Chapter 8: Joints

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Joints

or articulations, are sites where 2 or more bones meet, weakest part of the skeleton, classified by structure and function. Less movable joints are more stable

Structural Classification of Joints

focuses on the material binding the bones together and whether or not a joint cavity is present. There are fibrous, cartilaginous, and synovial joints

Functional Classification of Joints

based on the amount of movement allowed at the joint

Synarthroses

immovable joints (ex: fibrous joints)

Amphiartroses

slightly movable joints, mostly in axial skeleton

Diarthroses

freely movable joints, predominate in the limbs (ex: synivial joints)

Fibrous Joints

bones are joined by fibrous tissue, namely dense fibrous connective tissue, and no joint cavity is present, mostly immovable. 3 types of fibrous joints (sutures, syndesmoses,and gomphoses)

Sutures

seams; occur only between bones of the skull, Rigid, interlocking joints containing short connective tissue fibers
Allow for growth during youth, In middle age, sutures ossify and are called synostoses

Syndesmoses

bones are connected by ligaments, cords, or bands of fibrous tissue, Movement varies from immovable to slightly movable and depends on length and amount of fibers

Gomphoses

(gomphosis)a peg-in-socket fibrous joint (ex: articulation of a tooth with its bony alveolar socket), Fibrous connection is the periodontal ligament

Catilaginous Joints

the articulating bones are united by cartilage, they lack joint cavity and not highly movable, 2 types of cartilaginous joints are synchondroses and symphyses

Synchondroses

(synchondrosis)site where bar or plate of hyaline cartilage unites bone (ex: epiphyseal plate in children and coastal cartilage of first rib and manibrium of sternum)

Symphyses

articlar surfaces of the bones are covered with articular (hyaline) cartilage, and is fused to an intervening pad of fibrocartilage [acts as shock absorber cause resiliency], strong flexible amphiathroses

Synovial Joints

those in which the articulating bones are seperated by a fluid-containing joint cavity. All are diarthrotic, Include all limb joints; most joints of the body. 6 distinguishing features

1. Articular Cartilage

Glassy-smooth hylaine cartilage covers the opposing bone surfaces

2. Joint Cavity

a feature unique to synovial joints, space that contains small amount of synovial fluid

3. Articular Capsule

2 layers enclose the joint cavity. External layer is tough fibrous capsule (composed of dense irregular connective tissue) [strenghtens joint so that bones are not pulled apart. Inner layer is a synovial membrane (composed of loose connective tissue) [covers all internal joint surfaces that are not hyaline cartilage]

4. Synovial Fluid

slippery fluid which occupies all free spaces within the joint capsule. Lubricates joint surfaces and nurishes articular cartilage.

5. Reinforcing Ligaments

reinforce and strengthen synovial joints. Most often they are capsular, or intristic, ligaments [thickened part of fibrous capsule], Extracapsular (outside capsule) or Intracapsular (deep to capsule; covered by synovial membrane)

Nerves and Blood Vessels

Nerve fibers detect pain, monitor joint position and stretch, Capillary beds produce filtrate for synovial fluid

Bursae

Flattened, fibrous sacs lined with synovial membranes , Contain synovial fluid, Commonly act as "ball bearings" where ligaments, muscles, skin, tendons, or bones rub together

Tendon Sheath

Elongated Bursa that wraps completely around a tendon

Factors influencing Stability of Synovial Joints

shapes of the articular sirface, the number and positioning of ligaments, and muscle tone

Articular Surfaces

determines what movements are possible at a joint (minor role)

Ligaments

unite the bones and prevent excessive or undesirable motion (more ligaments joint have the stronger)

Muscle Tone

which keeps tendons that cross the joint taut, extremely important in reinforcing the shoulder and knee joints and the arches of the foot

Origin

attachment of muscle to the immovable (or less movable bone)

Insertion

attachment of muscle to the movable bone [Muscle contraction causes the insertion to move toward the origin; Movements occur along transverse, frontal, or sagittal planes]

Nonaxial Movement

slipping movements only

Uniaxial Movement

movement in one plane

Biaxial Movement

movement in two planes

Multiaxial Movement

movement in or around all three planes of space and axes

Table 8.2 (cont.)

Table 8.2 (cont.) [2]

Table 8.2 (cont.) [3]

Gliding Movements

simplest joint movements, occurs when one flat, or nearly flat, bone surface glides or slips over another (Intercarpal joints
Intertarsal joints
Between articular processes of vertebrae)

Angular Movements

increase or decrease the angle between two bones (flexion, extesnion, abduction, aduction, circumduction)

Flexion

bending movement along sagittal plane, that decrease the angle of the joint, and brings articulating bones closer together

Extension

reverse of flexion and occurs at the same joints, invloves movement along the sagittal plane that increases angle between articulating bones, typically straight [Hyperextension - excessive extension beyond anatomical position]

Abduction

movement of limb away from the midline or median plane of the body, along the frontal plane

Adduction

opposite of abduction, movement of a limb toward the body midline, or midline of hand or foot.

Circumduction

moving a limb so that it describes a cone in space

Rotation

turning of a bone around its own long axis. Medial and lateral rotation (Between C1 and C2 vertebrae
Rotation of humerus and femur)

Special Movements

movements which don't fit into any of the above catergories

Supination

turning backward, rotating forearm laterally so that the palm faces anteriorly or superiorly

Pronation

turning forward, forearm rotates medially and the palm faces posteriorly or interiorly

Dorsiflexion

lifting the foot so that its superior surface approaches the skin

Plantar Flexion

pointing the toe

Inversion

sole of the foot turns medially

Eversion

sole of the foot faces laterally

Protraction

Nonangular anterior movements in a transverse plane, (ex: jut out jaw)

Retraction

Nonangular posterior movements in a transverse plane (ex: retracted jaw when brought back)

Elevation

lifitng a body part superiorly

Depression

moving elevated part inferiorly

Opposition

movement of saddle joint betwenn metacarpal 1 and the trapezium of thumb

Types of Synovial Joints

Plane, Hinge, Pivot, Condyloid, Saddle, Ball-and Socket

(Synovial) Plane Joints

articular surfaces are flat and allow only short nonaxial gliding movements

(Synovial) Hinge Joints

the cylindrical end of one bone conforms to a tough-shaped surface on another, motion is along a single plane and reselbles that of a mehanical hinge

(Synovial) Pivot Joints

the rounded end of one bone conforms to a "sleeve" or ring composed of bone (and possibly ligaments) of another, only movement allowed is uniaxial rotation of one bone around its own long axis

(Synovial) Condyloid Joints

(ellipsoidal joints) the oval articular surface of one bone fits into a complementary depression in another. Important characteristic is that both articulating surfaces are oval. Permits all angular motions

(Synovial) Saddle Joints

resemble condyloid joints, but they allow greater freedom of movement. Each articular surface has both concave and convex areas.

(Synovial) Ball-and-Socket Joints

the spherical or hemispherical head of one bone articulates with the cuplike socket of another. These joints are multiaxial and the most freely moviing synovial joints.

Knee Joint

the largest and most complex joint in the body, conisists of three joints

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