Chapter 8: Basic Functions and Classification of Joints PDF

8.1 **Basic Functions of Joints** Joints, known as articulations, play a crucial role in the skeletal system. Their primary functions include: 1. **Enable Movement**: - Joints allow bones to move relative to each other, facilitating motions such as walking, running, bending, and l...

8.1 **Basic Functions of Joints** Joints, known as articulations, play a crucial role in the skeletal system. Their primary functions include: 1. **Enable Movement**: - Joints allow bones to move relative to each other, facilitating motions such as walking, running, bending, and lifting. This movement is made possible by the contraction of surrounding muscles that exert force across the joints. 2. **Provide Stability**: - Some joints are designed for maximum stability, allowing little to no movement. This is important in protecting vital structures, such as the brain within the skull or supporting the spine. 3. **Allow for Growth**: - Joints like the epiphyseal plates (growth plates) in long bones are critical during growth and development. These temporary joints are where long bones lengthen during childhood and adolescence. **Classification of Joints** Joints can be classified in two distinct ways: **functionally** based on the amount of movement they allow, and **structurally** based on their anatomical features. **Functional Classification** The functional classification of joints revolves around the degree of mobility they provide: 1. **Synarthrosis**: - **Definition**: These joints allow no movement between articulating bones. - **Stability**: They provide maximum stability. - **Examples**: Sutures in the skull, the gomphosis joint (where teeth meet the jawbone). 2. **Amphiarthrosis**: - **Definition**: These joints allow a small amount of movement between bones. - **Stability**: They offer significant stability while permitting limited movement. - **Examples**: Intervertebral discs (between vertebrae) and the pubic symphysis. 3. **Diarthrosis**: - **Definition**: These are freely movable joints. - **Stability**: They provide the least amount of stability but allow for a wide range of specific movements. - **Examples**: Most joints in the limbs, including the knee, elbow, and shoulder joints. **Structural Classification** The structural classification of joints is based on the type of connective tissue that links the bones and the presence or absence of a joint space: 1. **Fibrous Joints**: - **Definition**: These joints are united by collagen fibers of dense regular connective tissue. - **Joint Space**: No joint space is present. - **Functional Classification**: Typically synarthroses or amphiarthroses. - **Examples**: Sutures of the skull, syndesmoses (such as between the radius and ulna), and gomphoses (such as teeth in their sockets). 2. **Cartilaginous Joints**: - **Definition**: These joints have cartilage between the articulating bones (hyaline cartilage or fibrocartilage). - **Joint Space**: No joint space is present. - **Functional Classification**: Often classified as synarthroses or amphiarthroses. - **Examples**: The epiphyseal plates in growing bones (hyaline cartilage) and the pubic symphysis (fibrocartilage). 3. **Synovial Joints**: - **Definition**: These joints have a joint cavity filled with synovial fluid that allows for a wide range of motion. - **Joint Space**: A fluid-filled joint space is present. - **Functional Classification**: Classified as diarthroses. - **Examples**: Knee, elbow, hip, and shoulder joints. 8.2 **Comparison of the Three Subclasses of Fibrous Joints** Fibrous joints are characterized by the presence of dense regular collagenous connective tissue that connects articulating bones. They are generally immobile (synarthroses), but the specific type of fibrous joint can influence the degree of mobility and functional characteristics. The three subclasses of fibrous joints are **sutures**, **gomphoses**, and **syndesmoses**. **1. Sutures** - **Definition**: Sutures are joints between the bones of the skull. - **Structure**: The edges of skull bones have interlocking, zigzag, or serrated margins, connected by very short collagen fibers. - **Function**: Sutures are designed for maximum stability and protection, making them synarthroses (immovable joints). - **Example**: Coronal suture between the frontal and parietal bones of the skull. - **Fusion**: Over time, sutures can fuse together (synostosis) as a person ages. **2. Gomphoses** - **Definition**: Gomphoses are joints that connect teeth to their sockets in the maxilla or mandible (tooth sockets). - **Structure**: Each tooth is anchored in its socket by the periodontal ligament, a dense fibrous connective tissue. - **Function**: Gomphoses are also synarthroses and provide stability to the teeth during chewing and speaking. - **Example**: The joint formed between a tooth and its alveolus (the bony socket in the jaw) is the only gomphosis in the human body. **3. Syndesmoses** - **Definition**: Syndesmoses are joints where the articulating bones are connected by a ligament, specifically an interosseous membrane or ligament. - **Structure**: These joints consist of a longer distance between the bones than in sutures or gomphoses, with fibers of collagen providing some elasticity. - **Function**: Syndesmoses allow for limited movement (amphiarthroses), enabling some degree of rotation or pivoting. - **Examples**: - Between the radius and ulna in the forearm. - Between the tibia and fibula in the leg. **Comparison of the Two Subclasses of Cartilaginous Joints** Cartilaginous joints connect bones via cartilage and lack a joint cavity. There are two main types: **synchondroses** and **symphyses**. **1. Synchondroses** - **Definition**: Synchondroses are joints where the bones are connected exclusively by hyaline cartilage. - **Structure**: The cartilage is typically tough yet flexible, allowing minimal to no movement. - **Function**: Functionally, synchondroses are synarthroses; they provide stability and rigidity. - **Examples**: - **Epiphyseal Plates**: Found in growing long bones where they contribute to bone lengthening. - **Costochondral Joints**: Between the ribs and costal cartilages, where the first rib connects to the manubrium of the sternum. **2. Symphyses** - **Definition**: Symphyses are joints where the bones are united by a fibrocartilage pad. - **Structure**: The fibrocartilage allows for slight movement and helps absorb shock and distribute pressure. - **Function**: As amphiarthroses, symphyses provide some mobility while offering structural integrity and support. - **Examples**: - **Intervertebral Joints**: Between vertebral bodies, where intervertebral discs act as shock absorbers. - **Pubic Symphysis**: Located between the pubic bones, allowing slight movement, especially during childbirth when more flexibility is needed 8.3 **Identify the Structural Components of a Synovial Joint** 1. **Joint Cavity (Synovial Cavity)**: - A distinct space between the ends of the articulating bones, allowing for a range of movement. 2. **Articular Capsule**: - **Outer Fibrous Layer**: Composed of dense irregular connective tissue that helps stabilize the joint and prevent dislocation. It isolates the internal environment of the joint from the surrounding blood supply. - **Inner Synovial Membrane**: Lined with loose connective tissue, this membrane secretes synovial fluid and provides nutrients and waste removal for the joint cells. It covers all areas of the joint cavity not adorned by cartilage. 3. **Synovial Fluid**: - **Lubrication**: Reduces friction and protects the articulating surfaces. - **Nutrient Supply**: Provides nutrients, such as glucose, to the cells within the joint and removes metabolic wastes. - **Shock Absorption**: Distributes stress across the joint, reducing the impact on bone surfaces during movement. 4. **Articular Cartilage**: - A thin layer of hyaline cartilage covering the articulating surfaces of the bones, which provides a smooth and low-friction surface for joint movement. It is avascular, relying on synovial fluid for nutrition and waste removal. 5. **Other Components**: - **Adipose Tissue**: Provides cushioning and helps with shock absorption around the joint. - **Nerves**: Supply sensory information such as pain and proprioception (joint position awareness). - **Blood Vessels**: Supply nutrients and oxygen to the articular capsule and help with waste removal. 6. **Stabilizing Structures**: - **Ligaments**: Connective tissue that connects bone to bone, contributing to joint stability. They can be intrinsic (part of the capsule) or extrinsic (external to the capsule). - **Tendons**: Connect muscle to bone and may cross the joint to help stabilize it. - **Bursae**: Fluid-filled sacs that reduce friction between moving parts around a joint. - **Tendon Sheaths**: Specialized bursae that encase tendons at certain joints, providing additional protection. **LO 8.3.2: Compare and Contrast Synovial Joints with Fibrous and Cartilaginous Joints** **1. Movement:** - **Synovial Joints**: Freely movable (diarthroses), allowing a wide range of motion. - **Fibrous Joints**: Generally immovable (synarthroses), such as sutural joints in the skull. - **Cartilaginous Joints**: Permit limited movement (amphiarthroses), for instance, between vertebrae. **2. Structural Characteristics:** - **Synovial Joints**: Characterized by the presence of a joint cavity filled with synovial fluid, an articular capsule, and articulating surfaces covered with articular cartilage. - **Fibrous Joints**: Lack a joint cavity; bones are connected by dense connective tissue (e.g., sutures and syndesmoses). - **Cartilaginous Joints**: Also lack a joint cavity; bones are connected by cartilage (e.g., hyaline cartilage in synchondroses or fibrocartilage in symphyses). **3. Blood Supply and Nutrition:** - **Synovial Joints**: The articular cartilage is avascular, relying solely on synovial fluid for nutrient delivery and waste removal. - **Fibrous and Cartilaginous Joints**: Typically have a better blood supply, which allows for more direct nutrient delivery. **4. Stability:** - **Synovial Joints**: Most mobile yet least stable; require external support for stability (from ligaments, muscles, and tendons). - **Fibrous Joints**: Highly stable due to their fixed structures and density of connective tissue. - **Cartilaginous Joints**: Provide moderate stability; some movement allowed while still being relatively fixed, thanks to the nature of cartilage. **5. Examples:** - **Synovial Joints**: Knee, elbow, shoulder, and hip joints. - **Fibrous Joints**: Sutures of the skull, syndesmosis between radius and ulna. - **Cartilaginous Joints**: Pubic symphysis and intervertebral discs. 8.4 **8.4.2: Describe and Demonstrate the Movements of Synovial Joints** This section provides an overview of the movements possible at synovial joints and classifies these movements based on their axes and functional categories. **Functional Classes of Synovial Joints** Synovial joints can be grouped based on the number of axes around which the bones can move: 1. **Nonaxial**: Allow motion in one or more planes but do not rotate around an axis. Example: Intercarpal joints in the wrist. 2. **Uniaxial**: Allow movement around a single axis. Example: Elbow joint (hinge joint) allows flexion and extension. 3. **Biaxial**: Permit movement around two axes. Example: Metacarpophalangeal joints (knuckles) allow flexion/extension and abduction/adduction. 4. **Multiaxial (Triaxial)**: Allow movement around three axes. Example: Shoulder joint allows flexion/extension, abduction/adduction, and rotation. **Types of Movements** Movements at synovial joints are classified into four general types: **gliding, angular, rotational, and special movements**. **Gliding Movements** - Gliding involves the sliding motion between articulating surfaces. - This movement occurs in a nonaxial manner, with bones sliding past each other without rotation. - Examples: Intertarsal joints (in the ankle) and intercarpal joints (in the wrist). **Angular Movements** Angular movements change the angle between two bones. Key types include: 1. **Flexion and Extension**: - **Flexion** decreases the angle between articulating bones (e.g., bending the elbow). - **Extension** increases the angle (e.g., straightening the elbow). - **Hyperextension** occurs when the angle increases beyond the normal range (e.g., moving the arm behind the body). 2. **Abduction and Adduction**: - **Abduction** moves a body part away from the midline (e.g., lifting arms sideways during a jumping jack). - **Adduction** brings a body part closer to the midline (e.g., returning arms to the side after a jumping jack). 3. **Lateral Flexion**: Side bending of the trunk or neck, decreasing the angle between the body and the side. 4. **Circumduction**: A circular movement involving flexion, extension, abduction, and adduction, resulting in a cone-shaped motion (e.g., moving the arm in a circular pattern at the shoulder). **Rotational Movements** - Rotation is a pivoting motion of a bone around its longitudinal axis. - **Internal (Medial) Rotation**: Rotating toward the midline of the body (e.g., twisting the thigh inward). - **External (Lateral) Rotation**: Rotating away from the midline of the body (e.g., twisting the thigh outward). - Example: Shaking the head to indicate \"no\" involves rotation at the atlantoaxial joint in the neck. **Special Movements** These movements are unique and typically involve specific joints: 1. **Opposition and Reposition**: - **Opposition** occurs at the thumb, allowing it to touch the other fingers. - **Reposition** is the return of the thumb to its anatomical position. 2. **Depression and Elevation**: - **Depression** moves a body part inferiorly (e.g., opening the mouth). - **Elevation** moves a body part superiorly (e.g., closing the mouth). 3. **Protraction and Retraction**: - **Protraction** moves a body part anteriorly (e.g., moving the mandible forward). - **Retraction** moves a body part posteriorly (e.g., bringing the mandible back). 4. **Inversion and Eversion**: - **Inversion** turns the sole of the foot medially. - **Eversion** turns the sole of the foot laterally. 5. **Dorsiflexion and Plantarflexion**: - **Dorsiflexion** is the upward movement of the foot at the ankle (toes pulled toward the head). - **Plantarflexion** is the downward movement of the foot at the ankle (toes pointed down). 6. **Supination and Pronation**: - **Supination** of the forearm turns the palm upward. - **Pronation** turns the palm downward. **Range of Motion (ROM)** The **range of motion** at a joint refers to the extent of movement it can achieve. Different types of joints offer varying degrees of motion: - **Nonaxial joints** (like intercarpal joints) tend to have a smaller range of motion. - **Multiaxial joints** (like the shoulder) often possess a greater range of motion due to their structural design. 8.5 [pictures](https://quizlet.com/62486262/synovial-joint-pictures-flash-cards/) [this too. (use for matching)](https://quizlet.com/37651859/matching-synovial-joints-in-the-body-flash-cards/) **LO 8.5.1: Describe the Anatomical Features of Each Structural Type of Synovial Joint** The six structural types of synovial joints, along with their anatomical features, are as follows: 1. **Plane Joint (Gliding Joint)** - **Shape**: Flat or slightly curved articulating surfaces. - **Movement**: Allows for nonaxial gliding movements. - **Example**: Intercarpal joints (wrist) and intertarsal joints (ankle). 2. **Hinge Joint** - **Shape**: A convex surface of one bone fits into a concave surface of another. - **Movement**: Uniaxial motion, allowing for flexion and extension. - **Example**: Elbow joint, knee joint, and interphalangeal joints of fingers and toes. 3. **Pivot Joint** - **Shape**: A rounded surface of one bone fits into a groove of another bone, allowing for rotation. - **Movement**: Uniaxial motion, enabling rotational movement around a single axis. - **Example**: Atlantoaxial joint (between the first and second cervical vertebrae). 4. **Condylar Joint (Ellipsoid Joint)** - **Shape**: An oval, convex surface of one bone fits into a shallow concave surface of another bone. - **Movement**: Biaxial motion, allowing for flexion, extension, abduction, and adduction. - **Example**: Metacarpophalangeal joints (knuckles) and some joints in the wrist. 5. **Saddle Joint** - **Shape**: Each articulating bone has both convex and concave surfaces, resembling a saddle. - **Movement**: Biaxial motion, permitting greater motion than condylar joints. - **Example**: Carpometacarpal joint of the thumb. 6. **Ball-and-Socket Joint** - **Shape**: A spherical (ball-shaped) end of one bone fits into a cup-shaped socket of another. - **Movement**: Multiaxial motion, allowing for movement in all three axes (flexion/extension, abduction/adduction, and rotation). - **Example**: Shoulder joint and hip joint. **LO 8.5.2: Describe Where Each Structural Type Can Be Found** - **Plane Joint**: - Found in the intercarpal joints of the wrist and intertarsal joints of the ankle. - **Hinge Joint**: - Found in the elbow, knee, and interphalangeal joints of fingers and toes. - **Pivot Joint**: - Found in the atlantoaxial joint (between the atlas and axis) and the proximal radioulnar joint. - **Condylar Joint**: - Found in the metacarpophalangeal joints of the fingers and at the wrist between the radius and carpal bones. - **Saddle Joint**: - Found at the carpometacarpal joint of the thumb. - **Ball-and-Socket Joint**: - Found in the shoulder joint (glenohumeral joint) and hip joint (acetabulofemoral joint). **LO 8.5.3: Predict the Kinds of Movements That Each Structural Type of Synovial Joint Will Allow** 1. **Plane Joint (Gliding Joint)**: - **Movements Allowed**: Nonaxial gliding movements, allowing bones to slide past each other in various directions but not around an axis. - **Example Movements**: Sliding movements during wrist and ankle motions. 2. **Hinge Joint**: - **Movements Allowed**: Uniaxial movement---primarily flexion and extension. - **Example Movements**: Bending and straightening the elbow or knee. 3. **Pivot Joint**: - **Movements Allowed**: Uniaxial rotation around a longitudinal axis. - **Example Movements**: Rotating the head side to side (as in \"no\") at the atlantoaxial joint. 4. **Condylar Joint (Ellipsoid Joint)**: - **Movements Allowed**: Biaxial movement---flexion and extension, as well as abduction and adduction. - **Example Movements**: Bending and waving fingers at the metacarpophalangeal joints. 5. **Saddle Joint**: - **Movements Allowed**: Biaxial movement, allowing for flexion/extension and abduction/adduction, plus some rotation. - **Example Movements**: Opposing and repositioning the thumb for grasping. 6. **Ball-and-Socket Joint**: - **Movements Allowed**: Multiaxial movement, allowing flexion/extension, abduction/adduction, and rotation. - **Example Movements**: Swinging arms in circles (shoulder joint) or moving legs in various directions (hip joint). 1. **Plane Joints** - Simplest and least mobile synovial joint - Features flat bone surfaces - Nonaxial, allowing only side-to-side \"gliding\" movements - Examples: intercarpal joints of the wrist and intertarsal joints of the ankle 1 2. **Hinge Joints** - Convex surface of one bone fits into a concave depression of another - Uniaxial motion, restricted to movement in one plane - Examples: elbow, knee, and interphalangeal joints of fingers and toes 1 3. **Pivot Joints** - Uniaxial joint with a rounded bone surface fitting into another bone\'s groove - Stabilized by a ringlike ligament - Example: atlantoaxial joint between first and second cervical vertebrae, allowing side-to-side head movement 1 4. **Condylar Joints** - Biaxial joint with an oval, convex bone surface in a shallow concave surface - Allows flexion, extension, abduction, and adduction - Examples: metacarpophalangeal joints (\"knuckles\") and parts of the wrist joint 1 5. **Saddle Joints** - Articulating surfaces resemble a horseback riding saddle - Biaxial with greater motion than condylar joints - Example: carpometacarpal joint of the thumb, enabling complex thumb movements 1 6. **Ball-and-Socket Joints** - Multiaxial joint with a spherical bone surface in a cup-shaped socket - Allows movement in all three axes - Most mobile but least stable joint type - Examples: shoulder and hip joints 1 The text emphasizes that joint mobility and stability are inversely related, with more mobile joints being more susceptible to injury. 8.6 **Elbow and Knee: Structural Features** 1. **Joint Type**: - Both the **elbow** and **knee** are classified as hinge joints, permitting primarily flexion and extension. - The elbow consists of two main articulations: the **humeroulnar** joint (between the trochlea of the humerus and the trochlear notch of the ulna) and the **humeroradial** joint (between the capitulum of the humerus and the head of the radius). - The knee has two articulations as well: the **tibiofemoral** joint (between the femoral and tibial condyles) and the **patellofemoral** joint (between the patella and the femur). 2. **Stability**: - The **elbow** is generally more stable due to its snug fit of articulating surfaces and robust supporting ligaments, including the **radial collateral ligament**, **ulnar collateral ligament**, and **anular ligament**. - The **knee**, while allowing some rotation and gliding during flexion, is less stable because of its more complex construction and the various forces at play. It contains several stabilizing structures such as the **anterior cruciate ligament (ACL)** and **posterior cruciate ligament (PCL)**, alongside the **medial** and **lateral menisci** for shock absorption. 3. **Motion**: - Both joints allow flexion and extension, but the knee has a greater degree of motion involving slight rotation when flexed, which is not a function of the elbow. - The elbow primarily enables motion in one plane whereas the knee, while primarily a hinge joint, accommodates additional movement due to its structure. **Shoulder and Hip: Structural Features** 1. **Joint Type**: - The **shoulder** (glenohumeral joint) and **hip** (coxal joint) are both classified as ball-and-socket joints. - The shoulder joint features a **shallow glenoid cavity** that receives the **humeral head**, permitting a wide range of motion but at the cost of stability. - The hip joint has a deeper **acetabulum**, which provides a more stable fit for the head of the femur, but allows less motion compared to the shoulder. 2. **Stability**: - The **hip** is inherently more stable than the shoulder due to its structure suited for weight-bearing and locomotion, reinforced by ligaments such as the **iliofemoral**, **pubofemoral**, and **ischiofemoral ligaments**. - The **shoulder**, despite its comprehensive range of motion, is more prone to dislocation, aided by the rotator cuff, but lacks the deep bony support significant in the hip. 3. **Motion**: - The shoulder allows for a greater variety of movements, including rotation, elevation, and circumduction due to its loose fit. - The hip enables a range of movements necessary for locomotion, including flexion, extension, abduction, adduction, and some rotational movements, but with constraints that provide greater stability. **Feature** **Elbow** **Knee** **Shoulder** **Hip** ----------------- ----------------------------- ------------------------------------ ------------------------------- ------------------------------------ Joint Type Hinge Hinge Ball-and-socket Ball-and-socket Articulations Humeroulnar, Humeroradial Tibiofemoral, Patellofemoral Glenohumeral Acetabulofemoral Stability More stable; snug fit Less stable; complex structure Less stable; shallow More stable; deep socket Range of Motion Primarily flexion/extension Flexion/extension, slight rotation Greater range; all directions Wide range, but less than shoulder \+