movement and support.

• Short Bones: Nearly equal in length and width (e.g., carpals). Provide stability and support.

• Flat Bones: Thin and broad (e.g., sternum, skull). Protect internal organs.

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

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

• Compact Bone: Dense, forms the outer layer; provides strength.

• Spongy Bone: Porous, found at ends of long bones; reduces weight and contains marrow.

Functions of the Skeletal System

The skeletal system performs several vital functions:

• Support: Framework for the body.

• Protection: Shields vital organs (e.g., brain, heart).

• Movement: Acts as levers for muscles.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Occurs in red bone marrow (hematopoiesis).

• Triglyceride Storage: Yellow marrow stores fat.

Bone Tissue: Cellular and Extracellular Components

Bone tissue consists of specialized cells and a mineralized matrix.

• Cells: Osteogenic cells (stem cells), osteoblasts (bone-forming), osteocytes (mature bone cells), osteoclasts (bone-resorbing).

• Extracellular Matrix: Collagen fibers (flexibility), hydroxyapatite (calcium phosphate crystals for hardness).

Internal Structure of Compact and Spongy Bone

Bone structure varies between compact and spongy bone.

• Compact Bone: Organized into osteons (Haversian systems) with central canals, lamellae, lacunae, and canaliculi.

• Spongy Bone: Composed of trabeculae, spaces filled with marrow.

Structural Components of a Long Bone

Long bones have distinct regions important for growth and function.

• Diaphysis: Shaft, provides leverage.

• Epiphyses: Ends, contain spongy bone and red marrow.

• Metaphysis: Region between diaphysis and epiphysis; contains the epiphyseal plate (growth region).

• Medullary Cavity: Central cavity with yellow marrow.

• Periosteum: Outer membrane, site for muscle attachment.

• Endosteum: Lines the medullary cavity.

Functions of Structural Components

• Epiphyseal Plate: Site of longitudinal bone growth during development.

• Periosteum: Contains osteogenic cells for bone growth and repair.

• Medullary Cavity: Stores fat and houses marrow.

Osteogenic Cells and Bone Formation

Osteogenic cells are stem cells that differentiate into osteoblasts, initiating bone formation and repair.

Bone Formation: Intramembranous vs. Endochondral

Bone develops via two main processes:

• Intramembranous Ossification: Bone forms directly from mesenchymal tissue (e.g., flat bones of skull).

• Endochondral Ossification: Bone replaces a cartilage model (e.g., long bones).

Osteoblasts vs. Osteoclasts

• Osteoblasts: Build new bone matrix.

• Osteoclasts: Break down bone matrix for remodeling and calcium release.

Hormonal Regulation of Bone Growth

Bone growth is regulated by hormones such as growth hormone, sex hormones, and thyroid hormones.

Roles of Calcitonin, Parathyroid Hormone, and Calcitriol

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Parathyroid Hormone (PTH): Raises blood calcium by stimulating osteoclasts.

• Calcitriol: Increases calcium absorption from the gut.

Types of Fractures

• Simple (Closed): Bone breaks but does not pierce skin.

• Compound (Open): Bone breaks and pierces skin.

• Comminuted: Bone shatters into multiple pieces.

• Greenstick: Incomplete break, common in children.

• Transverse, Oblique, Spiral: Based on fracture direction.

Bone Healing Process

1. Hematoma formation

2. Fibrocartilaginous callus formation

3. Bony callus formation

4. Bone remodeling

Chapter 10: The Muscular System

Major Functions of Muscle Tissue

Muscle tissue enables movement, maintains posture, and generates heat.

• Movement: Locomotion and manipulation.

• Posture: Stabilizes joints and maintains body position.

• Heat Production: Byproduct of muscle activity.

Organization of Muscle Tissue

Muscle tissue is organized from microscopic to macroscopic levels.

• Muscle Fiber (Cell): Basic unit.

• Fascicle: Bundle of muscle fibers.

• Whole Muscle: Group of fascicles.

• Muscle Group: Multiple muscles working together.

Connective Tissue Layers

• Endomysium: Surrounds individual muscle fibers.

• Perimysium: Surrounds fascicles.

• Epimysium: Surrounds entire muscle.

• Fascia: Surrounds muscle groups.

Skeletal Muscle Fiber Anatomy

• T Tubules: Invaginations of the sarcolemma; transmit action potentials.

• Sarcoplasmic Reticulum: Stores and releases calcium ions.

• Myofibrils: Contain contractile proteins.

Sarcomere: Contractile and Structural Proteins

• Actin: Thin filament.

• Myosin: Thick filament.

• Titin, Nebulin, Tropomyosin, Troponin: Structural and regulatory proteins.

Sliding Filament Theory

Muscle contraction occurs as myosin heads bind to actin, pulling filaments past each other.

Anatomy of the Neuromuscular Junction

• Motor Neuron: Releases neurotransmitter (acetylcholine).

• Synaptic Cleft: Space between neuron and muscle fiber.

• Motor End Plate: Region of muscle fiber membrane with receptors.

Events at the Neuromuscular Junction

1. Action potential arrives at axon terminal.

2. Acetylcholine released into synaptic cleft.

3. Acetylcholine binds to receptors, triggering muscle action potential.

Excitation-Contraction Coupling

The process linking muscle fiber excitation to contraction via calcium release.

Contraction Cycle of Skeletal Muscle

1. ATP binds to myosin head.

2. Myosin head attaches to actin.

3. Power stroke moves actin filament.

4. ATP detaches myosin from actin.

Muscle Fatigue

Fatigue results from depletion of ATP, accumulation of lactic acid, and ionic imbalances.

Recovery Period

• Replenishment of oxygen and ATP.

• Removal of lactic acid.

• Restoration of ion concentrations.

ATP Production in Muscle Fibers

• Creatine Phosphate: Rapid ATP regeneration.

• Anaerobic Glycolysis: Produces ATP without oxygen.

• Aerobic Respiration: Produces most ATP, requires oxygen.

Sources of Energy in Muscle Fibers

• Stored ATP

• Creatine phosphate

• Glycogen

• Fatty acids

Length-Tension Relationship

The force a muscle can generate depends on its length at the time of contraction.

• Optimal overlap of actin and myosin produces maximal tension.

Definitions: Tension and Contraction

• Tension: Force produced by muscle contraction.

• Contraction: Shortening or development of tension in muscle.

Myogram of a Twitch Contraction

• Latent Period: Time between stimulus and contraction.

• Contraction Period: Muscle shortens and tension rises.

• Relaxation Period: Tension decreases, muscle returns to resting state.

Tension vs. Stimulus Frequency: Summation and Tetanus

• Summation: Increased tension due to rapid stimuli.

• Tetanus: Sustained contraction from high-frequency stimulation.

Fast vs. Slow Muscle Fibers

Characteristic	Fast Fibers	Slow Fibers
Contraction Speed	Rapid	Slow
Fatigue Resistance	Low	High
Color	White	Red
Metabolism	Anaerobic	Aerobic

Motor Unit

A motor unit consists of a motor neuron and all the muscle fibers it innervates.

Recruitment

Recruitment is the activation of additional motor units to increase muscle force.

Isotonic vs. Isometric Contraction

• Isotonic: Muscle changes length; tension remains constant.

• Isometric: Muscle length remains constant; tension increases.

Concentric vs. Eccentric Contraction

• Concentric: Muscle shortens while generating force.

• Eccentric: Muscle lengthens while resisting force.

Comparison of Muscle Types

Feature	Skeletal Muscle	Cardiac Muscle	Smooth Muscle
Striations	Present	Present	Absent
Control	Voluntary	Involuntary	Involuntary
Location	Attached to bones	Heart	Walls of organs
Regeneration	Limited	None	High

Additional info: These notes expand on the study guide outline by providing definitions, explanations, and examples for each listed topic, suitable for exam preparation in Anatomy & Physiology.