Joints occur wherever two bones meet.

3 Structural and Functional Classifications of Joints: A. Synarthroses: These are fixed or immovable joints Fibrous: two bones are connected directly to each other by fibrous connective tissue. There are 3 kinds of fibrous joints: Syndesmosis: fibrous tissue connects two bones that work together as a unit Example: tibia and fibula; radius and ulna Suture: interlocking seams between bones Ex. Sutures of the skull Gomphosis: a peg and socket joint Ex. How teeth connect to their sockets

(b) Syndesmosis Joint held together by a ligament. Fibrous tissue can vary in length, but is longer than in sutures. Fibula Tibia Ligament Figure 8.1b

Joint held together with very short, (a) Suture Joint held together with very short, interconnecting fibers, and bone edges interlock. Found only in the skull. Suture line Dense fibrous connective tissue Figure 8.1a

(c) Gomphosis “Peg in socket” fibrous joint. Periodontal ligament holds tooth in socket. Socket of alveolar process Root of tooth Periodontal ligament Figure 8.1c

B. Amphiarthroses: These joints are partially movable. Cartilaginous: fibrocartilaginous pads separate two bones. There are 2 kinds of cartilaginous joints: a. Synchondrosis Ex. epiphyseal plates b. Symphysis Intervertebral disks; pubic symphysis

Bones united by hyaline cartilage (a) Synchondroses Bones united by hyaline cartilage Sternum (manubrium) Epiphyseal plate (temporary hyaline cartilage joint) Joint between first rib and sternum (immovable) Figure 8.2a

Bones united by fibrocartilage (b) Symphyses Bones united by fibrocartilage Body of vertebra Fibrocartilaginous intervertebral disc Hyaline cartilage Pubic symphysis Figure 8.2b

C. Diarthroses: These joints are fully movable Synovial: i. There are 6 kinds of synovial joints Plane (gliding) joint: 2 bones slide past each other Ex. Carpals and tarsals Pivot joint: one bone rotates around another Ex. Radioulnar joint Saddle joint: oval bone rests in a concave depression in another bone Ex. Thumb and triquitrium Hinge joint: allows for extension and flexion only Elbow and interphalangeal joints Condyloid (Ellipsoid) joint: allows for angular motion in two directions Knee, TMJ and neck Ball and socket: a round head fits in a depression in another bone Allows for greatest range of motion Shoulder and hip

(a) Gliding movements at the wrist Figure 8.5a

(a) Pronation (P) and supination (S) (radius rotates over ulna) Supination (radius and ulna are parallel) (a) Pronation (P) and supination (S) Figure 8.6a

Saddle

Hinge

condyloid

Ball-and-socket joint (shoulder joint) f Nonaxial Uniaxial Biaxial Multiaxial c b f Ball-and-socket joint (shoulder joint) a e d Figure 8.7f

All Synovial joints have the following parts: Articular cartilage Hyaline cartilage that cushions the ends of bones in the appendicular skeleton Only synovial joint in the axial skeleton is the temporomandibular joint (TMJ) or jaw Articular cartilage helps reduce friction when joints move. Synovial fluid Slippery fluid that occupies the space between bones in the joint cavity Lubricates the articular cartilage Stored in the bursa: membranous sacs that make and store synovial fluid Located between tendons and bones and between ligaments and bones

iii. Joint capsule iv. Joint cavity v. Ligaments Surrounds the joint Made of dense regular connective tissue Creates a sealed cavity between the bones iv. Joint cavity Found inside the joint capsule Filled with synovial fluid v. Ligaments Connect bone to bone Intrinsic ligaments are found inside the joint Ex. ACL and PCL in the knee; ligamentus capitus in hip Extrinsic ligaments are found outside the joint Ex. MCL and LCL of knee

Synovial Joints: Range of Motion 1. Nonaxial—slipping movements only 2. Uniaxial—movement in one plane 3. Biaxial—movement in two planes 4. Multiaxial—movement in or around all three planes