Extensor digitorum muscle
Encyclopedia
The extensor digitorum muscle (also known as extensor digitorum communis) is a muscle
of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand.
, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the middle and distal phalanges of the fingers in the following manner.
Opposite the metacarpophalangeal articulation each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx
and is reinforced, in this situation, by the tendons of the Interossei
and Lumbricalis
.
Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the Extensor indicis proprius
, which lies on its ulna
r side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateralward to the second tendon, and the other passing from the same tendon downward and medialward to the fourth.
Occasionally the first tendon is connected to the second by a thin transverse band. Collectively, these are known as the sagittal bands; they serve to maintain the central alignment of the extensor tendons over the metacarpal head, thus increasing the available lever
age. Injuries (such as by an external flexion force during active extension) may allow the tendon to dislocate into the intermetacarpal space; the extensor tendon then acts as a flexor and the finger may no longer be actively extended. This may be corrected surgically by using a slip of the extensor tendon to replace the damaged ligamentous band
It acts principally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the Interossei and Lumbricales.
It tends to separate the fingers as it extends them.
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
of the posterior forearm present in humans and other animals. It extends the medial four digits of the hand.
Origin, insertion, and relations
It arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antebrachial fascia. It divides below into four tendons, which pass, together with that of the Extensor indicis propriusExtensor indicis proprius
-External links: - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region"...
, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the middle and distal phalanges of the fingers in the following manner.
Opposite the metacarpophalangeal articulation each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
and is reinforced, in this situation, by the tendons of the Interossei
Interossei
Interossei refer to muscles between certain bones. There are many interossei in a human body. Specific interossei include:-On the hands:* Dorsal interossei muscles of the hand* Palmar interossei muscles-On the feet:...
and Lumbricalis
Lumbricalis
-Species Latin names:* Amphisbaena lumbricalis, Vanzolini, 1996, a worm lizard species in the genus Amphisbaena* Asteriacites lumbricalis, a five-rayed fossil found in rocks : see Asteriacites...
.
Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the Extensor indicis proprius
Extensor indicis proprius
-External links: - "Extensor Region of Forearm and Dorsum of Hand: Deep Muscles of Extensor Region"...
, which lies on its 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...
r side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateralward to the second tendon, and the other passing from the same tendon downward and medialward to the fourth.
Occasionally the first tendon is connected to the second by a thin transverse band. Collectively, these are known as the sagittal bands; they serve to maintain the central alignment of the extensor tendons over the metacarpal head, thus increasing the available lever
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...
age. Injuries (such as by an external flexion force during active extension) may allow the tendon to dislocate into the intermetacarpal space; the extensor tendon then acts as a flexor and the finger may no longer be actively extended. This may be corrected surgically by using a slip of the extensor tendon to replace the damaged ligamentous band
Action
The Extensor digitorum communis extends the phalanges, then the wrist, and finally the elbow.It acts principally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the Interossei and Lumbricales.
It tends to separate the fingers as it extends them.
Additional images
See also
- Extensor digitorum reflexExtensor digitorum reflexThe Extensor digitorum reflex is tested as part of the neurological examination to assess the sensory and motor pathways within the C6 and C7 spinal nerves. It is also known as Braunecker-Effenberg reflex, or BER.-Testing:...
(Braunecker-Effenberg reflex) - Extensor digitorum longus muscleExtensor digitorum longus muscleThe Extensor digitorum longus is a pennate muscle, situated at the lateral part of the front of the leg.-Origin and insertion:It arises from the lateral condyle of the tibia; from the upper three-fourths of the anterior surface of the body of the fibula; from the upper part of the interosseous...
(leg) - Extensor digitorum brevis muscleExtensor digitorum brevis muscleThe extensor digitorum brevis muscle is a muscle on the upper surface of the foot that helps extend digits 2 through 4.-Structure:...
(leg)