The lumbricals are intrinsic

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s 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 ...

that

flex Flex or FLEX may refer to: Computing * Flex (language), developed by Alan Kay * FLEX (operating system), a single-tasking operating system for the Motorola 6800 * FlexOS, an operating system developed by Digital Research * FLEX (protocol), a comm ...

the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

s, and extend the

interphalangeal joints Interphalangeal joint may refer to: *Interphalangeal articulations of hand The interphalangeal joints of the hand are the hinge joints between the phalanges of the fingers that provide flexion towards the palm of the hand. There are two sets in ...

. p. 97 The lumbrical muscles of the foot also have a similar action, though they are of less clinical concern.

Structure

The lumbricals are four, small, worm-like muscles on each hand. These muscles are unusual in that they do not attach to bone. Instead, they attach proximally to the tendons of

flexor digitorum profundus The flexor digitorum profundus is a muscle in the forearm of humans that flexes the fingers (also known as digits). It is considered an extrinsic hand muscle because it acts on the hand while its muscle belly is located in the forearm. Together t ...

, and distally to the

extensor expansion An extensor expansion (extensor hood, dorsal expansion, dorsal hood, dorsal aponeurosis) is the special connective attachments by which the extensor tendons insert into the phalanges. These flattened tendons (aponeurosis) of extensor muscles sp ...

s. The first and second lumbricals are

unipennate Muscle architecture is the physical arrangement of muscle fibers at the macroscopic level that determines a muscle’s mechanical function. There are several different muscle architecture types including: parallel, pennate and hydrostats. Force pr ...

, while the third and fourth lumbricals are

bipennate Muscle architecture is the physical arrangement of muscle fibers at the macroscopic level that determines a muscle’s mechanical function. There are several different muscle architecture types including: parallel, pennate and hydrostats. Force pr ...

1121 Intrinsic Muscles of the Hand Superficial sin

Nerve supply

The first and second lumbricals (the most radial two) are

innervated A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

by the

median nerve The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus. The median nerve originates from the lateral and medial cords of the brachial plexus, and has contr ...

. The third and fourth lumbricals (most ulnar two) are innervated by the deep branch of

ulnar nerve In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is ...

. This is the usual innervation of the lumbricals (occurring in 60% of individuals). However 1:3 (median:ulnar - 20% of individuals) and 3:1 (median:ulnar - 20% of individuals) also exist. The lumbrical innervation always follows the innervation pattern of the associated muscle unit of

(i.e. if the muscle units supplying the

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...

to the

middle finger The middle finger, long finger, second finger, third finger, toll finger or tall man is the third digit of the human hand, located between the index finger and the ring finger. It is typically the longest digit. In anatomy, it is also called ...

are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve).

Blood supply

Four separate sources supply blood to these muscles: the

superficial palmar arch The superficial palmar arch is formed predominantly by the ulnar artery, with a contribution from the superficial palmar branch of the radial artery. However, in some individuals the contribution from the radial artery might be absent, and instea ...

, the

common palmar digital artery Three common palmar digital arteries arise from the convexity of the superficial palmar arch and proceed distally on the second, third, and fourth lumbricales muscles. Alternative names for these arteries are: common volar digital arteries, ul ...

, the

deep palmar arch The deep palmar arch (deep volar arch) is an arterial network found in the palm. It is usually primarily formed from the terminal part of the radial artery. The ulnar artery also contributes through an anastomosis. This is in contrast to the supe ...

, and the dorsal digital artery.

Function

The lumbrical muscles, with the help of the interosseous muscles, simultaneously flex the

s while extending both interphalangeal joints of the digit on which it inserts. The lumbricals are used during an upstroke in writing.

Etymology

The term "lumbrical" comes from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

, meaning "

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

Additional images

File:Gray416.png, Tendons of forefinger and vincula tendina File:Slide2yyy.JPG, Lumbricals of the hand File:Slide5RRR.JPG, Lumbricals of the hand File:Slide14RRR.JPG, Lumbricals muscle File:Slide6PPP.JPG, Lumbricals muscle File:Slide4VVV.JPG, Lumbricals muscle File:Slide4AAAA.JPG, Lumbricals muscle File:Slide9AAAA.JPG, Lumbricals muscle File:Slide1MAI.JPG, Muscles of hand, cross section File:Slide1dsds.JPG, Wrist joint. Deep dissection.Anterior, palmar view File:Slide2dsds.JPG, Wrist joint. Deep dissection.Anterior, palmar view File:Slide3dsds.JPG, Wrist joint. Deep dissection.Anterior, palmar view

References

{{Authority control Muscles of the upper limb Hand