Chapter 6 and 7: Skeletal System and Joints

Joint (Articulation)

The point of contact between two bones, between cartilage and bone, or between teeth and bone.

Synarthrosis

An immovable joint (plural: synarthroses).

Amphiarthrosis

A slightly movable joint (plural: amphiarthroses).

Diarthrosis

A freely movable joint (plural: diarthroses); all diarthroses are structurally classified as synovial joints.

Fibrous Joints

Joints that lack a synovial cavity and have articulating bones held tightly together by dense irregular connective tissue rich in collagen fibers.

Syndesmosis

A slightly movable fibrous joint, such as the distal joint between the tibia and fibula.

Gomphosis

An immovable fibrous joint where the root of a tooth is secured into an alveolus of the mandible or maxilla.

Interosseous Membrane

A slightly movable fibrous joint formed by a sheet of connective tissue between parallel bones, such as between the radius and ulna or tibia and fibula.

Suture

A fibrous joint found exclusively between skull bones that is slightly movable in youth and later becomes immovable.

Cartilaginous Joints

Joints that lack a synovial cavity and have the articulating bones held firmly together by cartilage.

Synchondrosis

An immovable cartilaginous joint where the connecting material is hyaline cartilage, such as an epiphyseal plate.

Symphysis

A slightly movable cartilaginous joint where the connecting material is fibrocartilage, such as the pubic symphysis.

Synovial Cavity

A fluid-filled space between articulating bones that characterizes all synovial joints.

Articular Capsule

A sleeve-like structure surrounding a synovial joint composed of an outer fibrous membrane and an inner synovial membrane.

Synovial Fluid

A thin, viscous film secreted by the synovial membrane that covers surfaces within the articular capsule to lubricate the joint.

Bursae

Sac-like structures similar in construction to joint capsules that contain fluid to reduce friction in joints such as the shoulder and knee.

Tendon Sheath

A tube-like, specialized bursa that wraps around a tendon to reduce friction.

Gliding Movement

A simple joint motion where nearly flat surfaces of bones slide back-and-forth and side-to-side relative to one another.

Angular Movements

Joint motions that change the angle between articulating bones, including flexion, extension, hyperextension, abduction, adduction, and circumduction.

Rotation

A joint motion in which a bone turns around its own longitudinal axis.

Plane (Planar) Joints

Synovial joints with flat articulating surfaces that allow bones to glide back and forth or side to side; often biaxial or triaxial, such as intercarpal and intertarsal joints.

Hinge Joints

Uniaxial synovial joints where the convex surface of one bone fits into the concave surface of another to permit angular motion around one axis (e.g., elbow, knee, ankle, phalanges).

Pivot Joints

Uniaxial synovial joints where a rounded or pointed surface of one bone articulates within a ring formed by another bone and a ligament, permitting rotation (e.g., atlanto-axial and radioulnar joints).

Ball and Socket Joints

Triaxial synovial joints where a ball-like surface of one bone fits into a cuplike depression of another, allowing movement across three axes (e.g., shoulder and hip joints).

Saddle Joints

Biaxial synovial joints where the articular surface of one bone is saddle-shaped and the other sits like a rider, allowing angular motion around two axes (e.g., wrist joint and metacarpophalangeal joints of digits $2\text{--}5$).

Meniscus

Wedges of fibrocartilage located inside the knee joint that provide cushioning and stability (plural: menisci).

Arthroplasty

The surgical replacement of severely damaged natural joints with artificial prosthetic joints.

Perichondrium

A vascularized layer of dense irregular connective tissue surrounding cartilage that resists outward expansion during tissue compression.

Hyaline Cartilage

A smooth skeletal cartilage found covering ends of bones at movable joints (articular), connecting ribs to the sternum (costal), and within the larynx and nasal bridge.

Elastic Cartilage

A type of cartilage containing abundant elastic fibers, located in the external ears and the epiglottis.

Fibrocartilage

A highly compressible skeletal cartilage with high tensile strength found in the knee menisci and intervertebral discs.

Appositional Growth

Growth occurring when chondrocytes within the perichondrium secrete new matrix against the external face of existing cartilage, or when osteoblasts deposit bone matrix beneath the periosteum to increase bone thickness.

Interstitial Growth

Growth from within cartilage occurring when lacunae-bound chondrocytes divide and secrete new matrix, expanding the tissue internally.

Long Bones

Bones with greater length than width consisting of a shaft and variable ends, curved for strength (e.g., femur, tibia, fibula, humerus, ulna, radius, clavicle, and phalanges).

Short Bones

Cube-shaped bones nearly equal in length and width, such as wrist (carpal) and ankle (tarsal) bones.

Flat Bones

Thin bones providing organ protection and extensive surfaces for muscle attachment, including cranial bones, the sternum, ribs, and scapulae.

Irregular Bones

Bones with complex, complicated shapes that cannot be classified into long, short, or flat groups (e.g., vertebrae, pelvic girdle, and certain facial bones).

Sesamoid Bone

A specialized bone type embedded within tendons, exemplified by the patella.

Fontanel

The soft spot on an infant's head consisting of unossified fibrous areas between cranial bones that later fuse together.

Axial Skeleton

The central bony framework of the body consisting of the skull, vertebrae, ribs, and coccyx.

Appendicular Skeleton

The skeletal division consisting of the upper and lower limbs, as well as the shoulder and hip girdles.

Diaphysis

The tubular shaft of compact bone forming the long axis of a long bone, surrounding a central medullary cavity containing yellow bone marrow.

Epiphyses

The expanded ends of a long bone consisting of an outer compact bone shell enclosing interior spongy bone, capped with hyaline cartilage.

Epiphyseal Plate

A disc of hyaline cartilage separating the epiphysis from the diaphysis that undergoes growth to lengthen long bones (also known as the growth plate).

Tuberosity

A large, rounded, often roughened projection of bone.

Crest

A prominent, narrow ridge of bone.

Trochanter

A very large, blunt, irregularly shaped bone process found exclusively on the femur.

Condyle

A rounded articular bone projection that frequently articulates with a corresponding fossa.

Foramen

A round or oval hole or opening through a bone.

Fossa

A shallow, basin-like depression in a bone, often functioning as an articular surface.

Meatus

A canal-like passageway through a bone.

Sinus

An air-filled cavity within a bone lined with a mucous membrane.

Diploë

The internal spongy bone layer sandwiched between thin plates of compact bone within flat bone architecture.

Osteoblasts

Bone-building cells that synthesize and deposit bone matrix.

Osteoclasts

Bone-resorbing cells that dissolve and cut down bone tissue.

Intramembranous Ossification

The developmental process by which bone forms directly within fibrous connective tissue, responsible for producing the skull bones and clavicles.

Endochondral Ossification

The developmental process in which pre-existing hyaline cartilage is converted into bone, producing long bones and most other skeletal elements.

Reduction

The procedure of realigning fractured bone ends, categorized as closed (manipulated manually by hand) or open (secured surgically with pins and wires).

Parathyroid Hormone (PTH)

A hormone produced by the parathyroid gland that signals osteoclasts to resorb bone and release $$\text{Ca}^{2+}$