SKELETAL FRICTION Joints Chapter 8. Name the three major structural types of joints and compare their structure and mobility. Identify to which of these.

SKELETAL FRICTION

JointsChapter 8

• Name the three major structural types of joints and compare their structure and mobility.

• Identify to which of these three structural types any joints in the body belong.

• Classify synovial joints according to movement permitted. – • Outline the structure and functions of bursae and tendon sheaths.

Objectives

INTRODUCTION & OBJECTIVES

Joints perform two functions in the body:

1. they hold the skeletal bones together

2. they allow the rigid skeleton some flexibility so that gross movements can occur.

Classified by:Structure - fibrous, cartilaginous, synovialFunction - synarthroses, amphiarthroses, diarthroses

Functionally joints are classified as:

1. immovable joints (= synarthroses: arthrose=joint, syn=together - bone stuck together),

2. slightly movable joints (= amphiarthroses: arthrose=joint, amphi=both - in between immovable and freely movable ),

3. freely movable joints (= diarthroses: arthrose=joint, dia=apart - bone apart, can move easily).

Their structural classification is based on the nature of the material comprising them.

Structurally joints are classified as

1. fibrous joints (joints held together by fibrous connective tissue and with no joint cavity),

2. cartilaginous joints (held together by cartilage, lacking a joint cavity)

3. synovial joints (in which the joint contains a synovial cavity).

FIBROUS JOINTS (Synarthroses or Immovable) 1. Syndesmoses- ligaments

connect bones; slightly mobile Ex. radioulnar articulation

2. Sutures- interlocking junctions with fibrous tissue Ex. Skull

3. Gomphoses- roots of teeth and alveolar processes, called periodontal membrane and ligamentEx. teeth and mandible

• In fibrous joints the bones are united by dense connective tissue consisting of collagen fibers which run between the bones. There is NO JOINT CAVITY. The degree of movement permitted depends on the length of the collagen fibers, and on the shape and extent of the bone surface at the joint: most of the fibrous joints are immovable - a few are slightly movable.

CARTILAGINOUS JOINTS:

In cartilaginous joints the bones are united with each other by cartilage. Again, there is NO JOINT CAVITY.

Amphiarthroses or Slightly Movable

1. Synchondroses- use hyaline cartilage

Ex. costal cartilage; epiphyseal plate

2. Symphyses- use fibrocartilage

Ex. symphysis pubis; intervertebral disks

SYNOVIAL JOINTS: Joint cavity.

Diarthroses or Freely MovableA. Structure 1. Synovial Membrane- secretes synovial fluid

(lubrication)2. Joint cavity- contains synovial fluid aka bursa3.Articular Cartilage- hyaline; absorb compression4. Reinforcing ligaments

Synovial joints are reinforced by a number of ligaments. Ligaments are bands of dense regular connective tissue proper that connect bones to other bones. (Please do NOT mistake them for TENDONS: bands of dense regular connective tissue proper that connect muscles to bones.) The ligaments may be part of the fibrous capsule (intrinsic or capsular ligaments), or may be distinct from the fibrous capsule and found outside the capsule (extracapsular ligaments)or deep to it (intracapsular ligaments). Since intracapsular ligaments are covered with synovial membrane they do not actually lie within the joint cavity.

In some joints such as the knee, complete or partial discs (menisci) of fibrocartilage occur within the synovial cavity. They do not function in weight bearing, but act as swabs to spread synovial fluid into the joint, and help to stabilize the joint. These discs (often called `knee cartilages') are frequently torn or displaced in body contact sports .

All synovial joints are freely moveable joints.They are characterized by the PRESENCE OF A closed space or CAVITY between the bones: the joint cavity ( synovial cavity).

The majority of articulations between bones are synovial joints.

Bursae• Bursae (singular = bursa) are

closed, partially collapsed balloon containing synovial fluid and lined with synovial membrane on the inside and a fibrous membrane on the outside. They are found in the vicinity of joints where movement between two adjacent tissues might otherwise result in excessive friction. They are located between any two of bone, tendon, muscle or skin and they prevent these organs to rub against each other: like the joint cavity, with which they frequently connect, they serve to reduce friction.

SYNOVIAL JOINTS:Tendon sheath.

• Tendon sheaths are similar to bursae, but differ in shape. They look like sausage-shaped balloons that wrap around long tendons subjected to friction.

Three factors determine the strength or stability of the synovial joint, and the range of movement permitted by it. These are:

1. The shape of the articular surfaces of the bones

2. The ligaments: strong bands of dense fibrous connective tissue which bind the adjacent bones together,

3. Muscles which extend between the two bones comprising the joint.

Synovial Joint Movement Options

• Use goniometer to measure angles and range of motion of joints after injury; information aids in designing rehabilitation plans

Gliding Movements: simplest joint movement; no angular or circular mov’t; sliding

Angular Movements

1. Flexion- decrease angle; bending; folding; withdrawing a part

2. Extension & Hyperextension- increasing angle; stretching too far

3. Plantar Flexion & Dorsiflexion- foot down and back/ flex foot up

4. Abduction & Adduction- move away from median/ move towards median of body

Rotation Movements

• pivot bone around its own long axis; make a circle; medial & lateral

Special Movements

• Supination & Pronation- turn hand palm side up “soup”/ palm side down “pro BBALL”

• Inversion & Eversion- sole of foot medial/ sole of foot lateral

Special Movements

• Protraction & Retraction- part forwards/ part backwards

• Elevation and Depression- part up/ part down

• Opposition – touch thumb to other fingers; fine motor skills

Synovial joints are classified according to the shape of the articulating surfaces which, in turn, determines the range of movement permitted. They can be classified into six major categories:

1. Glding Ex. Wrists, vertebrae2. Hinge- flexion & extension

Ex. Elbow3. Pivot- rotation

1. Ex. dens of axis for skull to rotate “no”4. Saddle-Ex. thumb fits into saddle-shaped trapezium bone5. Bll & Socket- MOST RANGE OF MOTION; Ex. head of femur

and acetabulum of coxal bone

SYNOVIAL JOINTS:Plane (gliding)

• Opposite bone surfaces are flat or slightly curved.

• Only sliding motion in all directions are allowed. Since there is no bone movement around an axis, the joints are nonaxial.

SYNOVIAL JOINTS:Hinge

• Convex surface of one bone fits smoothly into concave surface of the second bone

• The movements allowed are similar to those allowed by a mechanical door hinge. Since the movements (flexion/extension) are all in one plane and around one axis, the joints are uniaxial

SYNOVIAL JOINTS:Pivot

• A rounded, pointed or conical surface of one bone is inserted into a ring made partly of another bone and partly of a ligament.

• Since the only movement allowed is the rotation of one bone around its own axis, the Joints are uniaxial

SYNOVIAL JOINTS:Saddle

• First bone's articular surface is concave in one direction and convex in the other while the second bone is just the opposite (or if you prefer, one bone is shaped like a saddle, and the other is shaped like its rider

SYNOVIAL JOINTS:Saddle

• The saddle joint is similar to the Ellipsoidal Joint but the movements are freer. The movements allowed are flexion/extension, adduction/abduction and circumduction but NO ROTATION. Since bones can move in both planes: side to side and back and forth movements the joints are biaxial.

SYNOVIAL JOINTS:Ball and Socket.

• Ball-shaped head fits into a cup-shaped depression

• These joints are the most freely moving of all synovial joints. The movements are allowed in all axes and planes: flexion/extension, adduction/abduction, circumduction and rotation. These joints are multiaxial