JOINTS: Classification, How Joints Move, Synovial Joints, Name of Joints

Structural features of a synovial joint: - ligament

#1 - Attaches bone to bone

Functional classification of joints

1. *Synarthrosis* (fibrous): immovable joints (e.g. sutures of skull) 2. *Amphiarthrosis* (cartilaginous): slightly movable joints (e.g. pubic symphysis; intervertebral discs) 3. *Diarthroses* (synovial): freely movable (e.g. all synovial joints)

Types of Synovial Joints

1. Plane (gliding) 2. Hinge 3. Pivot 4. Saddle 5. Condyloid (ellipsoid) 6. Ball and socket

Joint functions?

They hold the skeletal bones together and allow the skeleton some flexibility so gross movements can occur

Plane (gliding) joints - examples

- Have two flat faces of bone that slide over one another. They allow for a *small* amount of movement in *all directions*. - The joints are *nonaxial* since there is no movement occurring around an axis. - *Example*: carpals and tarsals

Ellipsoidal (condyloid) joints

- Joints have an oval-shaped surface fitting into an oval-shaped cavity - The movements allowed are flexion/extentsion, adbuction/adduction, and circumduction BUT *no rotation* can occur. - Joints are *biaxial* since bones can move around two axes - *Example*: Joints between the metacarpals and phalanges (knuckles)

Saddle joints

- The first bone's articulating surface is concave in one direction while the second bone is concave in the opposite direction (i.e. one bone is the rider, the other bone is the saddle) - Joints are *biaxial* since bones can move around two axes: flexion/extentsion, adbuction/adduction, and circumduction can occur BUT *no rotation*. Same as condyloid but freer. - *Example*: Thumb and sternoclavicular joints

Structural features of a synovial joint: - synovial (joint) cavity

#2 - Space created by the articular capsule and filled with synovial fluid

Structural features of a synovial joint: - articulating cartilage

#3 - Very thin layer of hyaline cartilage covering the articulating surface of two adjoining bones

Structural features of a synovial joint: - fibrous layer

#4 - External layer of the articular capsule surrounds joint cavity. Attaches to the surface of the bone and is continuous with the *periosteum*

Structural features of a synovial joint: - synovial membrane

#5 - Internal layer of loose CT that covers all internal joint surfaces that are not hyaline cartilage. It secretes *synovial fluid*

Structural features of a synovial joint: - articular capsule

#6 - The double-layer capsule creating the *synovial cavity*. It's composed of the *synovial membrane layer* and *fibrous layer*

What are joints?

*Joints* are the articulation points between two or more bones. Every bone (except for the *hyoid*) connects with at least one other bone.

Menisci vs Articular Discs

- *Meniscus* often refers to the cartilage of the knee, either the lateral or medial menisci. - In contrast, *articular discs* are present in several joints other than the knee (e.g. acromioclavicular joint, sternoclavicular joint, radio-carpal joint, temporomandibular joint)

Function of ligaments

- CT that connects bone to bone. They are responsible for holding joints together and prevent bones moving out of position during the stress of physical activity

Function of Tendons and how they attach muscle to bone?

- CT that connects muscles to bones, allowing muscles to move the skeleton. Tendons are not very elastic. - Tendons can attach *muscle to bone* by: 1. *Aponeurosis*: flat broad tendon sheeth (scalp, abdomen, lumbar, palmar / plantar, extensor hoods) 2. *Direct muscle attachment* to bone: microscopic tendons attach muscle to bone 3. *Indirect muscle attachment* to bone: gross tendons attach muscle to bone

What are menisci and what is their function?

- Complete or partial discs of *fibrocartilage* that occur *within the synovial cavity* of certain joints such as the knee - They act to disperse weight, reduce friction during movement, spread synovial fluid into joint, and stabilize joint

Structural features of a synovial joint: - synovial fluid

- Fluid secreted by the synovial membrane (#5) that lines the cavity. Fluid is highly viscous and slippery to reduce friction

What is the function of reinforcing ligaments? Types?

- Reinforce and strengthen synovial joints. They can be capsular and contribute to the articulating capsule - *Extracapsular ligaments*: reinforcing ligament that is located *outside of the articular capsule*. Made up of bands of dense regular connective tissue that provides strength to joint - *Intracapsular ligament*: internal to the synovial joint (e.g. anterior cruciate ligament)

Tendon sheaths

- Similar to bursae but differ in shape - They look like sausage-shaped balloons that wrap around long tendons subjected to friction

Hinge joints

- The convex surface of one bone fits onto the concave surface of another bone. The movement allowed is similar to the opening and closing of a door. - These joints are *uniaxial* since movement (*flexion/extension*) takes place along one axis - *Example*: knee and elbow joint

Ball and socket joints

- The rounded end of one bone fits inside the cup-shaped depression on another bone. These are the most freely moving of all synovial joints - They are *multiaxial* since movements are allowed in all axes of rotation and planes: flexion/extension, abduction/adduction, medial/lateral rotation, circumduction - *Example*: shoulders and hips

Pivot joints

- These joints have a "ring" of bone that fits over a bone protrusion, around which it can rotate. - Joints are *uniaxial* since *rotation* along the vertical axis is the only movement allowed - *Example*: Atlas and axis joint in neck

What are bursae and where are they found?

- They are closed, partially collapsed *balloon-like* structures containing synovial fluid and lined with an inner synovial membrane and an outer fibrous membrane - They are found in the vicinity of joints where movement between 2 adjacent tissues might otherwise result in excessive friction

Structural classification of joints

1. *Fibrous* (synarthrosis): bones joined by fibrous connective tissue. Examples: sutures, synemoses (2 bones connected by fibrous membranes), gomphoses (teeth fitting into fibrous pockets of the skull) 2. *Cartilaginous* (amphiarthrosis): bones joined by cartilage, or by cartilage and fibrous tissue. 3. *Synovial* (diarthrosis): bones joined by a joint cavity fill with a small amount of synovial fluid and surrounded by a capsule; the bony articular surfaces are covered with hyaline cartilage

How joints move: 1. nonaxial 2. uniaxial 3. biaxial 4. multiaxial

1. *nonaxial*: joint allows small amount of movement in all directions (e.g. carpal/tarsal joints) 2. *uniaxial*: movement that takes place around a single axis (e.g. elbow flexion-extension) 3. *biaxial*: joint allows for motion within two planes (e.g. between the metacarpals and phalanges) 4. *multiaxial*: joint allows for movement in all axes of rotation and planes - allows flexion-extension; abduction-adduction, circumduction; and medial-lateral rotations. (e.g. shoulder and hip joints)

The 3 types of connective tissue important for the functioning of joints

1. Tendons 2. Ligaments 3. Cartilage

Name body joints

See Diagrams

What are synovial joints characterized by?

Synovial joints are characterized by the presence of a cavity (closed space) between the bones: the *synovial cavity*