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BIOL 1117
Christopher Richardson

L15-Joints 10/9/13 • Joints (Articulations) o joint (articulation): any point where two bones meet; degree of mobility of bones at the meeting point or joint can vary widely o Kinesiology: the study of musculoskeletal movement  a branch of biomechanics: focuses on a broad variety of movements and mechanical processes in the body, including the physics of blood circulation, respiration, and hearing • Joints and Their Classification o joint name: typically derived from the names of the bones involved  glenohumeral joint (where the humerus meets the glenoid cavity), radioulnar joint (where radius meets the ulna), atlanto-occipital joint (where atlas vertebrate meets the occipital condyle) o four major joint categories:  fibrous joints  cartilaginous joints  bony joints  synovial joints o Joints are classified by how the adjacent bones are connected to each other including the differences in degree of mobility or movement of the bones • Fibrous Joints (Synarthrosis) o fibrous joint: adjacent bones are connected by collagen fibers that emerge from one bone and penetrate into the other o three kinds of fibrous joints  sutures  gomphoses  syndesmoses • Fibrous Joint – Sutures o sutures – immovable or slightly movable fibrous joints that closely bind the bones of the skull to each other • Fibrous Joint – Gomphoses o gomphosis – attachment of a tooth to its socket • Fibrous Joint-Syndesmosis o syndesmosis – a fibrous joint with two bones bound by long collagenous fibers which give the bones more mobility than other fibrous joints. o degree of mobility varies o The joint between the distal ends of the tibia and fibula is less movable than the joint between the radius and ulna shafts which is more movable, which allows for supination to pronation of the forearm • Cartilaginous Joints (amphiarthrosis) o cartilaginous joint: two bones are connected by cartilage o two types of cartilaginous joints  Synchondroses is a joint with the bones bound by hyaline cartilage; for ex, the temporary joint between the epiphysis and diaphysis of long bone of a child  Symphyses is a joint with the bones connected by fibrocartilage; for ex, the joint between two vertebral bodies which are joined by cartilaginous discs • Bony Joint (Synostosis) o bony joint: an immovable joint formed when the gap between two bones ossify, and they become in effect, a single bone o fibrous or cartilaginous joints can ossify. o Humans are born with right and left frontal and mandibular bones which soon fuse after birth into one frontal bone and one mandible o In older humans, cranial sutures can ossify with age as the suture disappears with suture line left behind o The epiphyses and diaphysis of long bones are joined by cartilage joints which become bony joints when the epiphyseal plate ossifies • Synovial Joint (Diarthrosis) o synovial joint: joint in which two bones are separated by a space called a joint cavity o most are freely movable o most structurally complex type of joint o most likely to develop painful dysfunction o most important joints for physical and occupational therapists, athletic coaches, nurses, and fitness trainers • Synovial Joint: GeneralAnatomy o articular cartilage: layer of hyaline cartilage that covers the facing surfaces of two bones o joint (articular) cavity: a narrow space that separates articular surfaces o synovial fluid: slippery lubricant in joint cavity  nourishes articular cartilage and removes waste  viscous, slippery texture also makes the movement of synovial joints almost friction free o joint (articular) capsule: connective tissue that encloses the cavity  outer fibrous capsule: continuous with periosteum of connecting bones  inner synovial membrane: contains mainly fibroblast-like cells that secrete synovial fluid and it has macrophages that remove debris from the cavity o accessory structures associated with synovial joints  tendon: a strip or sheet of tough collagenous connective tissue that attaches muscle to bone; most important structure for stabilizing a joint.  Remember, outer layer of periosteum of bone provides strong attachment and good continuity between bone, tendon and muscle.  ligament: similar tissue that attaches one bone to another  bursa: a fibrous sac filled with synovial fluid, located between adjacent muscles, where tendon passes over bone, or between bone and skin • Bursa cushions muscles, helps tendons slide more easily over joints; also modify the direction of tendons pull on the muscle  tendon sheaths: elongated cylindrical bursae wrapped around a tendon • Joints and Lever Systems o lever – any elongated, rigid object that rotates around a fixed point called a fulcrum o long bones act as levers to enhance the speed or power of limb movements o rotation occurs when an effort applied overcomes resistance (load) with output force at some other point  resistance arm and effort arm are described relative to fulcrum • Lever Systems o In skeletal anatomy, the fulcrum is the joint; the effort applied is applied by a muscle and the resistance can be an object, the limb itself, or tension in an opposing muscle o The effort is the input force at the point of the effort which generates the output force through the lever to oppose the resistance force or to act on an object • MechanicalAdvantage o advantage conferred by a lever can be of two kinds:  to exert more force against a resisting object than the input force applied to the lever  to move the resisting object farther or faster than
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