Types of Joints in Anatomy

Joint Types

• Syndesmoses are fibrous joints where the connecting fibers are longer than those of sutures, for example, the distal ends connecting tibia and fibula.
• Cartilaginous joints connect bone ends with cartilage.
  • Amphiarthrotic cartilaginous joints are slightly movable, like the pubic symphysis of the pelvis and intervertebral joints of the spinal column.
  • Synarthrotic cartilaginous joints are immovable, like hyaline-cartilage epiphyseal plates of growing long bones and cartilaginous joints between first ribs and sternum.
• Synovial joints are freely movable joints where the articulating bone ends are separated by a joint cavity containing synovial fluid.
  • They account for all joints in the limbs.
  • Characteristics of Synovial Joints:
    • Articular cartilage (hyaline cartilage) covers the ends of the bones.
    • Fibrous articular capsule encloses the joint.
    • Joint cavity contains synovial fluid.
    • Reinforcing ligaments strengthen the fibrous capsule.
  • Bursae are flattened fibrous sacs lined with synovial membrane and containing synovial fluid. They are common where ligaments, muscles, skin, tendons, or bones rub together.

Muscles

• Muscle function is primarily contraction/shortening.
• Muscles are responsible for essentially all body movement.
• Similarities between skeletal and smooth muscle cells:
  • Elongated shape, referred to as muscle fibers.
  • Contain two types of myofilaments.
  • "Myo-" means muscle.
• Skeletal muscle fibers are packaged into organs called skeletal muscles:
  • Attached to bones or skin (facial muscles).
  • Long, cylindrical, multinucleate cells with striations.
  • Voluntary contraction (only muscle under conscious control).
  • No rhythmic contraction, range from slow to fast.

Connective Tissues in Skeletal Muscles

• Connective tissue wrappings provide strength and support to skeletal muscles.
  • Endomysium encloses each muscle fiber.
  • Perimysium wraps sheathed fibers together to form fascicles.
  • Epimysium covers the entire muscle and blends into tendons or aponeuroses.

Energy for Muscle Contractions

• ATP is the only energy source that can be used directly to power muscle activity.
• Three pathways for ATP regeneration:
  • Direct Phosphorylation of ADP by creatine phosphate:
    • Creatine phosphate (CP) is a high-energy molecule found in muscle fibers.
    • When ATP is depleted, CP transfers a phosphate group to ADP.
  • Aerobic Respiration:
    • Occurs in mitochondria.
    • Breaks down glucose into carbon dioxide and water.
    • Slow process that requires continuous oxygen and nutrients, high ATP yield.
  • Anaerobic glycolysis and lactic acid formation:
    • Initial steps of glucose breakdown occur in the cytosol (glycolysis).
    • Produces small amounts of ATP.
    • If oxygen is insufficient, pyruvic acid is converted to lactic acid.
    • Lactic acid can cause muscle soreness.
    • Produces much less ATP than aerobic respiration, but is faster.

Muscle Fatigue

• Muscle fatigue occurs when a muscle is unable to contract even though it is still being stimulated.
• Causes of muscle fatigue:
  • Oxygen debt: The muscle is not receiving enough oxygen to meet its demands.
  • Lactic acid buildup: Increasing acidity and lack of ATP cause the muscle to stop contracting.

Types of Muscle Contractions

• Isotonic contractions: Muscle shortens and movement occurs (bending knee, smiling).
• Isometric contractions: Muscle tension increases, but no movement occurs (lifting a heavy object).

Muscle Tone

• Muscle tone is continuous partial contractions of a muscle.
• Even when relaxed, some fibers are contracting, keeping the muscle firm and healthy.

Muscle Rules

• Antagonistic muscles: Oppose or reverse the action of another muscle.
• Synergistic muscles: Assist the prime mover by adding extra force to a movement.
• Fixator muscles: Stabilize the origin of a prime mover to prevent movement.

Intercostal Muscles

• Three layers: external, internal, innermost intercostal muscles.
• Origin (O): Ribs 1-11.
• Insertion (I): Ribs 2-12.
• Action (A): Raise the ribs, expand the chest cavity during breathing.

Joints

• All bones in the body form at least one joint with another bone.
• Functions of joints:
  • Hold bones together.
  • Allow mobility to the skeleton.

Classification of Joints

• Functional classification: Based on the amount of movement allowed.
  • Synarthroses: Immovable joints.
  • Amphiarthroses: Slightly movable joints.
  • Diarthroses: Freely movable joints.
• Structural classification: Based on the type of tissue that connects the bones.
  • Fibrous joints: Bones are united by fibrous tissue (immovable).
  • Cartilaginous joints: Bones are united by cartilage (slightly movable).
  • Synovial joints: Bones are separated by a joint cavity containing synovial fluid (freely movable).

Fibrous Joints

• Sutures of the skull are examples of fibrous joints.
  • Bone edges interlock and are bound by connective tissue fibers.
  • No movement allowed.
• Microfracture is a surgical technique to stimulate cartilage growth.
• Autologous Chondrocyte Implantation (ACI) involves culturing cartilage cells and implanting them back into the damaged area.
• Osteochondral Autograft Transplantation (OAT) involves transplanting healthy cartilage and underlying bone from a non-weight-bearing area.

Ligament Repair

• Surgical Ligament Reconstruction: Damaged ligament is replaced with a graft.
• Ligament Repair (Direct Suturing): Partial tears are sutured back together.
• Bracing and Rehabilitation: Bracing and physical therapy is often used for minor injuries.

Rigor Mortis and the Sliding Filament Theory

• Rigor mortis: Stiffening of muscles after death.
• Mechanism of Rigor Mortis:
  • ATP depletion: ATP production ceases, and myosin heads cannot detach from actin filaments.
  • Myosin binding: Without ATP, myosin remains bound to actin, resulting in muscle stiffness.
  • Muscle relaxation: Muscle relaxation requires ATP to detach myosin heads.
  • Cellular breakdown: Eventually, muscle proteins break down, and rigor mortis resolves.
• The sliding filament theory explains how muscle contraction occurs through the interaction of actin and myosin filaments.

Explore the various types of joints in human anatomy, including syndesmoses, cartilaginous, and synovial joints. This quiz covers their characteristics, movements, and examples to deepen your understanding of how our bodies are structured. Test your knowledge on joint classifications and their functions.