Articulations or joints

Sight where two or more bones meet

Functions of joints

Gives skeleton mobility and holds skeleton together

Classifications

Functional equals amount of movement allowed

Structural equals material binding bones together

Functional classification joints

based on amount of movement joint allows

three functional classifications

1) Synarthroses = Immovable joints

2) Amphiarthroses = slightly moveable joints

3) Diarthroses = Freely moveable joints

(The less movable a joint the more stable it is going to be)

Structural classification of joints

Based on materials joining bones together

Presence / absence of joint cavity

3 structural classifications

1) Fibrous Joints

2) Cartilaginous joints

3) Synovial joints

Fibrous joints

bones joined by collagen fibers of connective tissue

no joint cavity

most synarthrotic

depends on length on C.T. fibers

trhee types

1) sutures

2) syndesmoses

3) gomphoses

Sutures = seams

rigid interlocking joints

short connective tissue fibers (continuous with periosteum)

allowed for growth of skull during youth

suture ossify and fuse in middle age (now termed synostoses)

immovable joint for protection of brain

syndesmoses

bones connected exclusively by ligaments, cords or bands of fibrous tissue

fiber length varies

amount of movement depends on fiber length

shorter fibers = less movement (in any)

typically considered synarthroses

gomphoses (tooth)

peg in socket fibrous joint

teeth in alveolar sockets

periodontal ligaments: short, fibrous connection

synarthrotic

Cartilaginous joints

bones united by cartilage

no joint cavity

not highly movable

two types:

1) synchondroses

2) symphyses

cartilaginous joints: synchondroses

bar/plate of hyaline cartilage joins bones

(temporary epiphyseal plate joints (become synostoses after plate closure), cartilage of first rib with manubrium)

virtually all are synarthrotic

cartilaginous joints: symphyses

"pads of cartilage"

fibrocartilage joins bones (hyaline cartilage is present as articular cartilage)

strong, flexible amphiarthroses

synovial joints

bones separated by fluid-filled joint cavity

all are diarthrotic (freely movable)

include virtually all limb joints; most joints of body

synovial joints: general structure

articular cartilage: hyaline cartilage

absorbs compressive forces

prevents crushing of bone ends

Joint cavity:

unique to synovial joints

small fluid filled potential space

expands with fluid accumulation (inflammation)

Articular capsule: two layers

1) external fibrous layer

a. dense irregular connective tissues

b. continuous with periosteum

2) inner synovial membrane

a. loose connective tissue

b. makes synovial fluid

Synovial fluid: viscous, slippery fluid formed from plasma filtrate and hyaluronic acid (consistency of egg whites)

lubricates and nourishes the articular cartilage

weeping lubrication: fluid released with cartilage compression, seeps back in to cartilage when compression is removed

contains phagocytic cells to remove debris and microbes

reinforcing ligaments (bone to bone link)

a. capsular ligaments (thickened part of fibrous layer of the articular capsule)

b. extracapsular ligaments (dee to the capsule; covered by synovial membrane

synovial joints: general structure cont.

nerves and blood vessels (nerve fibers; some detect pain, most monitor joint position and stretch)

(also capillary beds supply filtrate for synovial fluid formation)

other features found in some synovial joints

fatty pads (cushions between fibrous layer and synovial membrane or bone)

articular discs (menisci) (fibrocartilage separates articular surfaces to improve the "fit" of bone ends, stabilize joint, and reduce wear and tear

Structures associated with synovial joints

Bursae = act as "ball bearing" (sacs lined with synovial membrane, containing thin film or synovial fluid)

reduce friction where ligaments, muscles, skin, tendons, or bones rub together

Tendon sheaths = elongated bursa wrapped completely around a tendon subjected to friction

common where several tendons are crowded together

shapes of articular surfaces

determine movements allowed at the joint

minor contribution to joint stability

large, snug fitting surfaces offer more stability (hip joint: ball in a deep socket)

ligament number and location - limited role

stretched ligaments alone = not very stable

joints stabilized by ligaments alone = ??

more ligaments = stronger joint

stability of synovial joints

muscle tone = muscle tendons that cross joint are most important factor in joint stability

tension created by muscle tone keeps tendon tout

important for reinforcing shoulder joint, knee joint, and arches of foot

movement at synovial joints

muscles attach to bone or connective tissue at two points

(origin: attachment to immovable bone

insertion = attachment to movable bone)

as muscle contracts insertion moves closer to origin

muscles contract across a joint to create movement at the joint

movement occurs along the planes

movement of synovial joints: range of motion

nonaxial = slipping movement only

uniaxial = movement in one plane

biaxial = Movement can occur in two planes

multiaxial = movement in or around all three planes

general types of movement

gliding, angular and rotation

gliding

one flat bone surface glides or slips over another similar surface

example:

intercarpal joints

intertarsal joints

between articular processes of vertebrae

angular movements

increase/decrease the angle between the bones

movement along the sagittal plane

flexion = decreases angle of the joint

extension = increases angel of the joint

hypertension = excessive extension beyond anatomical position

Movement along frontal plane

abduction: movement away from midline

adduction: movement toward the midline

circumduction

involves flexion, abduction extension, and adduction of limb

movement forms a cone in space

rotation

turning of bone around its own long axis

medial rotation = anterior surface of the bone toward the midline

lateral rotation = anterior surface of the bone away from the midline

examples : between C1 and C2 vertebrae

rotation of femur and humerus

supernation an pronation of radius and ulna

refer to movement of radius around ulna

Dorsiflexion and plantar flexion of foot

movement in the transverse plane

moving a bone anteriorly and posteriorly

opposition of thumb = movement used to touch the thumb to tips of the other fingers on the same hand

small ruff elevation

tubercle

promant linear elevation

prominent crest

ramus

bar shaped bone

what occurs in zone of proliferation =

rapid division of cells

appositional

process of adding cartilage on top of preexisting cartilage

example of a short bone

carpals

internal layer of periosteum purpose

osteogenic cells