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