Joints - Better Health Channel
A joint is the part of the body where two or more bones meet to allow movement. The point at which two or more bones meet is called a joint. Joints consist of components such as ligaments, tendons, bursae and cartilage to protect the bones. Joints - Structures that connect individual bones and may allow bones to move against each other to cause movement. There are two divisions of joints.
Gliding joint — or plane joint. Smooth surfaces slip over one another, allowing limited movement, such as the wrist joints. Types of movement To achieve movement, the joint may: Slide one broad and flat surface across another — examples include the bones in the wrist or ankle.
Increase or decrease the angle between the two bones — this only occurs in the long bones of the body arms and legs: Allow a circular movement — this is how ball and socket joints work: Allow rotation without displacing the bones: Structure of a joint Joints are held together and supported by tough bands of connective tissue called ligaments.
Smooth cartilage prevents friction as the bones move against one another. In freely movable joints, the entire joint is enclosed inside a membrane filled with lubricating synovial fluid, which helps to provide extra cushioning against impact.
Muscles are attached to bones with thick, tough bands of connective tissue called tendons. Where tendons lie close to bone, tiny sacs called bursae sit between the tendon and the bone to reduce friction.
Skeletal System: Bones, Joints, Cartilage, Ligaments, Bursae
A bursa is filled with synovial fluid. When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The motor cortex on the right side of the brain controls the muscles on the left side of the body and vice versa. Sensors in the muscles and joints send messages back through peripheral nerves to tell the cerebellum and other parts of the brain where and how the arm or leg is moving and what position it's in.
This feedback results in smooth, coordinated motion. If you want to lift your arm, your brain sends a message to the muscles in your arm and you move it. When you run, the messages to the brain are more involved, because many muscles have to work in rhythm.
Muscles move body parts by contracting and then relaxing. Your muscles can pull bones, but they can't push them back to their original position. So they work in pairs of flexors and extensors.
The flexor contracts to bend a limb at a joint. Then, when you've completed the movement, the flexor relaxes and the extensor contracts to extend or straighten the limb at the same joint: For example, the biceps muscle, in the front of the upper arm, is a flexor, and the triceps, at the back of the upper arm, is an extensor.
When you bend at your elbow, the biceps contracts. Then the biceps relaxes and the triceps contracts to straighten the elbow. Joints allow our bodies to move in many ways. Some joints open and close like a hinge such as knees and elbowswhereas others allow for more complicated movement — a shoulder or hip joint, for example, allows for backward, forward, sideways, and rotating movement.
Joints are classified by their range of movement. Immovable, or fibrous, joints don't move.
The dome of the skull, for example, is made of bony plates, which must be immovable to protect the brain. Between the edges of these plates are links, or joints, of fibrous tissue. Fibrous joints also hold the teeth in the jawbone.
Bones, Muscles, and Joints (for Teens)
Partially movable, or cartilaginous pronounced: They are linked by cartilage, as in the spine. Each of the vertebrae in the spine moves in relation to the one above and below it, and together these movements give the spine its flexibility. Freely movable, or synovial pronounced: The main joints of the body — found at the hip, shoulders, elbows, knees, wrists, and ankles — are freely movable. They are filled with synovial fluid, which acts as a lubricant to help the joints move easily.
There are three kinds of freely movable joints that play a big part in voluntary movement: Hinge joints allow movement in one direction, as seen in the knees and elbows. Pivot joints allow a rotating or twisting motion, like that of the head moving from side to side.
Ball-and-socket joints allow the greatest freedom of movement. The hips and shoulders have this type of joint, in which the round end of a long bone fits into the hollow of another bone. Muscles can weaken, and joints as well as tendons, ligaments, and cartilage can be damaged by injury or disease.
The following are problems that can affect the bones, muscles, and joints in teens: Arthritis is the inflammation of a joint, and people who have it experience swelling, warmth, pain, and often have trouble moving. Although we often think of arthritis as a condition that affects only older people, arthritis also can affect children and teens.
Bones, Muscles, and Joints
Health problems that involve arthritis in kids and teens include juvenile idiopathic arthritis JIA, also know as juvenile rheumatoid arthritis, or JRAlupusLyme diseaseand septic arthritis a bacterial infection of a joint. A fracture is when a bone breaks; it may crack, snap, or shatter. After a bone fracture, new bone cells fill the gap and repair the break.
Applying a strong plaster cast, which keeps the bone in the correct position until it heals, is the usual treatment. If the fracture is complicated, metal pins and plates can be placed to better stabilize the fracture while the bone heals.
DIS-truh-fee is an inherited group of diseases that affect the muscles, causing them to weaken and break down over time. The most common form in childhood is called Duchenne muscular dystrophy, and it most often affects boys.
- What is the junction of two bones called?
OSD usually strikes active teens around the beginning of their growth spurts, the approximately 2-year period during which they grow most rapidly. In kids and teens, osteomyelitis usually affects the long bones of the arms and legs.
Joints allow both movement and flexibility. Joints are classified by how much movement they allow—function—or what they are made of—structure. Joints are usually classified structurally by the tissue that connects them. The tissue could be cartilage, fibrous tissue, synovial fluid, or some combination of the three.
Functionally, joints can be classified by the degree of movement possible, the number of bones involved, and the complexity of the joint. Most body joints allow us to move, and some only allow movement in certain ways.
Fixed or immovable joints allow no movement. A dislocated joint happens when the bones of the joint are forced out-of-place, usually while playing sports but can also happen with accidents. There are 3 major functional joints and 3 major types of structural joints. Very little movement is possible. Examples of fibrous joints are sutures, syndesmoses, and gomphoses. The growth plates of long bones are examples of this type of joint. They bones are held together in the joint by ligaments lined with synovial membranes which produce the synovial fluid.
These freely moving joints are mostly found in our arms and legs. Synovial joints also include: The articulating surfaces are covered with a layer of hyaline cartilage that cushions and protects the bones. The synovial membrane defines the boundaries of the joint space—everything outside of the synovial membrane is outside the joint space.
The synovial membrane is wrapped by layers of connective tissue that form the joint capsule.
Synovial fluid acts as a lubricant, forms a fluid seal and helps distribute the force placed on the joint. On the outside of the joint capsule are thick strap-like bands, called collateral ligaments. These ligaments direct the force that travels through the joint and keep the joint on track.
Skeletal System | Skeleton Bones, Joints, Cartilage, Ligaments, Bursae
Outside of these structures are the muscles that travel across the joint. Types of Synovial Joints Synovial Joints of the Skeletal System Based on the type of movement the joint allows and its structure, synovial joints can be put into several categories.
The way they are bound together by the ligaments may not allow movement in all directions. Examples of a gliding joint are the intertarsal and intercarpal joints of the hands and feet.