The terminal part of the upper limb, used to manipulate (motor function) or assess (sensory function) the environment. It is a highly mobile organ, capable of fine discriminative function and manipulation, both of which require a copious blood supply. It is richly endowed with sensory nerve endings, and consists of a number of bony elements (the carpels, metacarpals, and phalanges) whose size and arrangement differ between species, bound together by ligaments and supported by tendons and muscles. In humans the bony elements are the eight carpels, the five metacarpals, the three phalanges in each finger, and the two phalanges in the thumb. In primates (including humans) the thumb is set almost at right angles to the fingers, and is capable of being brought into contact with each finger in turn (opposition). Opposition is important in the precision grip (eg threading a needle). In the power grip, the thumb is used as a buttress to support the object and prevent it from slipping out of the hand (eg holding a power tool). In the hook grip only the fingers are used (eg carrying a shopping bag). The fine sensory discriminative ability of the fingers enables the blind to read braille.
The hands (med./lat.: manus, pl. Like other paired organs (eyes, ears, legs), each hand is dominantly controlled by the opposing brain hemisphere, and thus handedness, or preferred hand choice for single-handed activities such as writing with a pen, reflects a significant individual trait.
What constitutes a hand?
Although many mammals and other animals have grasping appendages similar in form to a hand, these are scientifically not considered to be so, and have other varying names, including paws. Hands must also have opposable thumbs, as described later in the text.
Humans have only two hands (except in cases of polymelia), which are attached to the arms. Some say that apes and monkeys have four hands, because the toes are long and the big toe is opposable and can somewhat be used as hands.
Uses of the hand
Grips and Grasps
There are many grips and grasps that each of us uses in our daily life: "key" grasp, "jar" grasp, "trigger grip", "hammer grip", "baseball grip", etc.
Braille
Because the fingers are so rich in nerve endings, the blind can read by running the fingers across raised dots.
Anatomy of the human hand
The human hand consists of a broad palm (metacarpus) with five digits, attached to the forearm by a joint called the wrist (carpus).
Digits
The Four Fingers
Four fingers on the hand are located at the outermost edge of the palm. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:
index finger, pointer finger, or forefinger middle finger ring finger little finger or 'pinky'The thumb
The thumb (connected to the trapezium) is located on one of the sides, parallel to the arm.
Bones
The human hand has at least 27 bones: the carpus or wrist account for 8;
Bones of the wrist
The wrist has eight bones, arranged in two rows of four.
The bones of proximal row are (from lateral to medial): scaphoid, lunate, triquetral and pisiform.
The bones of the distal row are (from lateral to medial): trapezium, trapezoid, capitate and hamate.
Bones of the palm
The palm has 5 bones (metacarpals), one to each of the 5 digits.
Digital bones
Also called phalanx bones.
Sesamoid bones
Sesamoid bones are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue.
Muscles and tendons
The movements of the human hand are accomplished by two sets of each of these tissues.
Intrinsic hand muscles
The Intrinsic muscle groups are the thenar and hypothenar muscles (thenar referring to the thumb, hypothenar to the small finger), the interosseus muscles (between the metacarpal bones, four dorsally and three volarly) and the lumbrical muscles.
The extrinsic muscles of the hand
The flexors
The fingers have two long flexors, located on the underside of the forearm.
The extensors
Located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers.
Variation
Some people have more than the usual number of fingers or toes. Alternatively, some may have large hands, and others small hands.
Articulation
Also of note is that the articulation of the human hand is more complex and delicate than that of comparable organs in any other animals.
Common uses in the English language
I know it like the back of my hand - English phrase used to say that the subject knows the matter perfectly, as if it were part of their body, or that they were born with the knowledge.
Second hand - Similar to "I know it like the back of my hand," in that it is definitely known by the subject.
A person may also describe somebody as his right hand man, which means that he relies heavily on this person;
Lending a hand is an English phrase that means helping someone.
The hand is also an archaic unit of measurement, and is currently used as the standard unit to measure the height of horses.
The hand in watches is an indicator, usually made of a thin, light piece of metal, very variable in form, which moves over a graduated dial or scale.
Gallery
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Laborer's hands, by Doris Ulmann |
Chayahuita Hands, Alto Amazonas, Loreto, Peru, 2005 |
A normal human hand has four fingers and a thumb |
So far, robotic hands have been far simpler than human hands ] |
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Bones of the human hand |
Two hands using knitting needles |
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