In human anatomy, the abductor pollicis longus (APL) is one of the extrinsic muscles of the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

. Its major function is to abduct the thumb at the wrist. Its tendon forms the anterior border of the anatomical snuffbox.

Structure

The abductor pollicis longus lies immediately below the

supinator In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm. Structure Supinator consists of two planes of fibers, between whic ...

and is sometimes united with it. It arises from the

lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...

part of the

dorsal surface Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...

of the body of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

, below the insertion of the anconeus, from the

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm * Interosseous ...

, and from the middle third of the dorsal surface of the body of the

radius In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...

.''

Gray's Anatomy ''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter, and first published in London in 1858. It has gone through multiple revised editions and the current edition, the 42nd (Octo ...

'' (1918), see infobox Passing obliquely downward and lateralward, it ends in a tendon, which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the

extensor pollicis brevis In human anatomy, the extensor pollicis brevis is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus. The extensor pollicis brevis (EPB) belongs to the ...

. The insertion is divided into a

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

, superficial part and a proximal, deep part. The superficial part is inserted with one or more tendons into the radial side of the base of the

first metacarpal bone The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophal ...

, and the deep part is variably inserted into the trapezium, the joint capsule and its ligaments, and into the belly of

abductor pollicis brevis The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. Structure The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to the ...

(APB) or

opponens pollicis The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles. It lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis. Structure The op ...

Innervation

The abductor pollicis longus muscle is innervated by the posterior interosseous nerve, which is a continuation of the deep branch of the

radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial comp ...

after it passes through the

supinator muscle In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm. Structure Supinator consists of two planes of fibers, between whi ...

. Abductor pollicis longus lies close to the radial nerve. The posterior interosseous nerve is derived from spinal segments C7 & C8.

Blood supply

Abductor pollicis longus is supplied by the

posterior interosseous artery The posterior interosseous artery (dorsal interosseous artery) is an artery of the forearm. It is a branch of the common interosseous artery, which is a branch of the ulnar artery. Structure The posterior interosseous artery passes backward be ...

Variation

An accessory abductor pollicis longus (AAPL) tendon is present in more than 80% of people, and a separate muscle belly is present in 20% of people. In one study, the accessory tendon was inserted into the trapezium (41%); proximally on the abductor pollicis brevis (22%) and opponens pollicis brevis (5%); had a double insertion on the trapezium and thenar muscles (15%); or the base of the

first metacarpal The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpopha ...

(1%).. For a dissection example se
Fig. 3
in Up to seven tendons have been reported in rare cases. Multiple APL tendons can be regarded as a functional advantage since injured tendons can be compensated by the healthy ones.

Function

The chief action of abductor pollicis longus is to abduct the thumb at the

carpometacarpal joint The carpometacarpal (CMC) joints are five joints in the wrist that articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones. The CMC joint of the thumb or the first CMC joint, also known as the trapeziometaca ...

, thereby moving the thumb anteriorly. It also assists in extending and rotating the thumb. By its continued action, it helps to abduct the wrist ( radial deviation) and flex the hand. The APL insertion on the trapezium and the APB origin on the same bone is the only connection between the thumb's intrinsic and extrinsic muscles. As the thumb is brought into action, these two muscles must coordinate to keep the trapezium stable in the carpus, which is important for the proper functioning of the thumb (i.e. precision and power grip.)

In other animals

The only

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...

s to have an APL completely separated from the

are

modern humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

and

gibbon Gibbons () are apes in the family Hylobatidae (). The family historically contained one genus, but now is split into four extant genera and 20 species. Gibbons live in subtropical and tropical rainforest from eastern Bangladesh to Northeast Indi ...

s. In gibbons, however, the APL originates proximally on the radius and ulna, whereas it originates in the middle part of these bones in crab-eating monkeys,

bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...

s, and humans. In all these primates, the muscle is inserted onto the base of the first metacarpal and sometimes onto the trapezium ( siamangs and bonobos) and thumb sesamoids (crab-eating monkeys). In

chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative t ...

s, the APL flexes the thumb rather than extends it like in modern humans. Compared to the wrists of chimpanzees, the human wrist is

derived Derive may refer to: *Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguation ...

(compared to the ''Pan-Homo'' LCA) in having considerably longer muscle moment arms for a range of hand muscles. It is possible that these differences are due to the supinated position of the trapezium in humans which, in its turn, is a result of the expansion of the trapezoid on the side of the palm. A small, lens-shaped radial

sesamoid In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for 'sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be prese ...

embedded into the APL tendon is a primitive state found in all known ''

Carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

'' genera except in the red and

giant panda The giant panda (''Ailuropoda melanoleuca''), also known as the panda bear (or simply the panda), is a bear species endemic to China. It is characterised by its bold black-and-white coat and rotund body. The name "giant panda" is sometimes u ...

s and the extinct '' Simocyon'' where it is

hypertrophied Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...

(enlarged) into a sixth digit or a so-called "false thumb", a derived trait that first appeared in ursids. The APL sesamoid is present in all non-human primates, but only in about half of

gorilla Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four ...

s, and normally absent in humans.

Gallery

File:Slide1RRRRR.JPG, Abductor pollicis longus muscle File:Slide8RRRRR.JPG, Abductor pollicis longus muscle File:Slide1SSSS.JPG, Abductor pollicis longus muscle File:Slide7SSSS.JPG, Abductor pollicis longus muscle File:Slide2TTTT.JPG, Abductor pollicis longus muscle File:Slide6TTTT.JPG, Abductor pollicis longus muscle File:Slide11TTTT.JPG, Abductor pollicis longus muscle File:Slide2TAT.JPG, Muscle of the hand.Posterior view.

Notes

References

Sources

* * * * * * * * * * {{Authority control Muscles of the upper limb