Review of Key Concepts
Joints and Their Classification (p. 294)
- Arthrology is the study of joints; kinesiology is the study of musculoskeletal movement.
- Joints can be classified as diarthroses, amphiarthroses, or synarthroses according to their freedom of movement, and as fibrous, cartilaginous, bony, or synovial according to the manner in which the adjacent bones are joined.
Fibrous, Cartilaginous, and Bony
Joints (p. 295)
- In fibrous joints, two bones are joined by collagen fibers. Fibrous joints include sutures (immovable joints of the skull), gomphoses (joints between teeth and their sockets), and syndesmoses (in which bones are joined by a ligament).
- Sutures are classified as serrate, lap, or plane sutures according to the structure of the edges where the bones meet.
- In cartilaginous joints, two bones are joined by cartilage. Cartilaginous joints include synchondroses (bones joined by hyaline cartilage) and symphyses (bones joined by fibrocartilage).
- In bony joints, two bones are fused by osseous tissue so they appear as a single bone.
Synovial Joints (p. 298)
- In a synovial joint, two bones are separated by a joint cavity containing lubricating synovial fluid. The articulating surfaces of the adjacent bones are covered by a hyaline articular cartilage, and are sometimes held apart by a cartilaginous pad called a meniscus.
- Synovial joints commonly exhibit tendons (which join muscle to bone), ligaments (which join one bone to another), and bursae (sacs of synovial fluid outside the joint cavity).
- Synovial joints are described as monaxial, biaxial, or multiaxial depending on the planes in which they can move.
- The six types of synovial joints are ball-and-socket, hinge, saddle, pivot, gliding, and condyloid joints.
- Flexion is a movement that decreases the angle between two bones, as in flexing the elbow; extension straightens a joint to about a 180° angle; and hyperextension moves one bone beyond 180° from the other.
- Abduction moves a bone away from the midsagittal plane of the body, as in spreading the legs, and adduction moves it back.
- Elevation raises a bone such as the mandible and depression lowers it.
- Protraction thrusts a bone such as the clavicle or mandible forward and retraction draws it back.
- Lateral excursion moves the mandible to the right or left and medial excursion returns it to the middle.
- Circumduction moves the distal end of a bone in a circle while the proximal end remains relatively stationary.
- Rotation turns a bone on its longitudinal axis.
- Supination rotates the forearm so the palm faces forward or upward, and pronation turns it so the palm faces toward the rear or downward.
- Opposition moves the thumb toward the fingers and reposition moves it back to anatomical position.
- Dorsiflexion raises the toes relative to the heel and plantar flexion lowers the toes or raises the heel.
- Inversion turns the sole of the foot medially and eversion turns it laterally.
- The range of motion of a joint depends on the structure and action of the muscles, the structure of the bones, and the strength and tautness of tendons, ligaments, and joint capsules.
- A long bone acts as a lever, with a stationary fulcrum, an effort arm, and a resistance arm.
- The mechanical advantage (MA) of a lever is equal to the ratio of the length of the effort arm to the length of the resistance arm. A lever with an MA > 1 puts out more force than is put into it, and one with an MA < 1 puts out less force, but produces movements of greater speed or distance than the input.
- Levers of the body are classified as first-, second-, or third-class depending on the relative positions of the fulcrum, effort, and resistance.
Anatomy of Selected Diarthroses (p. 310)
- The temporomandibular (jaw) joint of the skull is the point at which the condyle of the mandible articulates with the mandibular fossa of the temporal bone. It is stabilized by two ligaments and contains a meniscus to absorb some of the pressure of a bite.
- The humeroscapular joint is the point at which the head of the humerus articulates with the glenoid cavity of the scapula. It is supported by a cartilaginous glenoid labrum, five major ligaments, the biceps brachii tendon, and tendons of the four rotator cuff muscles, and it exhibits four bursae.
- The elbow joint is a meeting of three bones—humerus, radius, and ulna— enclosed in a single joint capsule.
- The coxal (hip) joint is the point at which the head of the femur inserts into the acetabulum of the os coxae. It is supported by a cartilage ring, the acetabular labrum, and several ligaments.
- The tibiofemoral (knee) joint is the largest diarthrosis. The joint cavity contains two cartilage menisci and two cruciate ligaments, and there are numerous other ligaments and bursae external to the joint cavity.
- The talocrural (ankle) joint is a meeting of three bones—tibia, fibula, and talus—supported by numerous tight ligaments and crossed by the calcaneal tendon of the calf muscles.
Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill
Physiology: The Unity of Companies, 2003 Form and Function, Third Edition
Chapter 9 Joints 323
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