Articulations/joints

Articulations/joints

1. Functional classification of joints

   • movement-based classification
   • Synarthroses
     • immovable joints
     • Amphiarthroses
       • slightly movable
       • Diarthroses
         • freely movable joints

2. Structural classification of joints

   • Fibrous joints
     • - synarthroses - held together  by fibrous connective tissue - ex. suture- short fibers that allow very little movement; found between bones of the skull
     • Cartilaginous joints
       • - synarthroses and amphiarthrosis - held together by cartilage - lack a joint cavity - 2 types: 1. synchondrosis and 2. symphysis
       • Synovial joints
         • - diarthrosis - has a fluid-filled joint cavity separating the articulating bones - allow a large range of motion
         • Structure of synovial joints
           • 1. articular cartilage- hyaline cartilage covering the ends of the articulating bones 2. joint (synovial) cavity- space between end of bones lined by synovial membrane and containing synovial fluid 3. articular capsule- encloses joint. It has two layers: outer fibrous capsule and inner synovial membrane 4. synovial fluid- secreted by synovial membrane and lubricates joint to prevent friction 5. reinforcing ligaments- provide extra strength and stabilization
           • Special features of synovial joints
             • menisci
               • - (c-shaped) fibrocartilage pad to stabilize the joint and minimize the wear on the articulating surfaces - found in the knee, jaw
               • bursae
                 • (cushions) - pouchlike sacs of synovial membrane filled with synovial fluid located between muscle or tendons and bone - *bursitis= water on the knee= inflammation of a bursa  - housemaid's knee is caused by excessive pressure
                 • tendon sheath
                   • - similar to bursa, but long and cylindrical- found where a tendon crosses a bone - allows the tendon to glide through the sheath
             • Stability of synovial joints
               • Determined by: 1. articular surfaces: a large surface area and a good fit between the articulating portion of bones improve stability ex. hip is more stable than leg due to deep articulation 2. ligaments: more ligaments=more stability 3. *muscle tone: tendons are kept taut by the tone of their muscles  - this is the most important stabilizing factor
               • Movement of synovial joints
                 • - origin vs insertion - muscle contracts across a joint and the insertion moves toward the origin
                 • gliding movements
                   • - flat surfaces slide over each other  ex. carpals
                   • angular movements
                     • 1. flexion, a movement in the sagittal plane, will decrease the joint angle - brings articulating bones closer together 2. extension increases the joint angle
                     • flexion
                       • - this action decreases the joint angle articulating bones closer together in the sagittal plane
                     • extension
                       • - this action increases the joint angle
                     • hyperextension
                       • - forms a joint angle greater than 180 degrees
                     • dorsiflexion
                       • - this action flexes the ANKLE back up
                     • plantar flexion
                       • - opposite of dorsiflexion; pointing the TOES down
                     • abduction
                       • - this action moves the limbs or digits away from midline
                     • adduction
                       • - this action moves the limbs or digits toward midline
                     • circumduction
                       • - circular, cone-like movement of limbs while proximal end remains fixed
                     • rotational movements
                       • rotation
                         • ex. shaking the head "no", medial or lateral rotation of arm or thigh
                       • supination
                         • - rotating forearm so that the palm is up
                       • pronation
                         • - rotating the forearm so the palm is down
                       • inversion
                         • - moving the sole of the foot inward
                       • eversion
                         • - moving the sole of the foot outward
                       • opposition
                         • - moving the thumb to touch the other fingers
                 • Types of synovial joints
                   • plane joints
                     • - bones with flat surfaces that allow for gliding movement - nonaxial - ex. intercarpal and intertarsal joints and intervertebral articular processes
                     • hinge joints
                       • - cylindrical projection of one bone fits into concave surface  of another bone, allowing bending in one plane - nonaxial - ex. elbow, joints between phalanges
                       • pivot joints
                         • - rounded end of one bone fits into a sleeve or depression on another, allowing rotation around an axis - ex. joint between atlas and dens of axis, proximal joint between radius and ulna
                         • condylar joints
                           • - oval convex end of one bone fits into an oval depression on another, allowing biaxial movement - ex. joint between radius and carpals, and metacarpals and phalanges.
                           • saddle joints
                             • - two bones with saddle-shaped ends, allowing biaxial movement - ex. joint between trapezium and first metacarpal
                             • ball-and-socket joints
                               • - rounded ball on one bone fits into concave depression on another, allowing multiaxial movement - ex. shoulder joint and hip joint
       • Symphysis
         • - amphiarthroses - covered by hyaline cartilage and having a fibrocartilage pad between them - ex. intervertebral joints  and pubic symphysis
       • Synchondrosis
         • - synarthroses - held together by hyaline cartilage - ex. epiphyseal plate and costal cartilage (between first rib and sternum)