Hand

The hand (med / lat: .. . Manus AltGr χείρ cheir ) is the gripping member of the upper extremities (arms) of the primates. In humans and most primates, it is distinguished by the opposable thumb, which allows the pincer grip. For the other terrestrial vertebrates, the term forefoot is most commonly used.

Anatomy

Bone

Anatomically, the hand of individual bones. The number of each bone varies among vertebrates. In humans, their number is 27, in the hands thus located approximately a quarter of the bones in the human body. The wrist ( carpus ) is formed at him from the eight carpal bones ( scaphoid, lunate, capitate, Trapezium, Small trapezium, triquetrum, pisiform, hamate bone ) that are hinged together. They are in two rows, between which they form the distal wrist. The more significant functional wrist joint is formed between the scaphoid, lunate and triquetrum and the spoke. The Elle is articular separated by a discus in humans of the carpal bones. The metacarpal ( metacarpal ) adjoins the carpus, which is formed from five elongated metacarpals.

The free-moving part of the human hand, the five fingers ( digiti manus ) with a total of 14 finger bones dar. (two for the thumb and three for the other four fingers)

Muscles

The muscles of the hand is very complex, a lot of the 33 muscles located in the forearm and sends only his tendons in the hand. Groups of stronger muscles in the hand itself form the thenar on the thumb side and the hypothenar on the side of the little finger. Small muscles are located between the metacarpal bones.

Bug

The hand is supplied by three nerves: ulnar nerve, median nerve and radial nerve. The median nerve moves with the Fingerbeugern in the area of the wrist through a channel on the palm side of the carpal tunnel ( carpal tunnel ) is called. The blood supply is via a double loop which forms the radial artery with the ulnar artery.

Grip and feel

The palm and the palm is protected by a robust fascia ( aponeurosis ) and thus allows a powerful grip. The skin of the hand and particularly the finger ends is very rich with different receptors occupied ( free nerve endings, Merkel cells, and others) and allows a high degree of tactile sensitivity. In the palm of the hand take Fühlkörperchen 17,000 (140 per cm ²) pressure, motion and vibration stimuli.

Variations in animals

Other vertebrates have evolved to adapt to their way of life for some very specialized variations of the anatomy. Thus, species- specific, some or all of the carpal bones fused together. The number of the metacarpal bone ( pastern bone) and fingers ( front toe ) may be reduced to varying degrees. Thus, in birds (see Bird skeleton) is formed only three fingers in horses even just a finger (the " middle finger ").

Functions of the hand

There are two fundamentally different forms of handle types: the power grip and the precision grip. The adequate grip depends on the size, mass and shape of the object: power grip for heavy and large objects, precision grip for small or fragile items and delicate instruments.

• At the power handle accesses the entire palm of the hand, including all the fingers and thumb in general. Here is the thumb in opposition with the palm. So you can larger items (such as a stone, a heavy bottle ) hold and carry, it can be a force of several hundred Newtons ( N) exerted on the object. The variation of the power handle with non- opponiertem thumb is colloquially called monkey grip, which is especially used by living in trees in the primate hand over hand from branch to branch.
• In the precision grip posture and management of goods is effected (eg, pencil, fine instruments) mainly due to the fingertips of the thumb and index finger and the middle finger if necessary. A distinction is made between the pincer grip ( finger pads of the thumb and index finger), the pincer grasp (finger tips of the thumb and index finger), the three-point grip (finger tips of the thumb, index and ring fingers) and the key grip ( fingertip according to the involved fingers and the respective contact surfaces further of the thumb and the side surface of the front or middle finger member ). Other variants are dependent on the shape of the object to be gripped, the respective entertainment and management task and thereby forces required for use.

Furthermore, the human hand, unlike all other primates, are clenched into a fist.

Other functions of the hand are curving the palm of the hand into a hollow form involving thumb and landscaped fingers, for example, to draw water ( even more effective when using both hands), and the support - be it with the heel of the hand, the fist, the flat palm together with your fingers or with only the front phalanxes at abgespreiztem thumb.

As a rule, the hand of a page for more complex movement sequences preferred ( " handedness " ), one speaks of right and left handed users.

Use for communication, counting, calculating, Typing

In addition to its central function for almost all the work with bare hands or with tools, the hands are used for information transmission, so for purposes of communication. This ranges from showing on intentioned things or directions on gestures to complex signaling systems, such as the sign language for the deaf.

Since the development of numbers hands are used as a comparison variable for counting. The frequent use of the decimal system instead of other number systems based on the use of the ten fingers of both hands to count with your fingers. But later systems were developed, by means of which the hands have been used to express high numbers, and to perform arithmetic operations. The first written account of the fingers computing provided the Anglo-Saxon Benedictine monk Venerable Bede ( 672/673-735 ).

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

Other aspects of

The development of hand to a complex tactile and prehensile organ was essential for the Incarnation, such as anthropology was able to prove, but can also be seen from the size of the corresponding brain areas. In the German language itself shows the special status of hand by terminology such as action, handle, term, inter alia m ..

Others

• The fingers of one hand are bent and stretched about 25 million times in a lifetime.
• According to the Guinness Book of Records the longest men hand measures 32.3 cm and the longest woman's hand 25.5 cm.
• The museum cultural history of the hand in the Bavarian Wolnzach shows about 800 exhibits. The Musée de la main in Lausanne deals with the topic of hand from a medical and cultural- historical perspective.