Nice Bones in a Joint Like This Quiz

Answer: ball-and-socket joint

The ball-and-socket joint (sometimes called a "universal joint") allows us to swing our arms in circles and move them in all directions. The hip is also a ball-and-socket joint, although it does not move as freely as the shoulder. In a ball-and-socket joint, the rounded end of one bone fits smoothly into a matching indentation in another bone.

Answer: hinge joint

Each of the hinge joints in the human body is more complex than a door hinge, but the same principle applies. With the help of muscles, tendons, and ligaments, hinge joints act as simple machines, like levers. Unlike a ball-and-socket joint, which can move in circles and in many directions, a hinge joint only moves back and forth in one direction. Ellipsoidal joints (also called condyloid joints) can move in two planes and are found in the wrists and ankles.

There are hinge joints in the phalanges (fingers and toes), but the word "phalanges" refers to the finger and toe bones, not a type of joint.

Answer: saddle joint

The human thumb is opposable and prehensile (grasping), and is capable of flexion (bending inwards); extension (bending or stretching outwards); abduction (moving away from the palm); adduction (moving towards the palm, touching the side); opposition (rotation to face the palm and touch the other fingers); and circumduction (complete rotation). Because these movements make so many human activities possible, the importance of the small saddle joint cannot be overemphasized.

Answer: skull

A small bit of movement at the sutures of the adult skull (cranium) allows some "give" to better protect the separate flat bones of the head and keep them from shattering. At birth, these bones are not yet fused, a fact that can be confirmed if you gently touch the fontanelle (soft spot) on the top of an infant's head.

This greater flexibility allows the head of a baby to "mold" as it goes safely through the relatively narrow birth canal. Babies are born with around 300 bones (sources variously estimate as few as 270 and as many as 350) and a great deal of flexible cartilage, but by adulthood bones have knit together and hardened, and adult humans have only 206 bones.

Answer: hyoid

Seven pairs of strong muscles that act like pulleys moving in different directions--along with ligaments, tendons, and thyroid cartilage--keep the hyoid bone in place and connect it to the temporal bone (one of the sections of the skull), the mandible (the jawbone), and the larynx (voice box); muscles attached to the hyoid bone even reach down to the sternum (breastbone) and scapula (shoulder blade). So, while it is not directly attached to another bone at a joint, the hyoid bone functions as part of a complex of structures within the musculoskeletal system.

Answer: ligaments

Ligaments limit joint movement and hold the bones together; they are strong fibers of connective tissue that attach bone to bone and form capsules around synovial joints. Tendons, also made of strong connective fibers, attach bones to muscles and act like pulleys, using the bone as support to move the muscle. A third kind of connective tissue, the fasciae, connects muscle to muscle. The direction and degree to which tendons and muscles function is partially determined by ligaments, which stabilize joints and work in tension with the other structures.

Answer: ball-and-socket joint / hip

The hip joint (acetabulofemoral joint) is a ball-and-socket joint, with the ball-like protrusion at the top of the femur (long bone of the upper leg) fitting neatly into the cup-like socket of the acetabulum (part of the pelvis). The hip joint supports the weight of the body and helps us keep our balance and posture, whether we are walking, running, dancing, or standing still.

Answer: hyaline cartilage

Hyaline cartilage, also called articular cartilage, covers the surface at the ends of long bones where they articulate: that is, where they form a joint that allows one bone to move in relation to another bone. The expanded end of a long bone is called its epiphysis. Cartilage is a type of connective tissue, while epithelial tissue is a different kind of tissue that covers the surfaces of the body, inside and out (skin, the lining of the gastrointestinal system, etc.). (The prefix "epi" in the words "epiphysis" and "epithelial" simply means "on, upon, at, by, near, over, on top of, toward, against, among"--the roots of the two words are unrelated.) Adipose tissue is a type of loose connective tissue that stores fat. Enamel covers the teeth, which are not bones, although they are considered part of the skeletal system.

Answer: synovial fluid

Synovial fluid functions with cartilage to cushion joints that move, which are appropriately termed synovial joints. Types of synovial joints include hinge joints, ball-and-socket joints, saddle joints, pivot joints, and others. Osteoarthritis occurs when synovial fluid loses its consistency with age, contributing to the breakdown of cartilage, which in turn causes bones to rub against each other and become damaged.

Some joints, such as the hip and the knee, can now be surgically replaced when they become damaged through injury or the wear and tear of age.

Answer: head

The atlas and axis are two tiny bones at the top of the spinal column, where it meets the bones of the skull. For the head to turn from side to side and to stretch up and down, a special sort of joint is needed. The atlas is the first cervical vertebra (C1) and is symbolically named for the Greek Titan Atlas, who held the globe of the earth on his shoulders.

The axis is the second cervical vertebra (C2), and its name comes from the Greek word for an axle that turns a wheel. The axis forms the pivot on which the ring-like atlas rotates. Amazingly intricate and elegant!