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Joints and Muscle Tissue: Study Guide for Anatomy & Physiology I (Chapters 8 & 9)

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Chapter 8: Joints

Articulations (Joints)

Articulations, or joints, are sites where two or more bones meet. They are essential for movement and provide the skeleton with flexibility and mobility, while also holding bones together.

  • Definition: An articulation is a junction between two bones.

  • Function: Allow movement, provide stability, and connect bones.

Classification of Joints by Structure

Joints are classified structurally based on the material binding the bones and whether a joint cavity is present.

  • Fibrous Joints: Bones joined by dense fibrous connective tissue; no joint cavity. Examples: Sutures (skull), syndesmoses (distal tibiofibular joint), gomphoses (teeth in sockets).

  • Cartilaginous Joints: Bones united by cartilage; no joint cavity. Examples: Synchondroses (epiphyseal plates), symphyses (pubic symphysis).

  • Synovial Joints: Bones separated by a fluid-filled joint cavity. Examples: Most limb joints (shoulder, knee, hip).

Classification of Joints by Function

Functional classification is based on the amount of movement allowed:

  • Synarthroses: Immovable joints (e.g., sutures).

  • Amphiarthroses: Slightly movable joints (e.g., intervertebral discs).

  • Diarthroses: Freely movable joints (e.g., most limb joints).

Cartilaginous Joints

  • General Structure: Bones are united by cartilage; lack a joint cavity.

  • Types:

    • Synchondroses: Hyaline cartilage unites bones (e.g., epiphyseal plate, first rib and manubrium).

    • Symphyses: Fibrocartilage unites bones (e.g., pubic symphysis, intervertebral discs).

Synovial Joints

These are the most common and movable type of joint in the body.

  • Six General Features:

    1. Articular cartilage (hyaline): covers bone ends.

    2. Joint (synovial) cavity: space containing synovial fluid.

    3. Articular capsule: two layers (fibrous and synovial membrane).

    4. Synovial fluid: lubricates and nourishes articular cartilage.

    5. Reinforcing ligaments: strengthen the joint.

    6. Nerves and blood vessels: supply the joint.

Bursae and Tendon Sheaths

  • Bursae: Flattened sacs filled with synovial fluid; reduce friction where ligaments, muscles, skin, tendons, or bones rub together.

  • Tendon Sheaths: Elongated bursae that wrap around tendons subjected to friction.

  • Comparison: Both reduce friction, but tendon sheaths are specifically associated with tendons.

Stabilization of Synovial Joints

  • Articular surfaces: Shape determines possible movements.

  • Ligaments: Prevent excessive or undesirable motion.

  • Muscle tone: Keeps tendons taut and is the most important stabilizing factor.

Body Movements at Synovial Joints

  • Gliding: One flat bone surface glides over another (e.g., intercarpal joints).

  • Angular Movements: Increase or decrease the angle between bones (flexion, extension, abduction, adduction, circumduction).

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

  • Special Movements: Supination, pronation, dorsiflexion, plantar flexion, inversion, eversion, protraction, retraction, elevation, depression, opposition.

Types of Synovial Joints (by Movement)

Type

Movement

Example

Plane

Gliding

Intercarpal joints

Hinge

Flexion/Extension

Elbow, knee

Pivot

Rotation

Proximal radioulnar joint

Flexion/Extension, Abduction/Adduction

Metacarpophalangeal joints

Saddle

Flexion/Extension, Abduction/Adduction

Thumb (carpometacarpal joint)

Ball-and-socket

All movements

Shoulder, hip

Major Synovial Joints: Shoulder, Elbow, Hip, TMJ, Knee

  • Shoulder (Glenohumeral): Head of humerus and glenoid cavity of scapula; most mobile, least stable; frequent dislocation.

  • Elbow: Humerus, radius, ulna; hinge joint; flexion/extension; stable due to strong ligaments.

  • Hip: Head of femur and acetabulum; ball-and-socket; stable, less mobile than shoulder.

  • Temporomandibular Joint (TMJ): Mandibular condyle and temporal bone; modified hinge; allows opening/closing and side-to-side movement.

  • Knee: Femur, tibia, patella; largest, most complex; hinge with some rotation; stabilized by ligaments and menisci.

Common Joint Injuries

  • Sprains: Ligaments stretched or torn.

  • Dislocations: Bones forced out of alignment.

  • Torn Cartilage: Common in knee; may require surgery.

  • 3 C's of Knee Injury: Collateral ligaments, Cruciate ligaments, Cartilages (menisci).

Types of Arthritis

  • Osteoarthritis: Degenerative; wear and tear.

  • Rheumatoid Arthritis: Autoimmune; inflammation of synovial membrane.

  • Gouty Arthritis: Uric acid crystal deposition.

Lyme Disease

  • Cause: Bacterial infection (Borrelia burgdorferi) from tick bites.

  • Consequences: Joint pain, arthritis, neurological symptoms if untreated.

  • Geography: Less common on the West Coast due to lower prevalence of the tick vector.

Chapter 9: Muscles & Muscle Tissue

Types of Muscle Tissue

There are three types of muscle tissue, each with distinct structure and function.

Type

Location

Control

Striations

Function

Skeletal

Attached to bones

Voluntary

Yes

Movement, posture

Cardiac

Heart

Involuntary

Yes

Pumps blood

Smooth

Walls of hollow organs

Involuntary

No

Moves substances

Muscle Terminology

  • myo-, mys-: Prefixes meaning "muscle" (e.g., myofibril, epimysium).

  • sarco-: Prefix meaning "flesh" (e.g., sarcolemma, sarcoplasm).

Characteristics of Muscle Tissue

  • Excitability: Ability to receive and respond to stimuli.

  • Contractility: Ability to shorten forcibly.

  • Extensibility: Ability to be stretched.

  • Elasticity: Ability to recoil to resting length.

Functions of Muscle Tissue

  • Movement of body parts and substances

  • Maintaining posture

  • Stabilizing joints

  • Generating heat

Gross Structure of Skeletal Muscle

  • Composed of: Muscle fibers (cells), connective tissue, blood vessels, nerves.

  • Connective Tissue Sheaths:

    • Epimysium: Surrounds entire muscle.

    • Perimysium: Surrounds fascicles (bundles of fibers).

    • Endomysium: Surrounds each muscle fiber.

Microscopic Structure of Muscle Fibers

  • Myofibrils: Rod-like elements containing contractile proteins (myofilaments).

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

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

Sliding Filament Model of Contraction

Muscle contraction occurs as thin filaments (actin) slide past thick filaments (myosin), shortening the sarcomere.

  • Key Steps: Myosin heads bind to actin, pivot, detach, and re-cock, pulling actin filaments inward.

Sarcomere Structure

  • Sarcomere: Functional unit of muscle fiber; extends from Z disc to Z disc.

  • Myofilaments: Thick (myosin) and thin (actin) filaments.

Steps of Muscle Contraction

  1. Action potential arrives at neuromuscular junction.

  2. Acetylcholine released, binds to receptors on sarcolemma.

  3. Depolarization triggers action potential in muscle fiber.

  4. Calcium released from SR.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Cross bridge cycle begins (myosin binds to actin).

Neuromuscular Junction (NMJ) and Action Potential

  • NMJ: Site where motor neuron communicates with muscle fiber.

  • Action Potential: Electrical signal that travels along sarcolemma, leading to contraction.

Excitation-Contraction Coupling

  • Sequence of events linking action potential to muscle contraction.

  • Involves release of calcium and activation of cross bridge cycling.

Cross Bridge Cycle (4 Steps)

  1. Cross bridge formation (myosin binds to actin).

  2. Power stroke (myosin head pivots, pulling actin).

  3. Cross bridge detachment (ATP binds to myosin, releasing actin).

  4. Cocking of myosin head (ATP hydrolysis repositions head).

Homeostatic Imbalances at the NMJ

  • Myasthenia Gravis: Autoimmune disorder; antibodies block acetylcholine receptors.

  • Botox: Blocks acetylcholine release, causing paralysis.

Rigor Mortis

  • Occurs after death due to lack of ATP; myosin heads cannot detach from actin, causing stiffness.

ATP Regeneration in Muscle

  • Direct phosphorylation: Creatine phosphate + ADP → ATP + creatine.

  • Anaerobic glycolysis: Glucose → ATP + lactic acid (no oxygen required).

  • Aerobic respiration: Glucose + O2 → ATP + CO2 + H2O (requires oxygen).

Muscle Soreness

  • Often due to microtears and lactic acid accumulation after intense exercise.

Additional info: For detailed molecular mechanisms, refer to Table 9.3 in your textbook for a comprehensive comparison of muscle types.

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