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The ulna or ulnar bone (pl.: ulnae or ulnas) [3] is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm.
It joins with the scapula above at the shoulder joint (or glenohumeral joint) and with the ulna and radius below at the elbow joint. Notice : When the arm is spun so that the thumb point to the outside of the body, meaning the palm of the hand looks forward then it is said the hand is supinated.
The major exception is when the joint between these bones, the distal radioulnar joint (or DRUJ), is unstable. When the DRUJ is unstable, the ulnar styloid may require independent treatment. An excessively long styloid process of the ulna can cause painful contact with the triquetral bone in the wrist, known as ulnar styloid impaction syndrome. [1]
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
The forearm is the region of the upper limb between the elbow and the wrist. [1] The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, technically, means only the region of the upper arm, whereas the lower "arm" is called the forearm.
Wikipedia: Featured picture candidates/Image:Human arm bones diagram.svg
The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the trochlear notch of the ulna, prevents any lateral movement. Flexion in the humeroulnar joint is produced by the action of the biceps brachii and brachialis , [ 3 ] assisted by the brachioradialis , with a tiny contribution from the muscles ...
The interosseous membrane divides the forearm into anterior and posterior compartments, serves as a site of attachment for muscles of the forearm, and transfers loads placed on the forearm. The interosseous membrane is designed to shift compressive loads (as in doing a hand-stand) from the distal radius to the proximal ulna.