ARM

Microprocessor developed by Acorn in 1985 for use in the Archimedes microcomputer. In 1990 the company Advanced RISC Machines was formed to develop the ARM microprocessor. The ARM family of microprocessors are used in a variety of personal digital assistants, mobile phones, and other consumer electronic devices.

arm

The movements of the arm depend on two muscles, the biceps and the triceps. To lift the arm, the biceps shortens and the triceps lengthens. To lower the arm, the opposite occurs: the biceps lengthens and the triceps shortens.

Fore or upper limb in humans from the shoulder to the wrist. The humerus, or bone of the upper arm, fits at the top into the scapula, or shoulder blade. At the lower end it articulates with the radius and ulna, the bones of the forearm. These are articulated with each other and with the wrist bones.

The deltoid is the large muscle that forms the shoulder cap and serves to raise the arm from the side; it runs from the shoulder blade to the middle of the humerus. The chief muscles engaged in lowering the arm again are the latismus dorsi, which runs forwards and upwards from the back and side of the chest wall to be attached to the front of the neck of the humerus; the coraco-brachialis, attached to the middle of the front of the humerus; and the pectoralis major, which forms the front fold of the armpit.

The arm is flexed by the biceps, running from shoulder to elbow joint in front, and is straightened by the triceps, running from shoulder to elbow at the back. The muscles of the forearm consist of the flexors and extensors of the wrist and fingers.

The chief arteries are the axillary, passing through the armpit, and becoming the brachial as it traverses the upper arm, and the radial and ulnar arteries, which are the branches of the brachial running down the lower arm.

Fracture of the humerus Fracture of the upper end of the humerus may result from direct or indirect violence. The neck or narrow part below the head is the most frequent seat of the fracture, which may result from a fall upon the shoulder, or indirectly from a fall on the outstretched hand or elbow. The bone is usually broken transversely with outward displacement of the upper fragment. Fracture of the shaft of the humerus is usually caused by a blow on the arm. The broken ends as a rule overlap considerably owing to the pull of the muscle spasm. Fractures of the lower end of the humerus are commonly caused by falls on the outstretched hand and may involve the elbow joint.

A rare but unpleasant complication of fractures in the region of the elbow is known as Volkmann's ischaemic contracture. In this condition the blood supply to the forearm is considerably reduced with the result that the muscles waste, becoming fibrosed and contracted, causing a flexion deformity. This is thought to be due to spasmodic contraction of the blood vessels caused by the fracture.

Fracture of the radius and ulna Of the bones of the forearm, the radius is more liable to fracture, but both may be broken by a direct blow or fall. Colles's fracture is a fracture of the end of the radius, about 2–3 cm/0.8–1.2 in above the articular surface. It is usually caused by a fall on the open palm when the elbow is slightly flexed, and produces a characteristic backward displacement of the lower fragment and the hand. When fixing the arm in splints, the fingers should be left unconfined, so that after the first day the patient may move them freely; this is necessary in order to prevent adhesion of the tendons to their sheaths.