Joints and Bones

A point where two or more bones connect is called a joint. There are two different types of joints in the body:

• Movable joints (like ball-and-socket, hinge, gliding and pivot joints)
• Immovable joints (like the bones of the skull and pelvis) which allow little or no movement
   

Bones have two purposes. Some, like your backbone, provide the structure which enables you to stand erect instead of lying like a puddle on the floor. Other bones protect the delicate, and sometimes soft, insides of your body. Your skull, a series of fused bones, acts like a hard protective helmet for your brain. The bones, or vertebrae, of your spinal column surround your spinal cord, a complex bundle of nerves.

An adult has 206 bones in their body. Muscles pull on bones so that you can move. Along with muscles and joints, bones are responsible for you being able to move. Your muscles are attached to bones. When muscles contract, the bones to which they are attached act as levers and cause various body parts to move.

You need joints which provide flexible connections between these bones. Your body has different kinds of joints. Some, such as those in your knees, work like door hinges, enabling you to move back and forth. Those in your neck enable bones to pivot so you can turn your head. Still other joints like the shoulder enable you to move your arms 360 degrees like a shower head.

Bones are made of a mix of hard stuff that gives them strength and tons of living cells which help them grow and repair themselves. Like other cells in your body, the bone cells rely on blood to keep them alive. Blood brings them food and oxygen and takes away waste.
We have over 230 moveable and semi-moveable joints in our bodies.

We can bend, swivel, stretch, pivot, and point. Our bodies can perform more than one kind of motion because we have joints.

Hinge joints allows movement in a certain spot to take place. This joint is similar to the opening and closing of a door. Some examples of hinge joints are the elbow, knee, ankle and joints between the fingers. Hinge joints allow the body parts to bend and straighten.
 

Ball and socket joints allow twisting and turning movements. In a ball and socket joint, one of the bones has a rounded head which is the ball. The other bone has a cup-like area that is known as the socket. Some of these joints are the shoulder and the hip. The shoulder joint is the most flexible joint in the entire body. It allows movement in any direction.
 

Gliding joints allow two flat bones to slide over each other like in the bones of the foot and wrist.

Condyloid joints allows the head to nod and the fingers to bend.

Saddle joints allows enough flexibility for the thumb to touch any other finger.

Principal Joints of the body include the following:

• Acromioclavicular
• Ankle (tibia-fibula and talus)
• Atlas and axis
• Atlas and occipital
• Calcaneocuboid
• Carpometacarpal
• Elbow (humerus, radius, and ulna)
• Femur and tibia
• Hip bone and femur
• Humerus and ulna
• Intercarpal:
  • Carpal, proximal
  • Carpal, distal
  • Carpal bones (two rows with each other)
• Intermetacarpals
• Intermetatarsals
• Interphalangeal
• Knee (femur, tibia, and patella)
• Mandible (jaw) and temporal
• Metacarpophalangeal
• Metatarsophalangeal
• Pubic bones
• Radioulnar, distal
• Radioulnar, middle
• Radioulnar, proximal
• Radius-ulna and carpals (wrist)
• Ribs, heads of
• Ribs, tubercles and necks of
• Sacrococcygeal
• Sacroiliac
• Shoulder (humerus and scapula)
• Symphysis
• Sacroiliac
• Scapula and humerus
• Sternoclavicular
• Sternocostal
• Subtalar
• Talus and calcaneus
• Talus and navicular
• Tarsometatarsal
• Tibia-fibula and talus (ankle)
• Tibiofibular
• Vertebral arches
• Vertebral bodies
• Wrist (radius-ulna and carpals)

Note the double entries involving the ankle, elbow, knee and shoulder. For example, Ankle (tibia-fibula and talus) and Tibia-fibula and talus (ankle).