Maximus Gage
The muscles of the thumb are nine skeletal muscles located in the hand and forearm. These muscles allow for flexion, extension, adduction, abduction, and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: the extrinsic hand muscles and the intrinsic hand muscles. The flexor pollicis brevis is a two-headed muscle that arises on the flexor retinaculum and originates on three carpal bones: the trapezium, trapezoid, and capitate. It acts to flex, adduct, and abduct the thumb, allowing humans to grasp objects and apply pressure with their thumb.
| Characteristics | Values |
|---|---|
| Number of muscles in the thumb | 9 |
| Muscle groups | Extrinsic hand muscles, intrinsic hand muscles, thenar eminence, and other muscles |
| Muscles that flex the thumb | Flexor pollicis longus, flexor pollicis brevis, opponens pollicis |
| Where the flexor pollicis brevis muscle is located | In the hand itself |
| Where the flexor pollicis longus muscle is located | In the forearm |
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What You'll Learn
Flexor pollicis longus
The flexor pollicis longus is a long muscle in the forearm and hand that flexes the thumb. It is unique to humans, being either rudimentary or absent in other primates. It is the ninth tendon to pass through the carpal tunnel on its way to the thumb.
The flexor pollicis longus is supplied by the anterior interosseous (C8-T1) branch of the median nerve (C5-T1). It receives dual blood supply. Its medial part is supplied by the anterior interosseous artery, an indirect branch of the ulnar artery, while the lateral part receives blood from the radial artery. The muscle may also receive contributions from the median artery if it is well developed.
The main function of the flexor pollicis longus is flexion of the thumb at the interphalangeal joint, which is essential for gripping. It is the only muscle that flexes the interphalangeal joint of the thumb, making it vital for activities requiring hand grip.
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Flexor pollicis brevis
The flexor pollicis brevis is a short, broad intrinsic muscle of the hand. It is one of the three muscles that make up the thenar eminence, a group of muscles on the palm at the base of the thumb. The other two muscles in the thenar eminence are the abductor pollicis brevis and the opponens pollicis.
The flexor pollicis brevis is a two-headed muscle, consisting of a superficial head and a deep head. The superficial head arises on the flexor retinaculum, while the deep head originates on three carpal bones: the trapezium, trapezoid, and capitate. The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint.
The flexor pollicis brevis acts to flex, adduct, and abduct the thumb, allowing it to curl up into the palm. It also assists in opposition and medial rotation of the thumb. This muscle receives its blood supply from the superficial palmar branches of the radial artery.
The two heads of the flexor pollicis brevis usually differ in their innervation. The superficial head receives its nervous supply from the recurrent branch of the median nerve, while the deep head is innervated by the deep branch of the ulnar nerve (C8-T1). Due to a common interconnection between the median and ulnar nerves in the hand (known as the Riche-Cannieu interconnection), the median nerve may innervate the flexor pollicis brevis in approximately 35% of people.
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Abductor pollicis brevis
The abductor pollicis brevis is a thenar muscle located within the hand. It is a flat, thin muscle found directly underneath the skin at the surface of the thenar eminence. The thenar eminence is a group of three muscles—abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis—that form an elevation on the radial (lateral) aspect of the palm. The abductor pollicis brevis is the most lateral and superficial of the thenar muscles.
The abductor pollicis brevis originates from the flexor retinaculum of the hand, the tubercle of the scaphoid bone, and sometimes the tubercle of the trapezium. It runs laterally and downward and is inserted by a thin, flat tendon into the radial side of the base of the first phalanx of the thumb. The muscle ends in a flat tendon that inserts into the capsule of the metacarpophalangeal joint.
The primary function of the abductor pollicis brevis is the abduction of the thumb, which is the movement of the thumb away from the other fingers or anteriorly, perpendicular to the palm. This action occurs at the carpometacarpal joint and the metacarpophalangeal joint. The abductor pollicis brevis also facilitates the movement of the thumb towards the fingertips in the carpometacarpal joint (opposition) and flexion in the metacarpophalangeal joint.
The abductor pollicis brevis is innervated by the recurrent (thenar) branch of the median nerve (C8-T1). It is vascularized by the superficial palmar branch, which arises from the radial artery.
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Opponens pollicis
The opponens pollicis is a small, triangular muscle in the hand, which is the largest of the three thenar muscles. It originates from the flexor retinaculum of the hand and the tubercle of the trapezium bone and inserts into the whole length of the metacarpal bone of the thumb on its radial side. It lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis. The opponens pollicis is innervated by the recurrent branch of the median nerve and, in 20% of the population, by the ulnar nerve. Its blood supply comes from the superficial palmar branch of the radial artery, with additional supply from other arteries.
The main function of the opponens pollicis is to oppose the thumb, bringing it against the fingers. This is a complex movement that involves flexion, adduction, and medial rotation at the first carpometacarpal joint, allowing the tip of the thumb to touch the tips of the other fingers. This movement is crucial for human hand dexterity, enabling us to grasp objects and perform precise actions such as gripping a pencil.
The opponens pollicis is one of the intrinsic muscles of the thumb, specifically a part of the thenar eminence group of muscles located at the base of the thumb. This group includes the abductor pollicis brevis, which pulls the thumb away from the index finger, and the flexor pollicis brevis, which bends the thumb toward the small finger. The opponens pollicis works in conjunction with these muscles to allow for a wide range of thumb movements and dexterity.
The flexion of the thumb's metacarpal at the first carpometacarpal joint, also known as apposition, is a specific action that cups the palm. While the opponens pollicis plays a role in this movement, true apposition requires the coordination of several other muscles at the thumb's metacarpophalangeal joint. This coordination allows for the precise and versatile movements that the human hand is capable of.
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Adductor pollicis
The adductor pollicis is an intrinsic muscle of the hand, which means it lies in the deepest muscular plane of the palm, within the adductor compartment. It is a unique muscle, with a two-headed structure: the transverse head and the oblique head. The transverse head is deeply seated and triangular, arising from the lower two-thirds of the palmar surface of the third metacarpal bone. The oblique head originates at the capitate, as well as the bases of the second and third metacarpals. These two heads then merge as the fibres travel laterally, forming the tendon of the adductor pollicis, which often contains a sesamoid bone.
The adductor pollicis is the most powerful of the intrinsic muscles of the hand. Its main function is the adduction of the thumb, which is the movement of the thumb towards the index finger from an abducted position. This action is critical for hand dexterity, enabling pinching and gripping. The adductor pollicis also aids in the later stages of opposition of the thumb, which is the combination of adduction, medial rotation, flexion, and adduction of the thumb so that it can touch each fingertip of the same hand.
The adductor pollicis is innervated by the deep branch of the ulnar nerve (C8-T1). The deep palmar arterial arch is the main blood supply to the adductor pollicis, formed by the anastomosis of the radial artery and the deep palmar branch of the ulnar artery. The radial artery passes between the two heads of the adductor pollicis, travelling from the back of the hand into the palm, where it forms the deep palmar arch.
The adductor pollicis is a significant anatomical landmark for the radial artery. As the radial artery enters the hand, it passes through the two heads of the first dorsal interosseous muscle and then proceeds to pass anteromedially between the two heads of the adductor pollicis.
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Frequently asked questions
The muscles that flex the thumb are the flexor pollicis longus, flexor pollicis brevis, and opponens pollicis.
The flexor pollicis brevis and opponens pollicis muscles are located in the hand itself, forming the thenar eminence or thenar pad.
The flexor pollicis brevis flexes the thumb, allowing it to curl up in the palm and bend toward the small finger. It also assists in thumb abduction and adduction.
The opponens pollicis muscle opposes the thumb, bringing it against the fingers. This movement is crucial for human hand dexterity and grip.
