Skeletal System, Joints, and Muscular Tissue: Study Guide

Chapter 6: The Skeletal System

Functions of the Skeletal System

• Support: Provides structural framework for the body and supports soft tissues.

• 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, facilitating movement.

• Mineral Storage: Stores minerals, especially calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Production: Houses red bone marrow, which produces blood cells (hematopoiesis).

• Triglyceride Storage: Yellow bone marrow stores fat as an energy reserve.

Structure of Bone

• Diaphysis: Shaft of a long bone.

• Epiphyses: Ends of a long bone.

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

• Articular Cartilage: Hyaline cartilage covering joint surfaces.

• Periosteum: Dense connective tissue membrane covering bone except at joints.

• Medullary Cavity: Central cavity containing yellow marrow.

• Endosteum: Thin membrane lining the medullary cavity.

Types of Bones

• Long Bones: Longer than wide (e.g., femur, humerus).

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

• Flat Bones: Thin and often curved (e.g., sternum, ribs, skull bones).

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

• Sesamoid Bones: Develop within tendons (e.g., patella).

Bone Tissue and Types of Cells

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Comparison of Compact and Spongy Bone Tissue

Feature	Compact Bone	Spongy Bone
Structure	Dense, organized in osteons	Trabeculae network
Location	Diaphysis of long bones, outer layer	Epiphyses, inside flat bones
Function	Strength, support	Lightens bone, houses marrow

Bone Formation (Ossification)

• Intramembranous Ossification: Bone develops from fibrous membrane (e.g., flat bones of skull).

• Endochondral Ossification: Bone forms by replacing hyaline cartilage (e.g., long bones).

Bone Growth

• Longitudinal Growth: Occurs at epiphyseal plates; increases length of bones.

• Appositional Growth: Increases bone thickness by adding new bone to the surface.

Bone Remodeling

• Continuous process of bone resorption and deposition.

• Helps maintain calcium homeostasis and bone strength.

Role of Vitamins, Minerals, and Hormones

• Vitamins: Vitamin D (calcitriol) for calcium absorption; Vitamin C for collagen synthesis.

• Minerals: Calcium and phosphorus are essential for bone strength.

• Growth Hormone (GH): Stimulates bone growth.

• Sex Hormones: Promote growth spurt and closure of epiphyseal plates.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

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

• Calcitriol: Active form of vitamin D; increases calcium absorption from the gut.

Fracture and Repair of Bone

1. Hematoma Formation: Blood clot forms at fracture site.

2. Fibrocartilaginous Callus Formation: Collagen fibers and cartilage bridge the gap.

3. Bony Callus Formation: Spongy bone replaces the callus.

4. Bone Remodeling: Compact bone replaces spongy bone; bone returns to original shape.

Exercise and Bone Tissue

• Weight-bearing exercise stimulates bone growth and increases bone density.

Aging and Bone Tissue

• Bone mass decreases with age, especially in postmenopausal women.

• Increased risk of fractures and osteoporosis.

Bone Disorders

• Osteoporosis: Decreased bone mass and increased fragility.

• Rickets: Vitamin D deficiency in children; soft, weak bones.

• Osteomalacia: Vitamin D deficiency in adults; bone softening.

Chapter 8: Joints (Articulations)

Structural and Functional Classifications of Joints

• Structural Classification: Based on material binding bones and presence of joint cavity.

• Functional Classification: Based on degree of movement (synarthrosis, amphiarthrosis, diarthrosis).

Fibrous Joints

• Sutures: Immovable joints between skull bones.

• Syndesmoses: Bones connected by ligaments (e.g., distal tibiofibular joint).

• Gomphoses: Peg-in-socket joints (e.g., teeth in alveolar sockets).

Cartilaginous Joints

• Synchondroses: Bones united by hyaline cartilage (e.g., epiphyseal plate, first rib and sternum).

• Symphyses: Bones united by fibrocartilage (e.g., pubic symphysis, intervertebral discs).

Synovial Joints and Their Features

• Freely movable joints with a joint cavity.

• Features: Articular cartilage, joint (synovial) cavity, articular capsule, synovial fluid, reinforcing ligaments, nerves, and blood vessels.

Synovial Fluid and Its Functions

• Lubricates joint surfaces.

• Nourishes articular cartilage.

• Removes metabolic wastes.

Movements at Synovial Joints

• Gliding: Sliding movements (e.g., intercarpal joints).

• Angular Movements: Flexion, extension, hyperextension, abduction, adduction, circumduction.

• Rotation: Turning bone around its own axis (e.g., atlas and axis, shoulder, hip).

• Special Movements: Elevation, depression, protraction, retraction, inversion, eversion, dorsiflexion, plantar flexion, opposition.

Six Types of Synovial Joints

Type	Movement	Example
Plane	Gliding	Intercarpal joints
Hinge	Flexion/Extension	Elbow, knee
Pivot	Rotation	Atlas-axis, proximal radioulnar joint
Flexion/Extension, Abduction/Adduction	Wrist
Saddle	Flexion/Extension, Abduction/Adduction	Thumb (carpometacarpal joint)
Ball-and-Socket	All movements	Shoulder, hip

Aging and Joints

• Decreased synovial fluid production, thinning of articular cartilage, and reduced flexibility.

Joint Disorders

• Osteoarthritis: Degenerative joint disease; breakdown of articular cartilage.

• Rheumatoid Arthritis: Autoimmune inflammation of synovial membrane.

Chapter 10: Muscular Tissue

Types of Muscle Tissue and Their Differences

Type	Location	Control	Appearance
Skeletal	Attached to bones	Voluntary	Striated, multinucleated
Cardiac	Heart	Involuntary	Striated, branched, intercalated discs
Smooth	Walls of hollow organs	Involuntary	Non-striated, spindle-shaped

Functions and Properties of Muscular Tissue

• Contractility: Ability to shorten and generate force.

• Excitability: Responds to stimuli by generating action potentials.

• Conductivity: Conducts electrical signals along the membrane.

• Distensibility: Can be stretched without damage.

• Elasticity: Returns to original length after stretching.

Properties of Cardiac and Smooth Muscle

• Cardiac Muscle: Involuntary, striated, contracts rhythmically, contains intercalated discs for synchronized contraction.

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs, contracts slowly and can sustain contractions.

Skeletal Muscle Structure

• Myoblasts: Embryonic cells that fuse to form muscle fibers.

• Epimysium: Surrounds entire muscle.

• Perimysium: Surrounds muscle fascicles (bundles of fibers).

• Endomysium: Surrounds individual muscle fibers.

• Tendon: Connects muscle to bone.

Muscle Fiber Components and Functions

• Sarcolemma: Muscle cell membrane.

• Sarcoplasm: Cytoplasm of muscle fiber; contains myoglobin and glycogen granules.

• T-tubules: Invaginations of sarcolemma; conduct action potentials into fiber.

• Sarcoplasmic Reticulum (SR): Stores and releases calcium ions.

• Myofibrils: Bundles of contractile proteins (actin and myosin).

• Triads: T-tubule flanked by two terminal cisternae of SR.

• Myoglobin: Oxygen-binding protein in muscle.

• Glycogen Granules: Store glucose for energy.

Sarcomere and Filaments

• Sarcomere: Functional unit of muscle contraction; defined by Z-discs.

• Thin Filaments: Composed of actin, tropomyosin, and troponin.

• Thick Filaments: Composed of myosin.

• Troponin and Tropomyosin: Regulate binding of myosin to actin.

• Dystrophin: Links sarcomere to sarcolemma; mutations cause muscular dystrophy.

Events in Muscle Contraction and Relaxation

1. Excitation: Action potential arrives at neuromuscular junction; acetylcholine released.

2. Excitation-Contraction Coupling: Action potential travels along sarcolemma and T-tubules; Ca2+ released from SR.

3. Contraction: Ca2+ binds troponin, moves tropomyosin, myosin binds actin (cross-bridge), power stroke occurs (ATP required).

4. Relaxation: Ca2+ pumped back into SR, tropomyosin blocks binding sites, muscle fiber relaxes.

Role of Calcium and ATP

• Calcium: Initiates contraction by binding to troponin.

• ATP: Required for cross-bridge cycling and Ca2+ reuptake into SR.

Resting Membrane Potential (RMP) and Action Potential (AP) in Muscle Fiber

• RMP: Difference in charge across sarcolemma; typically -90 mV in skeletal muscle.

• Depolarization: Na+ influx makes inside positive.

• Repolarization: K+ efflux restores negative charge.

Neuromuscular Junction (NMJ)

• Synaptic Cleft: Gap between neuron and muscle fiber.

• Motor End Plate: Region of sarcolemma with acetylcholine receptors.

• Acetylcholine (ACh): Neurotransmitter that initiates muscle action potential.

• Acetylcholinesterase: Enzyme that breaks down ACh, ending stimulation.

ATP Production in Muscles

• Creatine Phosphate: Rapidly donates phosphate to ADP to form ATP.

• Anaerobic Respiration (Glycolysis): Produces ATP without oxygen; lactic acid is a byproduct.

• Aerobic Cellular Respiration: Uses oxygen to produce large amounts of ATP in mitochondria.

Motor Unit, Twitch, and Muscle Tone

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

• Twitch: Single contraction in response to a single stimulus; has latent, contraction, and relaxation periods.

• Muscle Tone: Slight, continuous contraction of muscle for posture and readiness.

Types of Muscle Fibers

Type	Contraction Speed	Fatigue Resistance	Color
Slow Oxidative (Type I)	Slow	High	Red
Fast Glycolytic (Type IIb)	Fast	Low	White
Fast Oxidative Glycolytic (Type IIa)	Fast	Intermediate	Pink

Types of Muscle Contractions

• Isotonic: Muscle changes length; includes concentric (shortening) and eccentric (lengthening) contractions.

• Isometric: Muscle length does not change; tension increases.

Effects of Training and Disuse

• Endurance Training: Increases oxidative capacity and fatigue resistance.

• Resistance Training: Increases muscle size (hypertrophy) and strength.

• Muscular Atrophy: Decrease in muscle size due to disuse or disease.

Additional info: Where details were not explicit, standard academic context was added for completeness (e.g., specific examples of bones, joint types, and muscle fiber types).