hand

from Wikipedia, the free encyclopedia
Leonardo da Vinci
X-ray image of a human hand

The hand ( Latin Manus , Greek χείρ cheir ) is the grasping organ of the upper extremities (arms) of the primates . In humans and most primates, it is distinguished by the opposable thumb with the opponens pollicis muscle , which enables the forceps grip ( grasping hand ). The hand is divided into the wrist ( carpus ), the metacarpus ( metacarpus ) and the fingers ( digiti manus ). In the case of the other terrestrial vertebrates, the term forefoot is mostly used, the subdivision then according to the forefoot, the pastern and the fore toe.

etymology

The common Germanic body part designation Middle High German , Old High German hant probably belongs to Gothic -hinþan “to catch, to grab” as a verbal noun formation and therefore actually means “grabber, fasserin”.

anatomy

bone

Bones of the human hand

The number of hand bones varies in vertebrates . In humans, their number is 27, so about a quarter of the bones in the human body are in the hands . The carpal ( carpus ) is formed from the eight carpal bones (scaphoid bone, moon bone, head bone, large polygonal bone, small polygonal bone, triangular bone, pea bone, hooked bone), which are articulated together. They lie in two rows, between which they form the distal wrist. The functionally more important proximal wrist is formed between the scaphoid, moonbone and triangular bone as well as the radius . In humans, the ulna is separated from the carpal bones by an articular disc . The metacarpal ( metacarpus ), which is formed from five elongated metacarpal bones, connects to the wrist .

The freely movable part of the human hand is represented by the five fingers ( digiti manus ) with their 14 finger bones (two for the thumb and three each for the other four fingers).

Muscles

Cut through the forearm. The muscles, which are largely responsible for the movement of the hand, are clearly visible

The musculature of the hand is very complex, most of the 33 muscles are in the forearm and only send its tendons into the hand. Groups of stronger muscles in the hand itself form the thenar on the thumb side and the hypothenar on the little finger side. Small muscles lie between the metacarpal bones.

annoy

The hand is supplied by three nerves : the ulnar nerve , the median nerve, and the radial nerve . The median nerve runs with the finger flexors in the area of ​​the wrist through a canal on the palm side, which is known as the carpal tunnel ( Canalis carpi ). The blood supply takes place via a double loop that forms the arteria radialis with the arteria ulnaris .

Grip and feel

The palm or palm is protected by a robust tendon plate ( palmar aponeurosis ) and thus allows a powerful grip. The skin of the hand and especially the ends of the fingers is very richly covered with various receptors ( free nerve endings , Merkel cells, etc.) and allows a high level of haptic sensitivity . In the palm of the hand, 17,000 sensory bodies (140 per cm²) absorb pressure, movement and vibration stimuli.

Variations in animals

Hand of an orangutan

After the separation of the lines of development of chimpanzees and humans, the hand has changed more than the hand of the hominini in the course of the evolution of the chimpanzee ; Compared to the chimpanzee, humans have a “more natural” hand.

Other vertebrates have developed very specialized modifications of the anatomical structure in order to adapt to their way of life. Depending on the species, some or all of the carpal bones are fused together. The number of metacarpal bones (pastern bones) and fingers (front toes) can also be reduced to varying degrees. In birds (see bird skeleton ) only three fingers are formed, in horses only one finger (the “middle finger”).

Functional range of the hand

There are two fundamentally different types of grips: the power grip and the precision grip, two names introduced by John Napier . The appropriate grip depends on the size , mass and shape of the object : power grip for heavy and larger objects, precision grip for small or fragile objects and fine instruments.

  • The power grip generally involves the entire palm of the hand including all fingers and the thumb. The thumb is in opposition to the palm. So you can hold and guide larger objects (e.g. a stone, a heavy bottle), with a force of several hundred Newtons (N) being exerted on the object.
    • The variant of the power grip with a non-opposed thumb is colloquially called monkey grip . It is particularly used by tree primates when shackling from branch to branch. He serves the people z. B. for some rescue handles or protects against injury to the thumb when using heavy hand cranks .
  • With the precision grip , objects (e.g. pencil, fine instruments) are held and guided mainly by the fingertips of the thumb and forefinger and, if necessary, the middle finger. Here is further distinguished by the fingers involved and the respective contact surfaces between the forceps grip ( fingertip of the thumb and index finger), the pliers handle (fingertips of the thumb and index finger), the three-point grip (finger tips of the thumb, index finger and ring finger) and the key bow (fingertip thumb and side surface of the front or middle phalanx of the index finger). Other variants are used depending on the shape of the object to be gripped, the respective posture and guiding task and the forces to be applied.

Furthermore, unlike all other primates , the human hand can be clenched into a fist. A shorter and more flexible thumb improves the statics of the hand and the impact is greater - an advantage in combat from an evolutionary point of view.

Other functions of the hand are the curving of the palm of the hand into a hollow shape with the involvement of the thumb and fingers, e.g. B. for scooping water (even more effective when using both hands), and supporting - be it with the ball of the hand , the fist, the flat palm with fingers or only with the front phalanges with the thumb spread apart.

As a rule, the hand on one side is preferred for more complicated sequences of movements (“ handedness ”); one speaks of right -handed and left-handed people .

Communication, counting, arithmetic, typing

Childish understanding

In addition to their central function for almost all work with bare hands or with tools , the hands are also used to transmit information, i.e. for communication purposes. This ranges from pointing and gestures to sign language .

Since the development of numbers , hands have also been used as a benchmark for counting. The frequent use of the system of ten instead of other number systems is based on the use of the ten fingers of both hands to count with the fingers. Later, however, systems were also developed with the help of which the hands were also used to express large numbers and to carry out arithmetic operations . The Anglo-Saxon Benedictine monk Beda Venerabilis (672 / 673-735) provided the first written account of finger calculation .

Even in the computer age, the hand plays a central role in the transmission of information using computer keyboards , computer mice , trackball and touch-sensitive screens .

Other aspects

The development of the hand into a complex tactile and grasping organ was an essential prerequisite for the incarnation , as anthropology was able to demonstrate, but can also be read from the size of the corresponding brain areas . In the German language , the special status of the hand pointing to terms such as hand Pedal, hand have, Be picked u. a. m.

Clinical significance

Malformations

Acquired diseases

A large number of diseases also affect the hands or parts thereof. For example:

Fractures

Common fractures are:

Others

  • The fingers of one hand are flexed and stretched about 25 million times over the course of a lifetime.
  • According to the Guinness Book of Records , the longest male hand measures 32.3 cm and the longest female hand 25.5 cm.
  • The Museum of Cultural History of the Hand in Wolnzach , Bavaria, shows around 800 exhibits. The Musée de la main in Lausanne deals with the subject of the hand from a medical and cultural-historical perspective.
  • The bent hand is the coat of arms of Brodnica (Strasburg in West Prussia).

See also

literature

  • Frank R. Wilson: The hand - a stroke of genius in evolution. Their influence on the brain, language and culture of people (= rororo non-fiction book. Rororo science 61338). Rowohlt-Taschenbuch-Verlag, Reinbek bei Hamburg 2002, ISBN 3-499-61338-7 (Original edition: The Hand. Pantheon Books, New York NY 1998, ISBN 0-679-41249-2 ).
  • Marco Wehr , Martin Weinmann (Ed.): The hand. Tool of the mind. Elsevier, Spektrum Akademischer Verlag, Munich et al. 2005, ISBN 3-8274-1517-9 .
  • Karl Groß: Galen's teleological consideration of the human hand in “de usu partium”. In: Sudhoffs Archiv 58, 1974, pp. 13-24.
  • F. Hefti: Children's orthopedics in practice . Springer 1998, ISBN 3-540-61480-X .

Web links

Wiktionary: Hand  - explanations of meanings, word origins, synonyms, translations
Wikiquote: Hand  -Quotes
Commons : Hand  - album with pictures, videos and audio files

Individual evidence

  1. ^ The dictionary of origin (=  Der Duden in twelve volumes . Volume 7 ). Reprint of the 2nd edition. Dudenverlag, Mannheim 1997 ( p. 267 ). See also Friedrich Kluge : Etymological dictionary of the German language . 7th edition. Trübner, Strasbourg 1910 ( p. 192 ).
  2. ↑ Sergio Almécija, Jeroen B. Smaers and William L. Jungers : The evolution of human and ape hand proportion. In: Nature Communications . Volume 6, Article No. 8717, 2015, doi: 10.1038 / ncomms8717
    Human hands may be more primitive than chimp's. On: sciencedaily.com from July 14, 2015
  3. ^ John Napier : The Prehensile Movements of the Human Hand. In: The Journal of Bone & Joint Surgery. Volume 38B, No. 4, 1956, pp. 902-913, doi: 10.1302 / 0301-620X.38B4.902 , full text
  4. ↑ Fine hands, fists of fury. Our hands evolved for punching, not just dexterity. On: eurekalert.org of December 19, 2012
  5. ↑ Michael H. Morgan, David R. Carrier: Protective buttressing of the human fist and the evolution of hominin hands . In: Journal of Experimental Biology . No. 216 , January 15, 2013, p. 236–244 , doi : 10.1242 / jeb.075713 (English, online [accessed on July 16, 2014] 'buttressing' German  bracing ).