Diagram Of Joints In The Human Body – 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 the limbs, and stability, such as the stability of the skull bones.

There are two ways to classify joints: by their structure or by function. Structural classification divides joints into bony, fibrous, cartilaginous and synovial, depending on the material of which the joint is composed and the presence or absence of a cavity in the joint.

Diagram Of Joints In The Human Body

Diagram Of Joints In The Human Body

The bones of fibrous joints are held together by fibrous connective tissue. There is no cavity or space between the bones, so most fibrous joints do not move at all or are capable of only minor movements. There are three types of fibrous joints: sutures, syndesmoses and gomphos. Sutures occur only in the skull and contain short fibers of connective tissue that hold the bones of the skull tightly in place (Fig. 19.23).

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Syndesmoses are joints in which the bones are connected by a strip of connective tissue that allows greater movement than would be possible with a suture. An example of syndesmosis is the union of the tibia and fibula at the ankle joint. The range of motion in these types of joints is determined by the length of the connective tissue fibers. Gomphos arise between the teeth and their sockets; this term refers to the way the tooth fits into the socket like a peg (Fig. 19.24). The tooth is connected to the socket by connective tissue called the periodontal ligament.

Figure 19.24. Gomphos are fibrous compounds between teeth and their sockets. (credit: modification of Grey’s Anatomy)

Cartilaginous joints are joints in which the bones are connected by cartilage. There are two types of cartilaginous joints: synchondroses and symphyses. With synchondrosis, the bones are connected by hyaline cartilage. Synchondroses are found in the epiphyseal plates of growing bones in children. At the symphyses, hyaline cartilage covers the end of the bone, but the connection between the bones is through fibrocartilage. Symphyses are located at the junction of the vertebrae. Any type of cartilaginous joint allows very little movement.

Synovial joints are the only joints that have space between adjacent bones (Fig. 19.25). This space is called the synovial (or articular) cavity and is filled with synovial fluid. Synovial fluid lubricates the joint, reducing friction between bones and allowing greater mobility. The ends of the bones are covered with articular cartilage, hyaline cartilage, and the entire joint is surrounded by an articular capsule consisting of connective tissue that allows the joint to move, resisting dislocation. Joint capsules may also have ligaments that hold the bones together. Synovial joints are capable of the most motion of the three structural types of joints; however, the more mobile the joint, the weaker it is. Knees, elbows and shoulders are examples of synovial joints.

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The functional classification divides joints into three categories: synarthrosis, amphiarthrosis and diarthrosis. Synarthrosis is a joint that is immobile. This includes sutures, gomphoses and synchondroses. Amphiarthroses are joints that allow minor movements, including the syndesmosis and symphyses. Diarthroses are joints that allow free movement of the joint, as in synovial joints.

The wide range of motion allowed by synovial joints allows for different types of movements. The movement of synovial joints can be divided into four types: sliding, angular, rotational or special movement.

Sliding movements occur when the relatively flat surfaces of bones move past each other. Sliding movements cause very little rotation or angular movement of the bones. The joints of the carpal and tarsal bones are examples of joints that allow gliding movements.

Diagram Of Joints In The Human Body

Angular movements occur when the angle between the bones of a joint changes. There are several different types of angular movements, including flexion, extension, hyperextension, abduction, adduction, and circumduction. Bending or bending occurs when the angle between bones decreases. Moving the forearm up at the elbow or moving the wrist to move the arm toward the forearm are examples of flexion. Extension is the opposite of flexion because the angle between the bones of the joint increases. Straightening a limb after flexion is an example of extension. Extension beyond the normal anatomical position is called hyperextension. This involves moving the neck back to look up or bending the wrist so that the hand moves away from the forearm.

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Abduction occurs when the bone moves away from the midline of the body. Examples of abduction include moving the arms or legs laterally to lift them straight out to the side. Adduction is the movement of bone toward the midline of the body. The inward movement of the limbs after abduction is an example of adduction. Circumduction is a circular movement of a limb, similar to the circular movement of an arm.

Rotational motion is the movement of a bone as it rotates around its longitudinal axis. Rotation can be directed toward the midline of the body, which is called medial rotation, or away from the midline of the body, which is called lateral rotation. Moving the head from side to side is an example of rotation.

Some movements that cannot be classified as sliding, angular or rotational are called special movements. In inversion, the soles of the feet move inward toward the midline of the body. Eversion is the opposite of inversion, the movement of the sole of the foot outward, away from the midline of the body. Protraction is the movement of a bone forward in a horizontal plane. Retraction occurs when a joint returns to its original position after protraction. Protraction and retraction can be seen in the movement of the mandible as the jaw moves outward and then back inward. Lifting is the upward movement of the bone, such as when you shrug your shoulders, lifting your shoulder blades. Depression is the opposite of elevation—the downward movement of a bone, such as after the shoulders are shrugged and the shoulder blades return to their normal position from an elevated position. Dorsiflexion is the flexion of the ankle that raises the toes toward the knee. Plantar flexion is the flexion of the ankle joint when raising the heel, such as when standing on the toes. Supination is the movement of the radius and ulna of the forearm so that the palm faces forward. Pronation is the opposite movement in which the palm faces backward. Opposition is the movement of the thumb toward the fingers of one hand to grasp and hold objects.

Synovial joints are classified into six different categories based on the shape and structure of the joint. The shape of the joint influences the type of movement allowed by the joint (Fig. 19.26). These joints can be characterized as planar, hinge, hinge, condylar, saddle or ball and socket joints.

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Different types of joints allow different types of movement. Planar, hinge, hinge, condylar, saddle, and ball and socket joints are all types of synovial joints.

Planar joints have bones with articulating surfaces that are flat or slightly curved. These joints allow sliding movements, so they are sometimes called sliding joints. The range of motion in these joints is limited and does not involve rotation. Flat joints are found in the carpal bones of the hand and the tarsal bones of the foot, as well as between the vertebrae (Fig. 19.27).

The joints of the carpal bones of the wrist are an example of planar joints. (credit: modification of work by Brian K. Goss)

Diagram Of Joints In The Human Body

In hinge joints, the slightly rounded end of one bone fits into the slightly hollow end of another bone. Thus, one bone moves while the other remains motionless, like a door hinge. The elbow is an example of a hinge joint. The knee is sometimes classified as a modified hinge joint (Fig. 19.28).

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The elbow joint, where the radius bone articulates with the humerus bone, is an example of a hinge joint. (credit: modification of work by Brian K. Goss)

Pivot joints consist of the rounded end of one bone fitting into a ring formed by another bone. This structure allows rotational motion as the rounded bone moves around its axis. An example of a hinge joint is the joint of the first and second vertebrae of the neck, which allows the head to move forward and backward (Fig. 19.29). The wrist joint that allows you to rotate your palm up and down is also a pivot joint.

Figure 19.29. The neck joint that allows the head to move back and forth is an example of a rotating joint.

Condylar joints consist of an oval end of one bone that fits into an equally oval socket of another bone (Fig. 19.30). It is also sometimes called the ellipsoidal joint. This type of joint allows angular motion along two axes, as seen in the wrist and finger joints, which can move both side to side and up and down.

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The metacarpophalangeal joints of the fingers are an example of condylar joints.

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