Skeletal and Muscular System: Study Guide

Skeletal System

Functions 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.

• Support: Provides structural support for the entire body.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Serves as levers for muscles to act upon.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Houses red bone marrow for hematopoiesis.

Bone Shapes

Bones are classified by shape, which relates to their function.

• Long bones: Longer than they are wide (e.g., femur, humerus).

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

• Flat bones: Thin and broad (e.g., skull, ribs, sternum).

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

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

Parts of a Long Bone

Long bones have distinct anatomical regions:

• Diaphysis: The shaft, composed mainly of compact bone.

• Epiphyses: The ends, containing spongy bone and red marrow.

• Metaphysis: Region between diaphysis and epiphysis; contains the growth plate.

• Medullary cavity: Central cavity containing yellow marrow (fat storage).

• Periosteum: Outer fibrous covering.

• Endosteum: Lining of the medullary cavity.

Compact vs. Spongy Bone

Bones contain two main types of tissue:

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

• Spongy bone (cancellous): Porous, found at ends of long bones and inside flat bones; contains red marrow.

Bone Composition and Cells

• Osteon: Structural unit of compact bone.

• Lacunae: Small spaces housing osteocytes.

• Cartilage: Flexible connective tissue; differs from bone in structure and function.

• Cartilage-specific cells: Chondrocytes.

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

Bone Growth and Development

• Types of bone growth: Intramembranous (flat bones) and endochondral (long bones).

• Interstitial growth: Growth in length at the epiphyseal plate.

• Appositional growth: Growth in thickness.

• Growth plate (epiphyseal plate): Site of lengthwise bone growth; replaced by bone at maturity.

• Hormones: Growth hormone, thyroid hormone, sex hormones regulate bone growth.

Bone Remodeling and Repair

• Fracture: A break in bone; repaired by hematoma formation, callus formation, and bone remodeling.

• Osteoporosis: Disease causing decreased bone mass; increases fracture risk.

• Osteomalacia: Softening of bones due to vitamin D deficiency.

• Negative feedback loop: Regulates calcium via calcitonin and parathyroid hormone (PTH).

Bone Surface Markings

Surface features of bones serve as attachment points for muscles, ligaments, and tendons, and as passageways for nerves and blood vessels.

Classification of Bones and Joints

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs and girdles.

• Joints (articulations): Classified by structure (fibrous, cartilaginous, synovial) and function (synarthrosis, amphiarthrosis, diarthrosis).

• Diseases of joints: Arthritis, gout, etc.

Muscular System

Functions of the Muscular System

The muscular system enables movement, maintains posture, stabilizes joints, and generates heat.

• Movement: Skeletal muscles contract to move bones.

• Posture: Continuous muscle contractions maintain body position.

• Joint stabilization: Muscles reinforce and stabilize joints.

• Heat production: Muscle activity generates heat for temperature regulation.

Muscle Structure

• Basic structure: Muscle fibers (cells) bundled into fascicles, surrounded by connective tissue (endomysium, perimysium, epimysium).

• Arrangement: Parallel, pennate, convergent, circular.

• Connective tissue: Supports and transmits force; includes tendons (connect muscle to bone).

Muscle Cell Structure

• Myofibrils: Contain actin and myosin filaments.

• Sarcomere: Functional unit of contraction; Z-line to Z-line.

• Other features: Sarcolemma (cell membrane), sarcoplasmic reticulum (stores Ca2+), mitochondria (energy production).

Muscle Attachment and Contraction

• Tendon: Connects muscle to bone.

• Origin: Fixed attachment point.

• Insertion: Movable attachment point.

• Contraction: Sliding filament theory—actin and myosin filaments slide past each other.

• Neuromuscular junction: Site where nerve meets muscle; acetylcholine triggers contraction.

• Role of calcium: Ca2+ ions enable actin-myosin binding.

• Motor unit: One motor neuron and all the muscle fibers it innervates.

Muscle Energy and Metabolism

• Energy sources: ATP, creatine phosphate, glucose (glycolysis), fatty acids.

• Aerobic respiration: Uses oxygen, produces more ATP, slower.

• Anaerobic respiration: No oxygen, less ATP, produces lactic acid.

• By-products: CO2, water, lactic acid.

Muscle Tone, Hypertrophy, and Disorders

• Muscle tone: Continuous, partial contraction of muscles.

• Hypertrophy: Increase in muscle size due to exercise.

• Rigor mortis: Stiffening of muscles after death due to lack of ATP.

• Muscle disorders: Examples include muscular dystrophy, myasthenia gravis.

Summary Table: Types of Joints

Structural Type	Example	Movement
Fibrous	Sutures of skull	Immovable
Cartilaginous	Intervertebral discs	Slightly movable
Synovial	Knee, shoulder	Freely movable

Key Equations

• Calcium homeostasis:

$\text{PTH} \uparrow \Rightarrow \text{Blood Ca}^{2+} \uparrow$

$\text{Calcitonin} \uparrow \Rightarrow \text{Blood Ca}^{2+} \downarrow$

• ATP production (aerobic):

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$

• ATP production (anaerobic):

$\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_3\text{H}_6\text{O}_3 + 2\text{ATP}$

Additional info:

• For lab material, review all bones, joints, and muscle structures as covered in lab handouts and practicals.

• Be familiar with terminology in bold from lecture slides for exam preparation.