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A joint is a union of two bones. Joints can either be between two
bones or a bone and a muscle. The amount of movement possible at
a particular joint depends on the type of joint that it is. The three
terms for the types of movement are: freely moveable, slightly
moveable and immovable. Freely moveable joints are also called
synovial joints. Fibrous joints are the immovable joints connected by
fibrous connective tissues. Cartilagenous joints are the slightly
moveable joints joined by cartilage and the freely moveable joints
are called synovial joints, they are not directly joined.
Synovial joints have a joint capsule, synovial membrane, a joint cavity
and articular cartilage.
- Joint capsule: surrounds the joint. It supports and stabilizes the
joint.
- Synovial membrane: is within the joint capsule. It surrounds the
joint and forms a joint cavity.
- Joint cavity: produced from synovial membrane surrounding
joint.
- Synovial fluid: a fluid secreted from the synovial membrane
that makes the surfaces of the joint smoother and slippery.
Types of Joints
There are six types of synovial joints, the ones that easily move. They
are called a hinge joint, ball-and-socket, pivot, angular (ellipsoidal or
condyloid), plane (gliding) and saddle.
Hinge joint: move along one plane, only up and down, eg elbow.
Ball-and-socket: the joint can move in any direction, eg hip and
shoulder.
Pivot: this joint allows one bone to rotate against the other, eg
radioulnar joint.
Angular: this joint permits angular movement of the bones, eg
junction between the metcarpals and phalanges,
metacarpophalangeal joint.
Plane: two flat bones joined, short gliding movement, eg intertarsal
joint
Saddle: similar to a saddle, allows joint to move in many directions,
eg joint of the thumb, carpmetacarpal joint.
Ligaments and Tendons
Ligaments connect bone to bone. They help to stabilize the joint.
They are composed mostly of long, stringy collagen fibres.
Ligaments are slightly elastic so they can be stretched to graudually
lengthen increasing flexibility.
Tendons connect muscle to bone. These are are tough and flexible
band of fibrous tissue. They attach the skeletal muscles that move
your bone. They create the motions of the bone.