Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

Chapter 9: Joints and Articulations The bones of the human skeleton are rigid and relatively inflexible. Movements can occur only at articulations, or joints, where two bones interconnect. The joint type and amount of movement is determined by its structure. Each joint represents a compromise between the need for strength and the need for mobility. 9.1 Classification of Joints Two classification methods are used to categorize joints: range of motion and anatomical organization. The first is a functional category based on the amount of movement possible, known as the range of motion (ROM). Each functional group is subdivided based on the anatomical structure of the joint. The type of joint that is immovable is called a synarthrosis . A slightly movable joint is an amphiarthrosis . A freely movable joint is a diarthrosis . The second classification scheme relies on the anatomical organization of the joint. In this framework, joints are classified as bony, fibrous, cartilaginous, or synovial. Synarthrose (Immovable Joints) At a synarthrosis, the bony edges are close together and many interlock. These strong joints are located where movement between bones is prohibited. There are four major types of synarthroses. A synarthrotic joint, called a suture, is located only between the bones of the skull. Teeth are bound to bony sockets in the maxillae and mandible by a gomphosis . A synchondrosis is a rigid, cartilaginous bridge between two articulating bones. When two bones fuse and the boundary between them disappears, an immovable joint, known as a synostosis , has formed. Amphiarthroses (Slightly Movable Joints) An amphiarthrosis permits more movement than a synarthrosis but is much stronger than a freely movable joint. Cartilage or collagen fibers connect the articulating bones. There are two major types of amphiarthrotic joints: syndesmosis and symphysis. At a syndesmosis , a ligament connects the bones. An example is the articulation between the tibia and fibula. A symphysis , or symphyseal joint, has articulating bones separated by a wedge or pad of fibrous cartilage. Some examples of symphyses are the articulation between the bodies of vertebrae (at the intervertebral disc). Diarthroses (Freely Movable Joints) Diarthroses, or synovial joints , permit the widest range of motion of the types of joints. They are typically located at the ends of long bones, such as those of the upper and lower limbs. A fibrous articular capsule surrounds the synovial joint, and a synovial membrane lines the walls of the articular cavity. There are several components of synovial joints: the articular cartilages, synovial fluid, and various accessory structures.

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