Hand

From ArticleWorld

The hand is a multi-articulated portion of the distal end of the primate upper extremities. It is the part of the body that has the ability to exhibit many small movements, such as those required for typing, writing, picking up small objects and grasping small objects. To be called a “hand” instead of a “paw” the appendage must have an opposable thumb.

Anatomy

The hand is made of multiple bones. The five metacarpal bones together attach to the bones of the wrist and, along with interosseous muscles, fat and connective tissue, form the two flat surfaces of the hand. The palmar surface is also called the palm of the hand. The dorsal surface is known as the back of the hand.

A phalanx is any bone that extends out to support the fingers or the thumb. Each hand has 14 phalanges. Each finger has a proximal, middle and a distal phalanx. The thumb has only a proximal and a distal phalanx. The term, opposable, means that the thumb can be brought across the palm of the hand to touch any of the fingers.

Function

The muscles of the hand give it the function it needs. There are extrinsic muscles, that move the hand but originate higher in the forearm, and intrinsic muscles, that are solely in the hand itself. The extrinsic muscles are divided into flexors and extensors. The flexors are on the underside of the hand. The extensor muscles are on the dorsal side of the forearm and insert into the phalanges, allowing the hand to actively flatten.

The thumb has a flexor that originates outside the hand and a short flexor within the hand itself. The short flexor is in a bundle of muscles called the thenar muscles. The thenar muscles form the fleshy part of the palm at the base of the thumb. The opponens pollicis muscle and the adductor pollicis muscles are also a part of the thenar muscles that allow the thumb to oppose and draw the thumb next to the index finger, respectively.

The intrinsic muscles of the hand include the thenar muscles and the abductor digiti minimi muscle that allows just the fifth finger (pinkie finger) to draw away from the rest of the fingers. Between the metacarpals are several interosseous muscles that fill in the gaps between the bones.

Conditions

There are several common hand-related injuries. During sports, primarily, one of the phalanges can become dislocated. Punching something often causes an injury to the fifth metacarpal, called a Boxer’s fracture. Because the hand is used for so many things, various kinds of tendonitis can affect one or more of the fingers or the hand itself. Pain often radiates up the forearm muscle associated with the inflamed tendon.