By the end of this section, girlfriend will have actually completed the complying with objectives:Classify the different varieties of joints ~ above the communication of structureExplain the role of joints in skeleton movement
The allude at which 2 or an ext bones accomplish is referred to as a joint, or articulation. Joints are responsible for movement, such together the activity of limbs, and stability, such as the stability discovered in the skeleton of the skull.
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Classification of Joints on the basis of Structure
There room two methods to classify joints: ~ above the basis of their structure or ~ above the basis of their function. The structural group divides joints right into bony, fibrous, cartilaginous, and synovial joints depending on the product composing the joint and also the presence or absence of a cavity in the joint.
Figure 2. Gomphoses space fibrous joints in between the teeth and also their sockets. (credit: alteration of work by Gray’s Anatomy)
Cartilaginous joints room joints in which the skeletal are associated by cartilage. There space two varieties of cartilaginous joints: synchondroses and symphyses. In a synchondrosis, the bones room joined by hyaline cartilage. Synchondroses are found in the epiphyseal key of growing bones in children. In symphyses, hyaline cartilage covers the finish of the bone but the connection between bones occurs v fibrocartilage. Symphyses are found at the joints in between vertebrae. Either kind of cartilaginous joint allows for very small movement.
Figure 3. Synovial joints space the just joints that have a an are or “synovial cavity” in the joint.
Synovial joints room the just joints that have a room between the adjoining bones (Figure 3). This space is referred to as the synovial (or joint) cavity and also is filled v synovial fluid. Synovial fluid lubricates the joint, reducing friction in between the skeletal and enabling for better movement. The end of the bones space covered v articular cartilage, a hyaline cartilage, and also the whole joint is surrounding by one articular capsule created of connective tissue that enables movement that the share while resisting dislocation. Articular capsules may also possess ligaments that organize the bones together. Synovial joints are qualified of the best movement the the three structural share types; however, the more mobile a joint, the weaker the joint. Knees, elbows, and also shoulders are examples of synovial joints.
Classification the Joints ~ above the basis of Function
The functional category divides joints into three categories: synarthroses, amphiarthroses, and also diarthroses. A synarthrosis is a joint the is immovable. This contains sutures, gomphoses, and synchondroses. Amphiarthroses room joints that permit slight movement, including syndesmoses and also symphyses. Diarthroses room joints that enable for complimentary movement of the joint, as in synovial joints.
Movement at Synovial Joints
The wide selection of movement permitted by synovial joints produce different varieties of movements. The movement of synovial joints deserve to be classified as among four different types: gliding, angular, rotational, or one-of-a-kind movement.
Gliding movements take place as relatively flat bone surfaces relocate past each other. Gliding movements produce very little rotation or angular activity of the bones. The joints the the carpal and also tarsal bones are examples of joints that develop gliding movements.
Angular movements are produced when the angle in between the bones of a joint changes. Over there are several different varieties of angular movements, including flexion, extension, hyperextension, abduction, adduction, and also circumduction. Flexion, or bending, occurs once the angle in between the skeleton decreases. Moving the forearm increase at the elbow or relocating the wrist to move the hand towards the forearm are examples of flexion. Extension is the opposite of flexion in that the angle between the bones of a share increases. Straightening a limb after flexion is an example of extension. Expansion past the regular anatomical position is referred to as hyperextension. This consists of moving the neck back to look at upward, or bending the wrist so the the hand moves far from the forearm.
Abduction occurs when a bone moves far from the midline of the body. Examples of kidnapping are relocating the arms or legs laterally to lift them directly out come the side. Adduction is the motion of a bone toward the midline of the body. Motion of the limbs inward after ~ abduction is an instance of adduction. Circumduction is the motion of a body in a one motion, together in moving the arm in a one motion.
Rotational movement is the movement of a bone as it rotates roughly its longitudinal axis. Rotation can be towards the midline of the body, i beg your pardon is described as medial rotation, or far from the midline the the body, i m sorry is described as lateral rotation. Movement of the head from side to next is an instance of rotation.
Some movements that can not be classified as gliding, angular, or rotational are referred to as special movements. Inversion requires the soles the the feet moving inward, toward the midline that the body. Eversion is the contrary of inversion, movement of the single of the foot outward, away from the midline the the body. Protraction is the anterior motion of a bone in the horizontal plane. Retraction occurs as a share moves ago into place after protraction. Protraction and retraction can be viewed in the motion of the mandible as the jaw is thrust outwards and then earlier inwards. Elevation is the movement of a bone upward, such as when the shoulders space shrugged, lifting the scapulae. Depression is opposing of elevation—movement downward of a bone, such together after the shoulders room shrugged and the scapulae return to their normal position from one elevated position. Dorsiflexion is a bending at the fish eye such the the toes room lifted toward the knee. Plantar flexion is a bending at the ankle once the heel is lifted, together as when standing top top the toes. Supination is the movement of the radius and also ulna skeletal of the forearm so that the palm faces forward. Pronation is the contrary movement, in i beg your pardon the palm faces backward. Opposition is the movement of the thumb toward the finger of the very same hand, making it feasible to grasp and hold objects.
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Types that Synovial Joints
Synovial joints are further classified right into six various categories ~ above the basis of the shape and structure that the joint. The form of the share affects the form of movement permitted by the share (Figure 4). These joints can be described as planar, hinge, pivot, condyloid, saddle, or ball-and-socket joints.