JOINTS

JOINTS:

DEFINITION:

  • The area where two bones are attached for the purpose of permitting body parts to move.
  • A joint is a point of articulation where two or more bones meet.
  • Joints are present at the shoulder, elbow, knee and jaw.
  • When two bones meet each other then this junction is referrred as joints.

INTRODUCTION:

  • A joint is usually formed of fibrous connective tissue and cartilage. Joints are grouped according to their type of motion; ball and socket joint, hinge joint, condyloid joint which permits all form of angular movement except axial rotation, pivot joint, gliding joint or saddle joint.
  • Joints can move in only four ways; gliding in which one bony surface glides on another, without angular or rotator movements; angular, a movement that occurs only between long bones, increasing or decreasing the angle between the bones; circumduction which occurs in joints composed of the head of bone and articular cavity, with the long bone in which a bone moves about a central axis without moving from this axis.
  • Joints are also called as athrosis or articulation.
  • Several kinds of supporting and moving parts include bones, cartilage, muscles, ligaments and tendons which help the knee to do their job.
  • Joints can separate two or more adjacent elements of the skeletal system. It is depending on the type of joints that such separated elements may or may not move on one another.
  • Bones are kept from gliding against each other by a lining called cartilage.
  • Bones are joined to bones by strong, elastic bonds of tissues called ligaments.
  • Muscles are connected to bones by tough cords of tissues called tendons.
  • Muscles pulls the tendons to move the joints.

Joint Movement:

The motions made possible by joints; such motions are spinnning, swinging, gliding, rolling and approximation.

  1. Spin movement: Spin is a movement of bone around its own long axis; it is denoted by the rotation. An example of such movements is provided by the radius; this bone can spin upon the lower end of the humerous (upper arm) in all positions of the elbow. When an individual passes the back of the hand against the mouth, the forearm is pronated or twiisted, when the palm of hand is pressed against the mouth, the forearm is supinated or untwisted. Pronation is caused by the medial (inward) rotation of the radius and supination by lateral(outward) rotation.
  2. Swing or Angular movement: This movement brings about a change in the angle of the long axis  and the moving bone and some reference line in the fixed bone. Flexion (bonding) and extension (strainghtening) of the elbow are examples of swing (to the left and right) of one boneaway from another is called abduction; the reverse adduction.
  3. Approximation: It denotes the movement caused by the pressing  or pulling, one bone directly towards another i.e. by a translation in the physical sense. The reverse of approximation is separations.
  4. Gliding and rolling movements: It occur only within synovial joints and cause moving bone to swing.

           

Classification of Joints:

Joints are either permanent or transient. The bones of  a transient joints fuse together sooner or later but always after birth. All the joints of the skull, for example, joints are transient except those of the middle ear and those between the lower jaw and the braincase. The bones of a permanent joint do not fuse together except as the result of disease or surgery. Such fusion is called arthrodesis. All permanent and some transient joint permit movement. Movement of the later may be temporary as with the roof bones of an infant’s skull during birth or long term and as with the joints of the base of the skull during postnatal development. There are two basic structural type of joint, diarthrosis, in which fluid is present and synarthrosis, in which there is no fluid. All the diathrosis or commonly called as synovial joint; they are permanent. Some of the synatrosis are transient and others are permanent.

         

There are three types of joint:

  • Fibrous joint: They are also known assynarthrodial or immovable joint. This type of joint is held together by only a ligament. Such examples are; teeth are held in their bony sockets and at both the radio=ulnar and tibio fibular joints.
  • Cartilaginous joint: They are also known as synchondroses and symphyses. These joints occur where the connection between the articulating bones is made up of cartilage Synchondroses are temporary joints which are only present in children until the end of puberty. They are permanent cartilaginous joints. For example; such joints are present between vertebrae in the spine and the epiphyseal plates in long bones.
  • Synovial joint: They are also known as diarthrosis.They are the most common joint within the human body.  These joints are moveable and have a synovial capsule i.e. have a collagenous structure which surrounds the entire joint, a synovial membrane (inner layer of the capsule), which secretes synovial fluid (a lubricating joint) and cartilage which is known as hyaline cartilage; it surrounds the ends of the articulating bones.

          

Types of synovial joint:

  • There are six types of synovial joints which are classified by the shape of the joint and the movement available:
  • Pivot joint: These joints are found at the top of spine and the knee and it allow rotation of the neck.
  • Hinge joint: It is found at the elbow and the knee. Movements available are flexion and extension.

          

Functions of Joints:

  1. Joints allow our body to move in many ways; some joints open and close like a hinge joint (such as knees or elbows) whereas others allow for more complicated movement – a shoulder or hip joint.
  2. Joints help in backward, forward, sideways and rotating movement.
  3. Joints are classified by the range of movement; immoveable or fibrous joint do not move. For example; the dome of skull made up of bony plates, which must be immoveable to protect the brain. Between the edges of these plates are links or joints which are made of fibrous tissues. Fibrous joints also hold the teeth in the jawbone.
  4. Partially moveable or cartilagenous joints move a little. They are linked by cartilagenous as in the spine. Each of the vertebrae in the spine makes in relation  to the one above and below it and together those movements give the spine a flexibility.
  5. Freely moveable or synovial joint move in any directions. The main joints of the body found at the hip, shoulders, elbows, knees, waists and ankles are freely moveable. They are filled with synovial fluid, which act as lubricant to help the joint move easily. There are three kinds of freely moveabl e joints play a big part in voluntary movemnet.
  6. Hinge joint allows the movement in one direction as seen in the knees and elbows.
  7. Pivot joint allows the rotating and twisting motion, like that of the head which can move side to side.
  8. Ball and socket joint allows the greatest freedom of movement. The hip and shoulders have the type of joint in which the round end of a long bone fits into the hollow part of another bone.

 


 

 

 

 

 

 

 

 

 

 

 

 

 

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