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The October Classic
Vs.
But for those that hate the Bosox, watch this…
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Joints (Articulations)
Weakest parts of the skeleton
Articulation – site where two or more bones meet
Functions of joints
Give the skeleton mobility
Hold the skeleton together
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Classification of Joints: Structural
Structural classification focuses on the material
binding bones together and whether or not a joint
cavity is present
The three structural classifications are:
Fibrous: immobile
Cartilaginous: rigid and moveable examples
Synovial: freely moveable
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Classification of Joints: Functional
Functional classification is based on the amount of
movement allowed by the joint
The three functional classes of joints are:
Synarthroses – immovable joint (axial skeleton)
Amphiarthroses – slightly movable joint (axial
skeleton)
Diarthroses – freely movable joint (limbs)
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Summary of Joint Classes
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Fibrous Structural Joints
The bones are joined by fibrous tissues
There is no joint cavity
Most are immovable
There are three types:
Sutures
Syndesmoses
Gomphoses
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Fibrous Structural Joints: Sutures
Occur between the bones of the skull
Comprised of interlocking junctions completely filled with
connective tissue fibers
Bind bones tightly together, but allow for growth during youth
In middle age, skull bones fuse and are called synostoses
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Fibrous Structural Joints: Syndesmoses
Bones are connected by a fibrous tissue ligament
Movement varies from immovable to slightly variable
Examples include the connection between the tibia and fibula,
and the radius and ulna
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Fibrous Structural Joints: Gomphoses
The peg-in-socket fibrous joint between a tooth and its alveolar
socket
The fibrous connection is the periodontal ligament
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Cartilaginous Joints
Articulating bones are united by cartilage
Lack a joint cavity
Two types – synchondroses and symphyses
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Cartilaginous Joints: Synchondroses
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Figure 8.2a, b
Cartilaginous Joints: Synchondroses
A bar or plate of hyaline cartilage unites the bones
All synchondroses are synarthrotic
Examples include:
Epiphyseal plates of children (eventually become synostoes)
Joint between the costal cartilage of the first rib and the menubrium of
the sternum
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Cartilaginous Joints: Symphyses
Hyaline cartilage covers the articulating surface of the bone and is fused to
an intervening pad of fibrocartilage
Amphiarthrotic joints designed for strength and flexibility
Examples include intervertebral joints and the pubic symphysis of the pelvis
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Synovial Joints
Those joints in which the articulating bones are separated by a fluidcontaining joint cavity
All are freely movable diarthroses
Examples – all limb joints, and most joints of the body
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Synovial Joints: General Structure
Synovial joints all have the following 5 features:
Articular cartilage:
Hyaline cartilage covers the opposing bone surfaces
Absorbs compression
Joint (synovial) cavity:
Space that contains a small amount of synovial fluid
Articular capsule:
Encloses the joint cavity
External layer (fibrous capsule) composed of dense irregular
connective tissue that is continuous w/ periostea of the
articulating bones
Strengthens joint so bones are not pulled apart
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Synovial Joints: General Structure
Synovial fluid
Occupies all free spaces within the joint capsule
Weight bearing film that reduces friction between cartilage
surfaces
Weeping lubrication: weeps out, seeps back in (when under
compression)
Contains phagocytes: remove cellular debris
Reinforcing ligaments
Capsular or intrinsic ligaments that are thickened parts of the
fibrous capsule
Extra-/intra-capsular ligaments
Richly supplied with sensory nerve endings that monitor the
joint’s position
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Table 8.2.1
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Table 8.2.2
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Table 8.2.3
Synovial Joints: Friction-Reducing Structures
“Bags of Lubricant” that reduce friction & found between adjacent structures
Bursae – flattened, fibrous sacs lined with synovial membranes and
containing a film of synovial fluid
Common where ligaments, muscles, skin, tendons, or bones rub together
Tendon sheath – elongated bursa that wraps completely around a tendon
subjected to friction
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Synovial Joints: Factors influencing the stability of
synovial joints
Stability is determined by:
i) Shape of the articular surfaces
ii) Number and positions of ligaments
iii) Quality of muscle tone
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Synovial Joints: Factors influencing the stability of
synovial joints
i) Shape of the articular surfaces:
Play minor role in joint stability
Ball & socket very stable
Shallow socket or no socket, unstable
ii) Ligaments:
The more, the stronger (stabler)
Stretched ligaments stay stretched
When the joint is braced only by ligaments, the joint is not stable
ii) Muscle tone:
Muscle tendons that cross the joint are the most important stabilizing factor
Tendons are kept tight at all times by the tone of the muscle
(tone = low level of contractile activity)
E.g. most important for shoulder and knee joints, and the arch of the foot
So what’s good and bad muscle tone…?
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Good Muscle Tone…
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And Bad Muscle Tone
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Synovial Joints: Movement (see Table 8.2)
Every skeletal muscle is attached to at least 2
points:
Origin – attachment to the immovable (or less
movable) bone
Insertion – attachment to the movable (or more
movable) bone
Thus, body movement occurs during contraction of
muscle across joints & their insertion moves
toward their origin.
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Synovial Joints: Range of Motion
Nonaxial movement: no axis, slipping movements
Uniaxial movement: movement in one plane
Biaxial movement: movement in two planes
Multiaxial movement: movement in or around all
three planes
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Range of Motion
There are 3 types of movements:
Gliding
Angular movements
Rotation
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Gliding Movements
Translation: One flat bone surface glides or slips
over another similar surface without angulation or
rotation
Examples – intercarpal and intertarsal joints, and
between the flat articular processes of the vertebrae
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Gliding Movement
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Figure 8.5a
Angular Movement
Increase or decrease the angle between 2 bones. Include:
Flexion — bending movement along the sagittal plane that
decreases the angle of the joint and brings the articular
bones closer together
Extension — (reverse of flexion) bending movement along
the sagittal plane that increases the angle of the joint and
brings the articular bones further apart
Hyperextension – bending beyond upright (or normal)
extension
Dorsiflexion (toes up) and plantar flexion (pointing toes)
of foot
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Angular Movement
Abduction — (moving away) movement of limb
away from the midline / or median plane of body
along the frontal plane
Adduction — (moving toward) movement of a
limb toward the body midline
Circumduction — moving a limb so that it
describes a cone in space
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Angular Movement
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Figure 8.5b
Angular Movement
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Figure 8.5c, d
Angular Movement
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Figure 8.5e, f
Rotation
Turning a bone along its own long axis
E.g. 1st two cervical vertebrae
E.g. hip and shoulder joints
Medial rotation: toward median plane
Lateral rotation: away from median plane
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Rotation
The turning of a bone
around its own long axis
Examples
Between first two
vertebrae
Hip and shoulder joints
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Figure 8.5g
Special Movements
Supination and pronation:
Supination: (turning backwards) e.g. palm up or forward (or palm
superiorly or anteriorly
Pronation: (turning forwards) e.g. palm down or back (or palm
inferior or posterior)
Eg. For supination/pronation is the radius and ulna
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Special Movements
Inversion and eversion: e.g. the foot
Inversion: the sole of the foot moves medially
Eversion: the sole of the foot moves laterally
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Special Movements
Protraction and retraction: e.g. the jaw
Nonangular anterior (protraction) and posterior
(retraction) movements in a transverse plane
Or…
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Special Movements
Protraction
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Retraction
Special Movements
Elevation and depression:
Elevation: lifting a body part superiorly
E.g. scapulae are “elevated” when you shrug your shoulders
Depression: lifting a body part inferiorly
E.g. chewing: mandible alternates between elevation and
depression
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Special Movements
Opposition: e.g. oppostion of the thumb and
fingers
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