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The thumb is moved by a complex interplay of many muscles, tendons, and fascial compartments. There are nine muscles in total that contribute to the movement of the thumb, which can be divided into two groups: extrinsic (muscles in the forearm) and intrinsic (muscles in the hand). The extrinsic muscles include the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and flexor pollicis longus. The intrinsic muscles include the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, adductor pollicis, and first dorsal interosseous muscle. These muscles allow for flexion, extension, adduction, abduction, and opposition of the thumb, giving the hand its versatility and dexterity.
| Characteristics | Values |
|---|---|
| Number of muscles that move the thumb | 9 |
| Groups | Extrinsic (4 muscles in the forearm) and intrinsic (5 muscles in the hand) |
| Extrinsic muscles | Abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, flexor pollicis longus |
| Intrinsic muscles | Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, adductor pollicis, first dorsal interosseous |
| Function of abductor pollicis brevis | Moves the thumb away from the other four fingers |
| Function of flexor pollicis brevis | Flexes the thumb, curling it up in the palm |
| Function of opponens pollicis | Brings the thumb against the fingers |
| Function of adductor pollicis | Thumb rotation and opposition |
| Function of first dorsal interosseous | Pulls the thumb towards the index finger |
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What You'll Learn
- The abductor pollicis brevis pulls the thumb away from the index finger
- The flexor pollicis brevis bends the thumb toward the small finger
- The opponens pollicis opposes/adducts the thumb
- The adductor pollicis is an intrinsic muscle of the hand
- The first dorsal interosseous muscle lies between the thumb and the first metacarpal
The abductor pollicis brevis pulls the thumb away from the index finger
The abductor pollicis brevis is a muscle that pulls the thumb away from the index finger. It is one of the intrinsic muscles of the thumb, which are the muscles located within the hand itself. The intrinsic muscles of the thumb can be further divided into two groups: the thenar eminence and other muscles. The thenar eminence refers to the group of muscles on the palm at the base of the thumb, which includes the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
The abductor pollicis brevis is the most superficial muscle in the thenar group. It originates on the scaphoid tubercle and the flexor retinaculum and inserts into the radial sesamoid bone and the proximal phalanx of the thumb. The function of the abductor pollicis brevis is to abduct the thumb, moving it away from the other four fingers. This is in contrast to the function of the flexor pollicis brevis, which lies next to the abductor pollicis brevis and is responsible for flexing the thumb, curling it up into the palm.
The opponens pollicis is another muscle in the thenar eminence group that lies deep to the abductor pollicis brevis. It opposes the thumb, bringing it against the fingers, which is important for most of the human hand's dexterity and grip strength. The first dorsal interosseous muscle is also involved in thumb movement and lies between the thumb and the first metacarpal (index finger). It primarily acts upon the index finger but also assists in thumb adduction.
The abductor pollicis brevis is an important muscle for the movement of the thumb and allows for the thumb to be moved away from the index finger and other fingers. This movement is essential for the hand's dexterity and grip strength, allowing for complex and intricate motions. The abductor pollicis brevis is a key muscle in the intricate musculature of the hand, which includes several layers of muscles, tendons, and fascial compartments that work together to enable a wide range of thumb and hand movements.
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The flexor pollicis brevis bends the thumb toward the small finger
The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles allow for flexion, extension, adduction, abduction, and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: extrinsic hand muscles and intrinsic hand muscles. The extrinsic hand muscles have their muscle bellies located in the forearm, while the intrinsic hand muscles have their muscle bellies located in the hand.
The intrinsic muscles of the thumb can be further divided into two groups: the thenar eminence and other muscles. The thenar eminence refers to the group of muscles on the palm at the base of the thumb, which includes the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The flexor pollicis brevis, which lies next to the abductor pollicis brevis, is responsible for flexing the thumb, bending it toward the small finger.
The flexor pollicis brevis is a two-headed muscle. 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 into the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. The flexor pollicis brevis is one of the most important muscle-tendon units of the thumb, allowing for most of the hand's dexterity, including grip.
The hypothenar muscle group, which forms the muscle bulk on the small finger side of the hand, is composed of three muscles: the abductor digiti minimi, the flexor digiti minimi, and the opponens digiti minimi. The abductor digiti minimi allows the small finger to pull away from the ring finger, the flexor digiti minimi allows the small finger to bend at the MCP joint, and the opponens digiti minimi allows us to cup our hands, bringing the small finger towards the thumb.
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The opponens pollicis opposes/adducts the thumb
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, which are a group of muscles on the palm at the base of the thumb. The other two thenar muscles are the abductor pollicis brevis and the flexor pollicis brevis. The opponens pollicis lies deep to the abductor pollicis brevis and laterally to the flexor pollicis brevis.
Opposition is a small hand movement consisting of the thumb touching the tips of the other digits. This movement allows the hand to cup objects and make a pincher grip. The opponens pollicis contracts to pull the thumb medially towards the other digits, which is a combination of flexion, internal rotation, and palmar abduction of the thumb.
The opponens pollicis originates from the tubercle of the trapezium and the flexor retinaculum. It passes downward and laterally, inserting into the whole length of the metacarpal bone of the thumb on its radial side. The blood supply and nerve innervation to the opponens pollicis muscle originate from the recurrent branch of the median nerve. Any damage to either the nerve innervation or blood supply proximally can result in damage to the opponens pollicis muscle.
The adductor pollicis is another muscle that contributes to the opposition of the thumb. It lies deeper and more distal to the flexor pollicis brevis and has two heads: transversal and oblique. The adductor pollicis muscle is an intrinsic muscle of the hand, which lies in the deepest muscular plane of the palm, within the adductor compartment.
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The adductor pollicis is an intrinsic muscle of the hand
The adductor pollicis has two heads: the oblique head and the transverse head. The oblique head is also called the adductor obliquus pollicis muscle, and the transverse head is also known as the adductor transversus pollicis muscle. The transverse head originates from the palmar base of the third metacarpal bone, while the oblique head originates from the capitate bone and palmar bases of the second and third metacarpals. The muscle fibres from these two origins converge into one muscle belly as they run laterally towards the thumb.
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 essential for pinching and gripping. The adductor pollicis also aids in the later stages of opposition of the thumb, which is the movement of the thumb touching each fingertip of the same hand. This movement is a combination of adduction, medial rotation, flexion, and adduction of the thumb.
The strength of the adductor pollicis can be tested by pushing the thumb against the index finger while trying to pull them apart. This muscle is innervated by the deep branch of the ulnar nerve (C8-T1). The adductor pollicis is larger and deeper than the thenar muscles. On its ventral aspect, it is crossed by the flexor tendons of the index finger, first lumbrical, and flexor pollicis brevis muscles. On its dorsal aspect, it is related to or sometimes conjoined with the first dorsal interosseous muscle.
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The first dorsal interosseous muscle lies between the thumb and the first metacarpal
The thumb is moved by a diverse set of muscles within the hand. One of the central muscles of the hand that influences the movement of the thumb is the first dorsal interosseous muscle. This muscle lies between the thumb and the first metacarpal.
The first dorsal interosseous muscle is one of four dorsal interosseous muscles, which are short bipennate intrinsic muscles of the hand. They are found on the dorsal aspect of the hand, occupying the space between the metacarpal bones. The first dorsal interosseous muscle extends from the base of the thumb metacarpal to the radial side of the proximal phalanx of the index finger. It is the largest of the four dorsal interosseous muscles.
The first dorsal interosseous muscle is inserted into the base of the proximal phalanx of the index finger and into the extensor expansion of the corresponding extensor digitorum tendon. It is innervated by the deep branch of the ulnar nerve. The muscle receives its vascular supply from the first dorsal metacarpal branch of the radial artery, which passes between its two heads.
The main function of the first dorsal interosseous muscle is to abduct the index finger, moving it away from the middle finger. It also pulls the thumb towards the index finger, providing strength and stability when pinching. In addition, the first dorsal interosseous muscle can rotate the index finger slightly at the metacarpophalangeal joint and assist the adductor pollicis in thumb adduction.
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