Read the following statements
(i) The bones are soft while cartilages are hard
(ii) Skeleton system gives the body support and protect inner organs
(iii) Doctors use X-ray films to examine the injuries of bones
(iv) The bones of cranium are flat and held firmly like a zipper
(v) Upper jaw is movable
(vi) Five vertebrae of hip and four vertebrae of tail are fused
How many statements are correct
Answers
Answer:
The point at which two or more bones meet is called a joint, or articulation. Joints are responsible for movement, such as the movement of limbs, and stability, such as the stability found in the bones of the skull.
Classification of Joints on the Basis of Structure
here are two ways to classify joints: on the basis of their structure or on the basis of their function. The structural classification divides joints into bony, fibrous, cartilaginous, and synovial joints depending on the material composing the joint and the presence or absence of a cavity in the joint.
Fibrous Joints
The bones of fibrous joints are held together by fibrous connective tissue. There is no cavity, or space, present between the bones and so most fibrous joints do not move at all, or are only capable of minor movements. There are three types of fibrous joints: sutures, syndesmoses, and gomphoses. Sutures are found only in the skull and possess short fibers of connective tissue that hold the skull bones tightly in place (Figure 19.23).
Figure_38_03_01
Figure 19.23. Sutures are fibrous joints found only in the skull.
Syndesmoses are joints in which the bones are connected by a band of connective tissue, allowing for more movement than in a suture. An example of a syndesmosis is the joint of the tibia and fibula in the ankle. The amount of movement in these types of joints is determined by the length of the connective tissue fibers. Gomphoses occur between teeth and their sockets; the term refers to the way the tooth fits into the socket like a peg (Figure 19.24). The tooth is connected to the socket by a connective tissue referred to as the periodontal ligament.
Figure_38_03_02
Figure 19.24. Gomphoses are fibrous joints between the teeth and their sockets. (credit: modification of work by Gray’s Anatomy)
Cartilaginous Joints
Cartilaginous joints are joints in which the bones are connected by cartilage. There are two types of cartilaginous joints: synchondroses and symphyses. In a synchondrosis, the bones are joined by hyaline cartilage. Synchondroses are found in the epiphyseal plates of growing bones in children. In symphyses, hyaline cartilage covers the end of the bone but the connection between bones occurs through fibrocartilage. Symphyses are found at the joints between vertebrae. Either type of cartilaginous joint allows for very little movement.
Synovial Joints
Synovial joints are the only joints that have a space between the adjoining bones (Figure 19.25). This space is referred to as the synovial (or joint) cavity and is filled with synovial fluid. Synovial fluid lubricates the joint, reducing friction between the bones and allowing for greater movement. The ends of the bones are covered with articular cartilage, a hyaline cartilage, and the entire joint is surrounded by an articular capsule composed of connective tissue that allows movement of the joint while resisting dislocation. Articular capsules may also possess ligaments that hold the bones together. Synovial joints are capable of the greatest movement of the three structural joint types; however, the more mobile a joint, the weaker the joint. Knees, elbows, and shoulders are examples of synovial joints.
Figure 38.25. Synovial joints are the only joints that have a space or “synovial cavity” in the joint.
Figure 19.25.
Synovial joints are the only joints that have a space or “synovial cavity” in the joint.
Classification of Joints on the Basis of Function
The functional classification divides joints into three categories: synarthroses, amphiarthroses, and diarthroses. A synarthrosis is a joint that is immovable. This includes sutures, gomphoses, and synchondroses. Amphiarthroses are joints that allow slight movement, including syndesmoses and symphyses. Diarthrosesare joints that allow for free movement of the joint, as in synovial joints.
Movement at Synovial Joints
The wide range of movement allowed by synovial joints produces different types of movements. The movement of synovial joints can be classified as one of four different types: gliding, angular, rotational, or special movement.
Gliding Movement
Gliding movementsoccur as relatively flat bone surfaces move past each other. Gliding movements produce very little rotation or angular movement of the bones. The joints of the carpal and tarsal bones are examples of joints that produce gliding movements.
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