Chapter 8 – Articulations

Module 8.1: Classification of Joints

Joints, also known as articulations, are points where two or more bones meet. They are classified based on their structure and function, which determines their movement capabilities and stability.

• Structural Classification: Joints are categorized by the material binding the bones and the presence or absence of a joint cavity.

• Functional Classification: Joints are classified by the amount of movement they allow: synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable).

• Main Structural Types:

  • Fibrous Joints: Bones joined by dense connective tissue; no joint cavity.

  • Cartilaginous Joints: Bones joined by cartilage; no joint cavity.

  • Synovial Joints: Bones separated by a fluid-filled joint cavity; most movable type.

• Example: The sutures of the skull are fibrous joints, while the knee is a synovial joint.

Module 8.2: Fibrous and Cartilaginous Joints

Fibrous Joints

Fibrous joints are united by dense connective tissue and are typically immovable or allow very limited movement.

• Common Features: No joint cavity; bones connected by collagen fibers.

• Categories of Fibrous Joints:

  • Sutures: Found between skull bones; immovable (synarthroses).

  • Syndesmoses: Bones connected by ligaments; allow slight movement (amphiarthroses). Example: distal tibiofibular joint.

  • Gomphoses: Peg-in-socket joints; found between teeth and their sockets in the jaw. Immovable.

• Structural and Functional Properties of Sutures: Interlocking edges increase strength; allow for growth during childhood.

• Location of Sutures: Skull.

• Structural and Functional Properties of Gomphoses: Tooth held in socket by periodontal ligament; provides stability.

• Location of Gomphoses: Teeth in maxilla and mandible.

• Singular Form of Gomphoses: Gomphosis.

• Name for Ligament in Gomphoses: Periodontal ligament.

Cartilaginous Joints

Cartilaginous joints unite bones with cartilage and allow more movement than fibrous joints but less than synovial joints.

• Types of Cartilaginous Joints:

  • Synchondroses: Bones united by hyaline cartilage; mostly immovable. Example: epiphyseal plate in children, joint between first rib and sternum.

  • Symphyses: Bones united by fibrocartilage; slightly movable. Example: pubic symphysis, intervertebral discs.

• Properties of Symphyses: Strength and flexibility due to fibrocartilage.

• Properties of Synchondroses: Temporary or permanent; hyaline cartilage provides rigidity.

Module 8.4: Function of Synovial Joints

Synovial Joint Movements

Synovial joints are the most movable type of joint, allowing a wide range of movements. Movements are classified by the axes and planes in which they occur.

• Four Functional Classes: Based on axes and number of movements:

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

  • Uniaxial: Movement in one plane (e.g., elbow).

  • Biaxial: Movement in two planes (e.g., wrist).

  • Multiaxial: Movement in multiple planes (e.g., shoulder, hip).

• Types of Movements:

  • Flexion: Decreases the angle between bones (e.g., bending elbow).

  • Extension: Increases the angle between bones (e.g., straightening knee).

  • Hyperextension: Extension beyond anatomical position.

  • Abduction: Movement away from midline (e.g., raising arm sideways).

  • Adduction: Movement toward midline.

  • Rotation: Bone turns around its own axis (e.g., atlantoaxial joint in neck).

  • Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

  • Elevation/Depression: Lifting or lowering a body part (e.g., mandible).

  • Protraction/Retraction: Moving a body part forward or backward (e.g., jaw).

  • Pronation/Supination: Rotational movement of forearm; palm down (pronation) or up (supination).

• Example: The shoulder joint allows multiaxial movement, including rotation and circumduction.

Chapter 9: The Muscular System

Module 9.1: Overview of Skeletal Muscles

Skeletal muscles are composed of specialized tissues that allow voluntary movement and are attached to bones via tendons.

• Tissues Composing Skeletal Muscles: Skeletal muscle tissue, connective tissue, blood vessels, and nerves.

• Term for Skeletal Muscle Cell: Muscle fiber (myocyte).

• Connective Tissue Surrounding Muscle Structures:

  • Endomysium: Surrounds individual muscle fibers.

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

  • Epimysium: Surrounds the entire muscle.

• Continuity of Connective Tissue: The connective tissue merges with tendons, which are continuous with the periosteum of bone and perforating fibers, providing strong attachment.

• Example: The biceps brachii muscle is surrounded by epimysium, which connects to the tendon attaching to the radius.

Muscle Actions and Terminology

Understanding muscle actions involves knowing the origin, insertion, and movement produced by muscle contraction.

• Origin: Fixed attachment point of the muscle.

• Insertion: Movable attachment point; moves toward the origin during contraction.

• Prime Mover (Agonist): Muscle that provides most of the force for a movement.

• Antagonist: Muscle that opposes the action of the prime mover.

• Synergist: Muscle that assists the prime mover.

• Example: During elbow flexion, the biceps brachii is the prime mover, and the triceps brachii is the antagonist.

Lever Systems in the Body

Muscles and bones interact as lever systems to produce movement. Levers consist of a rigid bar (bone), a fulcrum (joint), effort (muscle force), and load (weight or resistance).

• Mechanical Advantage: Lever works efficiently when the effort arm is longer than the load arm; less force is needed to move the load.

• Mechanical Disadvantage: Lever works less efficiently when the effort arm is shorter; more force is needed.

• Example: The elbow joint acts as a fulcrum in forearm flexion.

• Equation:

Muscle Shapes and Naming

Muscles are named based on their shape, location, size, and function. Understanding these conventions helps in identifying muscle actions and locations.

• Examples of Muscle Shapes: Fusiform (biceps), parallel (sartorius), convergent (pectoralis major), pennate (rectus femoris), circular (orbicularis oris).

• Muscle Naming Conventions: Terms like "brevis" (short), "longus" (long), "maximus" (largest), "minimus" (smallest) indicate size or length.

• Example: The gluteus maximus is the largest muscle of the gluteal group.

Muscle Knots

Muscle knots, or myofascial trigger points, are localized areas of muscle tightness and pain.

• Causes: Overuse, poor posture, stress, or injury.

• Treatments: Massage, stretching, physical therapy, and rest.

• Example: Knots in the trapezius muscle are common in individuals with desk jobs.

Table: Comparison of Joint Types

Additional info: Academic context and definitions have been expanded for clarity and completeness. Images referenced in the original notes have been described and their content incorporated into the explanations.