Flexor pollicis longus muscle
Encyclopedia
The flexor pollicis longus (FPL, Latin flexor, bender; pollicis, thumb; longus, long) is a muscle in the forearm
and hand
that flexes the thumb. It lies in the same plane as the flexor digitorum profundus.
This muscle is unique to humans, being "either rudimentary or absent" in other primates.
, extending from immediately below the radial tuberosity
and oblique line to within a short distance of the pronator quadratus
muscle.
It arises also from the adjacent part of the interosseous membrane of the forearm
, and generally by a fleshy slip from the medial border of the coronoid process
of the ulna
. In 40 per cent of cases, it is also inserted from the medial epicondyle
of the humerus
, and in those cases a tendinous
connection with the humeral head of the flexor digitorum superficialis
is present.
The fibers end in a flattened tendon, which passes beneath the flexor retinaculum of the hand
through the carpal tunnel
. It is then lodged between the lateral head of the flexor pollicis brevis and the oblique part of the adductor pollicis, and, entering an osseo
aponeurotic
canal similar to those for the flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb.
(a branch of the median nerve
) and the anterior interosseous artery and vein pass downward on the front of the interosseous membrane between the flexor pollicis longus and flexor digitorum profundus.
Injuries to tendons are particularly difficult to recover from due to the limited blood supply they receive.
(FDP). While the FPL is not a separate muscle belly in extant great apes
, a distinct tendon from the FDP belly might be present. In some individuals this tendon tend to act more like a ligament which restricts extension of the interphalangeal joint of the thumb. In orangutan
s there is a tendon similar in insertion and function to the FPL in humans, but which has an intrinsic origin on the oblique head of the adductor pollicis
.
Lesser apes (i.e. gibbons) and Old World monkey
s (e.g. baboons) share an extrinsic FPL muscle tendon with humans. In most lesser apes the FPL belly is separate from the FDP belly, but in baboons the FPL tendon bifurcates from the FDP tendon at the wrist within the carpal tunnel
and, because of the lack of differentiation in both the FDP and FPL musculature, it is unlikely that baboons can control individual digits independently.
Forearm
-See also:*Forearm flexors*Forearm muscles...
and hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
that flexes the thumb. It lies in the same plane as the flexor digitorum profundus.
This muscle is unique to humans, being "either rudimentary or absent" in other primates.
Origin and insertion
It arises from the grooved anterior (side of palm) surface of the body of the radiusRadius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
, extending from immediately below the radial tuberosity
Radial tuberosity
Beneath the neck of the radius, on the medial side, is an eminence, the radial tuberosity; its surface is divided into:* a posterior, rough portion, for the insertion of the tendon of the biceps brachii....
and oblique line to within a short distance of the pronator quadratus
Pronator quadratus
Pronator quadratus is a square shaped muscle on the distal forearm that acts to pronate the hand.As it is on the anterior side of the arm, it is innervated by a branch of the median nerve, the anterior interosseous nerve...
muscle.
It arises also from the adjacent part of the interosseous membrane of the forearm
Interosseous membrane of the forearm
The interosseous membrane of the forearm is a fibrous sheet that connects the radius and the ulna...
, and generally by a fleshy slip from the medial border of the coronoid process
Coronoid process of the ulna
The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna.Its base is continuous with the body of the bone, and of considerable strength....
of the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
. In 40 per cent of cases, it is also inserted from the medial epicondyle
Medial epicondyle of the humerus
The medial epicondyle of the humerus, larger and more prominent than the lateral epicondyle, is directed a little backward. In birds, where the arm is somewhat rotated compared to other tetrapods, it is called ventral epicondyle of the humerus....
of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, and in those cases a tendinous
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
connection with the humeral head of the flexor digitorum superficialis
Flexor digitorum superficialis muscle
Flexor digitorum superficialis is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints....
is present.
The fibers end in a flattened tendon, which passes beneath the flexor retinaculum of the hand
Flexor retinaculum of the hand
The flexor retinaculum is a strong, fibrous band that arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, the carpal tunnel, through which the Flexor tendons of the digits and the median nerve pass.It is attached, medially, to the pisiform and the...
through the carpal tunnel
Carpal tunnel
In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...
. It is then lodged between the lateral head of the flexor pollicis brevis and the oblique part of the adductor pollicis, and, entering an osseo
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
aponeurotic
Aponeurosis
Aponeuroses are layers of flat broad tendons. They have a shiny, whitish-silvery color, are histologically similar to tendons, and are very sparingly supplied with blood vessels and nerves. When dissected, aponeuroses are papery, and peel off by sections...
canal similar to those for the flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb.
Relations
The anterior interosseous nerveAnterior interosseous nerve
The anterior interosseous nerve is a branch of the median nerve that supplies the deep muscles on the front of the forearm, except the ulnar half of the flexor digitorum profundus....
(a branch of the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
) and the anterior interosseous artery and vein pass downward on the front of the interosseous membrane between the flexor pollicis longus and flexor digitorum profundus.
Injuries to tendons are particularly difficult to recover from due to the limited blood supply they receive.
Actions
The flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists in flexing the wrist.Variations
Slips may connect with flexor digitorum superficialis, flexor digitorum profundus, or the pronator teres. An additional tendon to the index finger is sometimes found.Evolutionary variation
Modern humans are unique among hominids in having a flexor pollicis longus (FPL) muscle belly that is separate from that of the flexor digitorum profundusFlexor digitorum profundus muscle
- References :...
(FDP). While the FPL is not a separate muscle belly in extant great apes
Great Apes
Great Apes may refer to*Great apes, species in the biological family Hominidae, including humans, chimpanzees, gorillas, and orangutans*Great Apes , a 1997 novel by Will Self...
, a distinct tendon from the FDP belly might be present. In some individuals this tendon tend to act more like a ligament which restricts extension of the interphalangeal joint of the thumb. In orangutan
Orangutan
Orangutans are the only exclusively Asian genus of extant great ape. The largest living arboreal animals, they have proportionally longer arms than the other, more terrestrial, great apes. They are among the most intelligent primates and use a variety of sophisticated tools, also making sleeping...
s there is a tendon similar in insertion and function to the FPL in humans, but which has an intrinsic origin on the oblique head of the adductor pollicis
Adductor pollicis muscle
In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique....
.
Lesser apes (i.e. gibbons) and Old World monkey
Old World monkey
The Old World monkeys or Cercopithecidae are a group of primates, falling in the superfamily Cercopithecoidea in the clade Catarrhini. The Old World monkeys are native to Africa and Asia today, inhabiting a range of environments from tropical rain forest to savanna, shrubland and mountainous...
s (e.g. baboons) share an extrinsic FPL muscle tendon with humans. In most lesser apes the FPL belly is separate from the FDP belly, but in baboons the FPL tendon bifurcates from the FDP tendon at the wrist within the carpal tunnel
Carpal tunnel
In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm. The tunnel consists of bones and connective tissue...
and, because of the lack of differentiation in both the FDP and FPL musculature, it is unlikely that baboons can control individual digits independently.