Chapter 9 - Joints Flashcards
Describe the structural and functional classifications of joints.
A joint, also called an articulation, or arthrosis, is a point of contact between two bones, between bone and cartilage, or between bone and teeth. Structurally, joints are classified as fibrous, cartilaginous, or synovial. On the basis of function, joints are classified as synarthroses, amphiarthroses, and diarthroses.
The structural classification of joints is based on two criteria: (1) the presence or absence of a space between the articulating bones, called a synovial cavity, and (2) the type of connective tissue that binds the bones together. In fibrous joints, there is no synovial cavity, and the bones are held together by dense irregular connective tissue that is rich in collagen fibers. In cartilaginous joints, there is no synovial cavity, and the bones are held together by cartilage. In synovial joints, the bones forming the joint have a synovial cavity and are united by the dense irregular connective tissue of an articular capsule, and often by accessory ligaments.
The functional classification of joints relates to the degree of movement they permit. A synarthrosis is an immovable joint, an amphiarthrosis is a slightly movable joint, and a diarthrosis is a freely movable joint. All diarthroses are synovial joints.
Describe the 3 types of fibrous joints.
A suture is a fibrous joint composed of a thin layer of dense irregular connective tissue; sutures occur only between bones of the skull. Sutures play important roles in shock absorption in the skull. Some sutures, although present during growth of the skull, are replaced by bone in the adult. Such a suture is called a synostosis, or bony joint—a joint in which there is a complete fusion of two separate bones into one
A syndesmosis is a fibrous joint in which there is a greater distance between the articulating surfaces and more dense irregular connective tissue than in a suture. The dense irregular connective tissue is typically arranged as a bundle (ligament), allowing for limited movement.
An interosseous membrane consists of a substantial sheet of dense irregular connective tissue that binds neighboring long bones and permits slight movement (amphiarthrosis).
Describe the 3 types of cartilaginous joints.
A synchondrosis is a cartilaginous joint in which the connecting material is hyaline cartilage and is slightly movable.
A symphysis is a cartilaginous joint in which the ends of the articulating bones are covered with hyaline cartilage, but a broad, flat disc of fibrocartilage connects the bones. A symphysis is a slightly movable joint (amphiarthrosis).
Epiphyseal cartilages are actually hyaline cartilage growth centers during endochondral bone formation, not joints associated with movements. An example of epiphyseal cartilage is the epiphyseal (growth) plate that connects the epiphysis and diaphysis of a growing bone. Functionally, epiphyseal cartilage is an immovable joint (synarthrosis).
Describe the structure of synovial joints.
The unique characteristic of a synovial joint is the presence of a space called a synovial cavity or joint cavity between the articulating bones. Because the synovial cavity allows considerable movement at a joint, all synovial joints are classified functionally as freely movable (diarthroses). The bones at a synovial joint are covered by a layer of hyaline cartilage called articular cartilage. A sleeve-like articular capsule or joint capsule surrounds a synovial joint, encloses the synovial cavity, and unites the articulating bones. The articular capsule is composed of two layers, an outer fibrous membrane and an inner synovial membrane. The fibrous membrane is a thickened continuation of the periosteum between bones. The fibers of some fibrous membranes are arranged as parallel bundles of dense regular connective tissue that are highly adapted for resisting strains. The strength of these fiber bundles, called ligaments, is one of the principal mechanical factors that hold bones close together in a synovial joint. The inner layer of the articular capsule, the synovial membrane, is composed of areolar connective tissue with elastic fibers. At many synovial joints the synovial membrane includes accumulations of adipose tissue, called articular fat pads. The synovial membrane secretes synovial fluid, whose functions include reducing friction by lubricating the joint, absorbing shocks, and supplying oxygen and nutrients to and removing carbon dioxide and metabolic wastes from the chondrocytes within articular cartilage.
Many synovial joints also contain accessory ligaments called extracapsular ligaments and intracapsular ligaments. Extracapsular ligaments lie outside the articular capsule. Intracapsular ligaments occur within the articular capsule but are excluded from the synovial cavity by folds of the synovial membrane.
Inside some synovial joints, such as the knee, crescent-shaped pads of fibrocartilage lie between the articular surfaces of the bones and are attached to the fibrous capsule. These pads are called articular discs or menisci. The functions of the menisci are known to include the following: (1) shock absorption; (2) a better fit between articulating bony surfaces; (3) providing adaptable surfaces for combined movements; (4) weight distribution over a greater contact surface; and (5) distribution of synovial lubricant across the articular surfaces of the joint.
A labrum, prominent in the ball-and-socket joints of the shoulder and hip, is the fibrocartilaginous lip that extends from the edge of the joint socket. The labrum helps deepen the joint socket and increases the area of contact between the socket and the ball-like surface of the head of the humerus or femur.
Describe the structure and function of bursae and tendon sheaths.
Saclike structures called bursae are strategically situated to alleviate friction in some joints, such as the shoulder and knee joints. They are filled with a small amount of fluid that is similar to synovial fluid.
Tendon sheaths or synovial sheaths are tubelike bursae; they wrap around certain tendons that experience considerable friction as they pass through tunnels formed by connective tissue and bone. The inner layer of a tendon sheath, the visceral layer, is attached to the surface of the tendon. The outer layer, known as the parietal layer, is attached to bone. Between the layers is a cavity that contains a film of synovial fluid.
What are the 4 categories of movements that can occur at synovial joints?
Movements at synovial joints are grouped into four main categories: (1) gliding, (2) angular movements, (3) rotation, and (4) special movements, which occur only at certain joints.
Describe gliding and rotation.
Gliding is a simple movement in which nearly flat bone surfaces move back-and-forth and from side-to-side with respect to one another.
In rotation, a bone revolves around its own longitudinal axis. One example is turning the head from side to side at the atlanto-axial joint (between the atlas and axis), as when you shake your head “no.”
Describe the 7 types of angular movements.
In angular movements, there is an increase or a decrease in the angle between articulating bones. The major angular movements are flexion, extension, lateral flexion, hyperextension, abduction, adduction, and circumduction.
Flexion and extension are opposite movements. In flexion, there is a decrease in the angle between articulating bones; in extension, there is an increase in the angle between articulating bones. Lateral flexion involves lateral movement, such as bending to the side at the waist. Continuation of extension beyond the anatomical position is called hyperextension. Abduction, or radial deviation, is the movement of a bone away from the midline; adduction, or ulnar deviation is the movement of a bone toward the midline (think of swinging a leg sideways in or out). Circumduction is movement of the distal end of a body part in a circle. Circumduction is not an isolated movement by itself but rather a continuous sequence of flexion, abduction, extension, adduction, and rotation of the joint (or in the opposite order).
Describe the 11 types of special movements.
Special movements occur only at certain joints. They include elevation, depression, protraction, retraction, inversion, eversion, dorsi-flexion, plantar flexion, supination, pronation, and opposition.
Elevation is a superior movement of a part of the body, such as closing the mouth or shrugging the shoulders. Depression is an inferior movement of a part of the body, such as opening the mouth or returning shrugged shoulders to the anatomical position. Protraction is a movement of a part of the body anteriorly. Retraction is a movement of a protracted part of the body back to the anatomical position. Inversion is a turning inward of the sole medially at the intertarsal joints. Eversion is a turning outward of the sole laterally at the intertarsal joints. Dorsiflexion refers to bending of the foot at the ankle or talocrural joint in the direction of the dorsum (superior surface). Dorsiflexion occurs when you stand on your heels. Its opposing movement is plantar flexion. Plantar flexion involves bending of the foot at the ankle joint in the direction of the plantar or inferior surface, as when you elevate your body by standing on your toes. Supination is a movement of the forearm at the proximal and distal radioulnar joints in which the palm is turned anteriorly. This position of the palms is one of the defining features of the anatomical position. Its opposing movement is pronation. Pronation is a movement of the forearm in which the palm is turned posteriorly. Opposition is the movement of the thumb at the carpometacarpal joint (between the trapezium and metacarpal of the thumb) in which the thumb moves across the palm to touch the tips of the fingers on the same hand.
Describe the 6 subtypes of synovial joints.
Synovial joints are divided into six categories based on type of movement: plane, hinge, pivot, condyloid, saddle, and ball-and-socket.
The articulating surfaces of bones in a plane joint, also called a planar joint, are flat or slightly curved. Plane joints primarily permit back-and-forth and side-to-side movements between the flat surfaces of bones, but they may also rotate against one another.
In a hinge joint, or ginglymus joint, the convex surface of one bone fits into the concave surface of another bone. As the name implies, hinge joints produce an angular, opening-and-closing motion like that of a hinged door. Hinge joints, such as the knee, permit only flexion and extension.
In a pivot joint, or trochoid joint, the rounded or pointed surface of one bone articulates with a ring formed partly by another bone and partly by a ligament. Examples of pivot joints are the atlanto-axial joint, in which the atlas rotates around the axis and permits the head to turn from side-to-side as when you shake your head “no.”
In a condyloid joint or ellipsoidal joint, the convex oval-shaped projection of one bone fits into the oval-shaped depression of another bone. A condyloid joint is biaxial because the movement it permits is around two axes (flexion–extension and abduction–adduction), plus limited circumduction.
In a saddle joint or sellar joint, the articular surface of one bone is saddle-shaped, and the articular surface of the other bone fits into the “saddle” as a sitting rider would sit. The movements at a saddle joint are the same as those at a condyloid joint: biaxial (flexion–extension and abduction–adduction) plus limited circumduction.
A ball-and-socket joint or spheroid joint consists of the ball-like surface of one bone fitting into a cuplike depression of another bone. Such joints are triaxial (multiaxial), permitting movements around three axes (flexion–extension, abduction–adduction, and rotation).
Describe the anatomical components of the temporomandibular joint and explain the movements that can occur at this joint.
The temporomandibular joint (TMJ) is a combined hinge and plane joint formed by the condylar process of the mandible and the mandibular fossa and articular tubercle of the temporal bone. The temporomandibular joint is the only freely movable joint between skull bones. In the temporomandibular joint, the mandible may function in depression (jaw opening) and elevation (jaw closing), and protraction, retraction, lateral displacement, and slight rotation.
Describe the anatomical components of the shoulder joint and the movements that can occur at this joint.
The shoulder joint is a ball-and-socket joint formed by the head of the humerus and the glenoid cavity of the scapula. The shoulder joint allows flexion, extension, hyperextension, abduction, adduction, medial rotation, lateral rotation, and circumduction of the arm. Although the ligaments of the shoulder joint strengthen it to some extent, most of the strength results from the muscles that surround the joint, especially the rotator cuff muscles.
Describe the anatomical components of the elbow joint and the movements that can occur at this joint.
The elbow joint is a hinge joint formed by the trochlea and capitulum of the humerus, the trochlear notch of the ulna, and the head of the radius. The elbow joint allows flexion and extension of the forearm.
Describe the anatomical components of the hip joint and the movements that can occur at this joint.
The hip joint (coxal joint) is a ball-and-socket joint formed by the head of the femur and the acetabulum of the hip bone. The hip joint allows flexion, extension, abduction, adduction, lateral rotation, medial rotation, and circumduction of the thigh.
Describe the main anatomical components of the knee joint and explain the movements that can occur at this joint.
The knee joint (tibiofemoral joint) is the largest and most complex joint of the body. It is a modified hinge joint (because its primary movement is a uniaxial hinge movement) that consists of three joints within a single synovial cavity.
The knee joint allows flexion, extension, slight medial rotation, and lateral rotation of the leg in the flexed position.
