A finger is a prominent digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (pentadactyly),[1][2] and short digits (i.e. significantly shorter than the metacarpal/metatarsals) are typically referred to as toes, while those that are notably elongated are called fingers. In humans, the fingers are flexibly articulated and opposable, serving as an important organ of tactile sensation and fine movements, which are crucial to the dexterity of the hands and the ability to grasp and manipulate objects.

As terrestrial vertebrates were evolved from lobe-finned fish, their forelimbs are phylogenetically equivalent to the pectoral fins of fish. Within the taxa of the terrestrial vertebrates, the basic pentadactyl plan, and thus also the metacarpals and phalanges, undergo many variations.[3]Morphologically the different fingers of terrestrial vertebrates are homolog. The wings of birds and those of bats are not homologous, they are analogue flight organs. However, the phalanges within them are homologous.[4]


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Chimpanzees have lower limbs that are specialized for manipulation, and (arguably) have fingers (instead of toes) on their lower limbs as well. In the case of primates in general, the digits of the hand are overwhelmingly referred to as "fingers".[5][6] Primate fingers have both fingernails and fingerprints.[7]

Research has been carried out on the embryonic development of domestic chickens showing that an interdigital webbing forms between the tissues that become the toes, which subsequently regresses by apoptosis. If apoptosis fails to occur, the interdigital skin remains intact. Many animals have developed webbed feet or skin between the fingers from this like the Wallace's flying frog.[8][9][10]

The palm has five bones known as metacarpal bones, one to each of the five digits. Human hands contain fourteen digital bones, also called phalanges, or phalanx bones: two in the thumb (the thumb has no middle phalanx) and three in each of the four fingers. These are the distal phalanx, carrying the nail, the middle phalanx, and the proximal phalanx.Joints are formed wherever two or more of these bones meet. Each of the fingers has three joints:

Each finger may flex and extend, abduct and adduct, and so also circumduct. Flexion is by far the strongest movement. In humans, there are two large muscles that produce flexion of each finger, and additional muscles that augment the movement. The muscle bulks that move each finger may be partly blended, and the tendons may be attached to each other by a net of fibrous tissue, preventing completely free movement. Although each finger seems to move independently, moving one finger also moves the other fingers slightly which is called finger interdependence or finger enslaving.[14][15][16]

Muscles of the fingers can be subdivided into extrinsic and intrinsic muscles.The extrinsic muscles are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.

The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.

The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor, used for instance for pointing. The extensors are situated within six separate compartments. The first compartment contains abductor pollicis longus and extensor pollicis brevis. The second compartment contains extensors carpi radialis longus and brevis. The third compartment contains extensor pollicis longus. The extensor digitorum indicis and extensor digitorum communis are within the fourth compartment. Extensor digiti minimi is in the fifth, and extensor carpi ulnaris is in the sixth.

Aside from the genitals, the fingertips possess the highest concentration of touch receptors and thermoreceptors among all areas of the human skin,[citation needed] making them extremely sensitive to temperature, pressure, vibration, texture and moisture. Recent studies[when?] suggest fingers can feel nano-scale wrinkles on a seemingly smooth surface, a level of sensitivity not previously recorded.[17] This makes the fingers commonly used sensory probes to ascertain properties of objects encountered in the world, making them prone to injury.

Although a common phenomenon, the underlying functions and mechanism of fingertip wrinkling following immersion in water are relatively unexplored. Originally it was assumed[by whom?] that the wrinkles were simply the result of the skin swelling in water,[citation needed] but it is now understood that the furrows are caused by the blood vessels constricting due to signalling by the sympathetic nervous system in response to water exposure.[19][20] One hypothesis for why this occurs, the "rain tread" hypothesis, posits that the wrinkles may help the fingers grip things when wet, possibly being an adaption from a time when humans dealt with rain and dew in forested primate habitats.[19] A 2013 study supporting this hypothesis found that the wrinkled fingertips provided better handling of wet objects but gave no advantage for handling dry objects.[21] However, a 2014 study attempting to reproduce these results was unable to demonstrate any improvement of handling wet objects with wrinkled fingertips.[20]

The somatosensory cortex representation of the hand is a dynamic reflection of the fingers on the external hand: in syndactyly people have a clubhand of webbed, shortened fingers. However, not only are the fingers of their hands fused, but the cortical maps of their individual fingers also form a club hand. The fingers can be surgically divided to make a more useful hand. Surgeons did this at the Institute of Reconstructive Plastic Surgery in New York to a 32-year-old man with the initials O. G.. They touched O. G.'s fingers before and after surgery while using MRI brain scans. Before the surgery, the fingers mapped onto his brain were fused close together; afterward, the maps of his individual fingers did indeed separate and take the layout corresponding to a normal hand.[27]

A rare anatomical variation affects 1 in 500 humans, in which the individual has more than the usual number of digits; this is known as polydactyly. A human may also be born without one or more fingers or underdevelopment of some fingers such as symbrachydactyly. Extra fingers can be functional. One individual with seven fingers not only used them but claimed that they "gave him some advantages in playing the piano".[28]

The fingers are commonly affected by diseases such as rheumatoid arthritis and gout. Diabetics often use the fingers to obtain blood samples for regular blood sugar testing. Raynaud's phenomenon and Paroxysmal hand hematoma are neurovascular disorders that affect the fingers.

Research has linked the ratio of lengths between the index and ring fingers to higher levels of testosterone, and to various physical and behavioral traits such as penis length[29] and risk for development of alcohol dependence[30] or video game addiction.[31]

The name pinkie derives from Dutch pinkje, of uncertain origin. In English only the digits on the hand are known as fingers. However, in some languages the translated version of fingers can mean either the digits on the hand or feet. In English a digit on a foot has the distinct name of toe.

An account is given of the discovery of the classical Cys(2)His(2) zinc finger, arising from the interpretation of biochemical studies on the interaction of the Xenopus protein transcription factor IIIA with 5S RNA, and of structural studies on its structure and its interaction with DNA. The finger is a self-contained domain stabilized by a zinc ion ligated to a pair of cysteines and a pair of histidines, and by an inner hydrophobic core. This discovery showed not only a new protein fold but also a novel principle of DNA recognition. Whereas other DNA binding proteins generally make use of the two-fold symmetry of the double helix, zinc fingers can be linked linearly in tandem to recognize nucleic acid sequences of varying lengths. This modular design offers a large number of combinatorial possibilities for the specific recognition of DNA (or RNA). It is therefore not surprising that the zinc finger is found widespread in nature, including 3% of the genes of the human genome. The zinc finger design is ideally suited for engineering proteins to target specific genes. In the first example of their application in 1994, a three-finger protein was constructed to block the expression of an oncogene transformed into a mouse cell line. In addition, a reporter gene was activated by targeting an inserted zinc finger promoter. Thus, by fusing zinc finger peptides to repression or activation domains, genes can be selectively switched off or on. It was also suggested that by combining zinc fingers with other effector domains, e.g., from nucleases or integrases, to form chimeric proteins, genomes could be manipulated or modified. Several applications of such engineered zinc finger proteins are described here, including some of therapeutic importance. ff782bc1db

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