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Chapter 9: Articulations, Study notes of Human Biology

Joints can be divided into functional groups: - Synarthroses, or immovable joints, are bound together by fibrous or cartilaginous connections, which may ...

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Chapter 9: Articulations
The body is adapted to movement, which occurs only at joints where 2 bones
connect (articulations). Joints have different structures that determine the
direction and distance they can move. Joints always compromise strength to
increase mobility.
I. The Classification of Joints, p. 259
Objectives
1. The major categories of joints, and the structure and function of each category.
2. The basic structure of a synovial joint, the common accessory structures and their
functions.
The distance and direction a joint can move is called range of motion. Joints can
move a little (amphiarthrosis), a lot (diarthrosis) or not at all (synarthrosis).
Table 9-1
Functional classification
Joints can be divided into functional groups:
- Synarthroses, or immovable joints, are bound together by fibrous or
cartilaginous connections, which may fuse over time.
- Amphiarthroses, or slightly moveable joints, may have fibrous or cartilaginous
connections.
- Diarthroses, or synovial joints, are freely moveable, and are subdivided by type
of motion.
Table 9-2
Structural Classification
Joints can also be classified by structure:
- bony
- fibrous
- cartilaginous
- synovial
Synarthroses (Immovable Joints), p. 260
Synarthroses are very strong. At a synarthrosis, the edges of the bones may touch
or interlock. The 4 types of synarthrotic joints are:
1. suture:
- bones are interlocked and bound by dense fibrous connective tissue
- found only in the skull
2. gomphosis:
- a fibrous connection (periodontal ligament)
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Chapter 9: Articulations

  • The body is adapted to movement, which occurs only at joints where 2 bones connect (articulations). Joints have different structures that determine the direction and distance they can move. Joints always compromise strength to increase mobility. I. The Classification of Joints, p. 259 Objectives
  1. The major categories of joints, and the structure and function of each category.
  2. The basic structure of a synovial joint, the common accessory structures and their functions. ♣ The distance and direction a joint can move is called range of motion. Joints can move a little (amphiarthrosis), a lot (diarthrosis) or not at all (synarthrosis). Table 9- Functional classification ♣ Joints can be divided into functional groups:
  • Synarthroses, or immovable joints , are bound together by fibrous or cartilaginous connections, which may fuse over time.
  • Amphiarthroses, or slightly moveable joints , may have fibrous or cartilaginous connections.
  • Diarthroses, or synovial joints, are freely moveable , and are subdivided by type of motion. Table 9- Structural Classification ♣ Joints can also be classified by structure:
  • bony
  • fibrous
  • cartilaginous
  • synovial Synarthroses (Immovable Joints), p. 260 ♣ Synarthroses are very strong. At a synarthrosis, the edges of the bones may touch or interlock. The 4 types of synarthrotic joints are:
  1. suture:
  • bones are interlocked and bound by dense fibrous connective tissue
  • found only in the skull
  1. gomphosis:
  • a fibrous connection ( periodontal ligament )
  • binds teeth to sockets
  1. synchondrosis:
  • a rigid cartilaginous bridge between 2 bones
  • e.g. the epiphyseal cartilage of long bones
  • e.g. the connection between vertebrosternal ribs and the sternum
  1. synostosis:
  • fused bones, immovable
  • e.g. the metopic suture of the skull
  • e.g. epiphyseal lines of long bones Amphiarthroses (Slightly Moveable Joints), p. 260 ♣ An amphiarthrosis is more moveable than a synarthrosis, and stronger than a freely movable joint. ♣ The 2 major types of amphiarthrotic joints are:
  1. syndesmosis: bones connected by ligaments
  2. symphysis: bones separated by fibrocartilage Diarthroses (Moveable Joints), p. 260 ♣ Diarthroses (synovial joints) are found at the ends of long bones, within articular capsules lined with synovial membrane. ♣ The articulating surfaces of the bones within the articular capsules are padded with articular cartilages, which prevent the bones from touching. The smooth surfaces are lubricated by synovial fluid to reduce friction. ♣ Synovial fluid (which contains slippery proteoglycans secreted by fibroblasts) has 3 main functions:
  3. lubrication
  4. nutrient distribution
  5. shock absorption ♣ Synovial joints have several kinds of accessory structures:
  6. Cartilages and fat pads cushion the joint.
  • a fibrocartilage meniscus or articular disc lies between bones and may subdivide a synovial cavity.
  • fat pads superficial to the joint capsule protect articular cartilages
  1. Various kinds of accessory ligaments support and strengthen joints.
  • an injury which tears collagen fibers in a ligament is a sprain
  1. Tendons attached to muscles around a joint help support the joint.
  2. Bursae are pockets of synovial fluid that cushion areas where tendons or ligaments rub. ♣ Several factors stabilize joints and prevent injury by limiting range of motion:
  • in the anterior-posterior plane
  • reduces the angle between elements extension:
  • in the anterior-posterior plane
  • increases the angle between elements hyperextension:
  • extension past anatomical position Figure 9-3b,c abduction:
  • in the frontal plane
  • moves away from the longitudinal axis of the body adduction:
  • in the frontal plane
  • moves toward the longitudinal axis of the body Figure 9-3d circumduction:
  • a circular motion without rotation
    1. Rotational Motions Figure 9- rotation: the direction of a rotation from anatomical position, relative to the longitudinal axis of the body.
  • left or right rotation
  • medial rotation ( inward rotation ): rotates toward the axis
  • lateral rotation ( outward rotation ): rotates away from the axis
  • pronation: rotates the forearm, radius over ulna
  • supination: the forearm in anatomical position
    1. Special movements of specific articulations: Figure 9-5a inversion: twists the sole of the foot medially eversion: twists the sole of the foot laterally Figure9-5b dorsiflexion: flexion at the ankle (lifting toes) plantar flexion: extension at the ankle (pointing toes) Figure9-5c opposition: movement of the thumb toward fingers or palm (grasping) Figure 9-5d protraction: moves a body part anteriorly, in the horizontal plane (pushing

forward) retraction: the opposite of protraction, moving anteriorly (pulling back) Figure 9-5e elevation: moves in a superior direction (up) depression: moves in an inferior direction (down) Figure 9-5f lateral flexion: bends the vertebral column from side to side. A Structural Classification of Synovial Joints, p. 267

  • Synovial joints may be classified by the shapes of their articulating surfaces, as follows: Figure 9-6 a
  1. gliding joints:
  • flattened or slightly curved faces
  • limited motion (nonaxial) Figure 9-6 b
  1. hinge joints:
  • angular motion in a single plane (monaxial) Figure 9-6 c
  1. pivot joints:
  • rotation only (monaxial) Figure 9-6 d
  1. ellipsoidal joints:
  • an oval articular face within a depression
  • motion in 2 planes (biaxial) Figure 9-6 e
  1. saddle joints:
  • two concave faces, straddled (biaxial) Figure 9-6 f
  1. ball-and-socket joints:
  • a round articular face in a depression (triaxial) Key A joint can’t be both highly mobile and very strong. The greater the mobility, the weaker the joint, because mobile joints rely on muscular and ligamentous support rather than solid bone-to-bone connections.

The Shoulder Joint, p. 272 Figure 9-

  • The shoulder joint ( glenohumeral joint ) allows more motion than any other joint. Therefore, it is also the least stable.
  • The shoulder joint is a ball-and-socket diarthrosis between the head of the humerus and the glenoid cavity of the scapula. The socket of the glenoid cavity is deepened by a lining of fibrocartilage (the glenoid labrum) that extends past the bone.
  • The acromion of the clavicle and the coracoid process of the scapula project laterally, superior to the humerus, and help stabilize the joint, but position is maintained mainly by skeletal muscles, tendons and ligaments ( glenohumeral , coracohumeral , coracoacromial , coracoclavicular , and acromioclavicular ligaments).
  • A common injury is partial or complete dislocation of the shoulder joint (shoulder separation).
  • The main support for the shoulder joint is a muscle group called the rotator cuff ( supraspinatus , infraspinatus , subscapularis and teres minor muscles).
  • The shoulder has several important bursae that reduce friction across the joint (the subacromial , subcoracoid , subdeltoid and subscapular bursae). The Elbow Joint, p. 273 Figure 9-
  • The elbow is a stable hinge joint with articulations between the humerus, radius and ulna.
  • The largest articulation is the humeroulnar joint (trochlea of humerus with the trochlear notch of ulna) which has a limited degree of movement. The smaller articulation (between the capitulum of the humerus and head of radius) is the humeroradial joint.
  • Elbow motion is controlled by the biceps brachii muscle (attached to the radial tuberosity), and stabilized by several ligaments (the radial collateral , annular , and ulnar collateral ligaments). The Hip Joint, p. 274 Figure 9-
  • The hip joint ( coxal joint ) is a strong ball-and-socket diarthrosis with a wide range of motion.
  • The head of the femur fits into the socket of the acetabulum, which is extended by a fibrocartilage rim ( acetabular labrum ).
  • The strong articular capsule is reinforced by several ligaments (including the iliofemoral , pubofemoral , ischiofemoral , and transverse acetabular ligaments, and the ligamentum teres ) and supported by large muscles.
  • The hip joint is very stable. Stress on the angle of the neck tends to cause fractures rather than dislocations. The Knee Joint, p. 275 Figure 9-
  • The knee joint is a complicated hinge joint, transferring weight from the femur to the tibia. It has 2 femur-tibia articulations (at the medial and lateral condyles) and 1 between the patella and the patellar surface of the femur.
  • The 2 femur-tibia articulations are cushioned by fibrocartilage pads (the medial and lateral menisci), which stabilize the joint and give lateral support. Fat pads and bursae also protect the joint.
  • 7 major ligaments support the knee joint:
  • patellar ligament (anterior, contains the patella)
  • 2 popliteal ligaments (posterior)
  • anterior and posterior cruciate ligaments (inside the joint capsule)
  • tibial collateral ligament (medial)
  • fibular collateral ligament (lateral)
  • Standing with legs straight “locks” the knees by jamming the lateral meniscus between the tibia and femur. Table 9-4 summarizes the articulations of the appendicular skeleton. IV. Aging and Articulations, p. 278 Objective
  1. Describe the effect of aging on articulations, and discuss the most common clinical problems that develop as a result.
  • Rheumatism is the general term for pain and stiffness of the skeletal and muscular systems.
  • Arthritis specifically includes all forms of rheumatism that damage the articular cartilages of the synovial joints:
  • osteoarthritis , caused by wear and tear of joint surfaces or genetic factors affecting collagen formation, generally affects people over age 60.

(gliding, flexion, extension, hyperextension, abduction, adduction, circumduction, rotation, pronation, supination, inversion, eversion, dorsiflexion, plantar flexion, opposition, protraction, retraction, depression, elevation, and lateral flexion)

  • the 6 structural types of synovial joints (gliding, hinge, pivot, ellipsoidal, saddle, and ball-and-socket)
  • the structures and movements of: intervertebral articulations
  • the structures and movements of the shoulder joint
  • the structures and movements of the elbow joint
  • the structures and movements of the hip joint
  • the structures and movements of the knee joint
  • the effects of aging on joints
  • the relationship of the skeletal system to other body systems