Chapter 08: Joints in Human Anatomy and Physiology

Joints

Sites where two or more bones meet.

Functions of joints

Give skeleton mobility and hold skeleton together.

Structural classifications of joints

Three types based on what material binds the joints and whether a cavity is present.

Fibrous joints

Bones joined by dense fibrous connective tissue with no joint cavity.

Sutures

Rigid, interlocking joints of skull that allow for growth during youth.

Syndesmoses

Bones connected by ligaments, with movement varying based on fiber length.

Gomphoses

Peg-in-socket joints, specifically the teeth in alveolar sockets.

Cartilaginous joints

Bones united by cartilage, similar to fibrous joints, with no joint cavity.

Synchondroses

Bar or plate of hyaline cartilage that unites bones, almost all are synarthrotic.

Symphyses

Fibrocartilage unites bone in symphysis joint, strong and slightly movable.

Synovial joints

Bones separated by fluid-filled joint cavity, all are diarthrotic.

Articular cartilage

Consists of hyaline cartilage covering ends of bones, prevents crushing of bone ends.

Joint (synovial) cavity

Small, fluid-filled potential space that is unique to synovial joints.

Articular (joint) capsule

Two layers thick: external fibrous layer and inner synovial membrane.

Synovial fluid

Viscous, slippery filtrate of plasma and hyaluronic acid that lubricates and nourishes articular cartilage.

Bursae

Fluid-filled sacs that reduce friction between moving parts in joints.

Tendon sheaths

Elongated bursa that wraps around a tendon to reduce friction.

Diarthroses

Freely movable joints.

Synarthroses

Immovable joints.

Amphiarthroses

Slightly movable joints.

Sutures ossify

In middle age, sutures fuse and become immovable joints referred to as synostoses.

Interosseous membrane

Connects radius and ulna, allowing a larger amount of movement.

Temporary epiphyseal plate joints

Become synostoses after plate closure.

Cartilage of 1st rib

Joins with manubrium of sternum.

Intervertebral joints

Examples of symphyses that are slightly movable.

Pubic symphysis

Example of a symphysis joint that is slightly movable.

Hyaline cartilage

Present as articular cartilage on bony surfaces in symphyses.

Phagocytic cells

Cells contained in synovial fluid that remove microbes and debris.

Capsular

Thickened part of fibrous layer

Extracapsular

Outside the capsule

Intracapsular

Deep to capsule; covered by synovial membrane

Nerves

Detect pain; monitor joint position and stretch

Capillary beds

Supply filtrate for synovial fluid

Fatty pads

For cushioning between fibrous layer of capsule and synovial membrane or bone

Articular discs (menisci)

Fibrocartilage separates articular surfaces to improve 'fit' of bone ends, stabilize joint, and reduce wear and tear

Bursae

Reduce friction where ligaments, muscles, skin, tendons, or bones rub together

Tendon sheaths

Elongated bursae wrapped completely around tendons subjected to friction

Stability of joints

Three factors determine stability to prevent dislocations: shape of articular surface, ligament number and location, and muscle tone

Shape of articular surface

Minor role; shallow surfaces less stable than ball-and-socket

Ligament number and location

Limited role; the more ligaments, the stronger the joint

Muscle tone

Keeps tendons taut as they cross joints; most important in reinforcing shoulder and knee joints and arches of the foot

Origin

Attachment to immovable bone

Insertion

Attachment to movable bone

Nonaxial movement

Slipping movements only

Uniaxial movement

Movement in one plane

Biaxial movement

Movement in two planes

Multiaxial movement

Movement in or around all three planes

Gliding movements

One flat bone surface glides or slips over another similar surface

Examples of gliding movements

Intercarpal joints, Intertarsal joints, Between articular processes of vertebrae

Angular movements

Increase or decrease angle between two bones

Flexion

Decreases the angle of the joint

Extension

Increases the angle of the joint

Hyperextension

Movement beyond the anatomical position

Three general types of movements

Gliding, Angular movements, Rotation

Abduction

Movement along frontal plane, away from the midline.

Adduction

Movement along frontal plane, toward the midline.

Circumduction

Involves flexion, abduction, extension, and adduction of limb; limb describes cone in space.

Rotation

Turning of bone around its own long axis, toward midline or away from it.

Medial Rotation

Rotation toward midline.

Lateral Rotation

Rotation away from midline.

Supination

Palms face anteriorly; radius and ulna are parallel.

Pronation

Palms face posteriorly; radius rotates over ulna.

Dorsiflexion

Bending foot toward shin.

Plantar Flexion

Pointing toes.

Inversion

Sole of foot faces medially.

Eversion

Sole of foot faces laterally.

Protraction

Mandible juts out.

Retraction

Mandible is pulled toward neck.

Elevation

Lifting body part superiorly; example: shrugging shoulders.

Depression

Lowering body part; example: opening jaw.

Opposition

Movement of thumb; example: touching thumb to tips of other fingers on same hand or any grasping movement.

Types of Synovial Joints

There are six different types of synovial joints based on shape of articular surface and movement joint is capable of.

Plane Joint

One of the six types of synovial joints.

Hinge Joint

One of the six types of synovial joints.

Pivot Joint

One of the six types of synovial joints.

Condylar Joint

One of the six types of synovial joints.

Saddle Joint

One of the six types of synovial joints.

Ball-and-Socket Joint

One of the six types of synovial joints.