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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 flexor pollicis brevis is a two-headed muscle that flexes the thumb at the metacarpophalangeal joint. The flexor pollicis longus is a long, deep muscle that also flexes the thumb. The abductor pollicis brevis pulls the thumb away from the index finger, while the opponens pollicis opposes the thumb, bringing it against the fingers. These muscles, along with others, work together to allow for the flexion, extension, adduction, abduction, and opposition of the thumb, enabling movements such as grasping and applying pressure.
| Characteristics | Values |
|---|---|
| Number of muscles in the thumb | 9 |
| Muscle groups | Extrinsic hand muscles, Intrinsic hand muscles |
| Muscle bellies of extrinsic hand muscles | Located in the forearm |
| Muscle bellies of intrinsic hand muscles | Located in the hand |
| Functions of the thumb muscles | Flexion, Extension, Adduction, Abduction, Opposition of the thumb |
| Muscle that pulls the thumb away from the index finger | Abductor pollicis brevis |
| Muscle that bends the thumb toward the small finger | Flexor pollicis brevis |
| Muscle that brings the thumb away from the fingers to grasp objects | Opponens pollicis |
| Muscle that flexes the tip of the thumb | Flexor pollicis longus |
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What You'll Learn
The flexor pollicis brevis flexes the thumb
The flexor pollicis brevis is a muscle that flexes the thumb. It is one of the intrinsic muscles of the thumb, located within the hand itself. Specifically, it is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. This muscle is part of a group of muscles called the thenar eminence or thenar muscle group. The thenar eminence is a group of muscles on the palm at the base of the thumb, including the abductor pollicis brevis, the opponens pollicis, and the flexor pollicis brevis.
The flexor pollicis brevis is a two-headed muscle, with one head arising on the flexor retinaculum and the other originating on three carpal bones: the trapezium, trapezoid, and capitate. The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. By flexing the thumb, the flexor pollicis brevis also enables adduction, abduction, and opposition of the thumb. This muscle works together with the flexor pollicis longus tendon, which is the longer tendon of the two, to allow for thumb flexion and grasping.
The flexor pollicis brevis is the smallest and most distal of the thenar muscles. Despite its small size, it plays a crucial role in hand dexterity and grip strength. The ability to bring the thumb towards the fingers and grasp objects is largely dependent on the function of this muscle. The flexor pollicis brevis is also involved in the flexion and medial rotation of the first metacarpal bone at the carpometacarpal joint.
Injuries to the flexor pollicis brevis muscle can occur, especially in new mothers who frequently lift their infants and small children under their armpits. As the child grows, the action of lifting them under the armpits can strain the pollicis tendons, including the flexor pollicis brevis. It is important to be aware of the potential for injury and to understand the anatomy of the thumb muscles for effective injury assessment and treatment.
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The flexor pollicis longus flexes the thumb
The thumb is moved by nine skeletal muscles, which are located in the hand and forearm. These muscles enable flexion, extension, adduction, abduction, and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: extrinsic hand muscles, with their muscle bellies located in the forearm, and intrinsic hand muscles, with their muscles bellies located in the hand.
The flexor pollicis longus is a long, deep muscle that arises from the mid-forearm from the radial shaft. It is responsible for flexing the thumb, allowing us to bend the tip of our thumb. It is the ninth tendon to pass through the carpal tunnel on its way to the thumb. The flexor pollicis longus is located deep in the forearm, and four tendons emerge from the muscle, which pass through the carpal tunnel and insert into the tips of the index, middle, ring, and small fingers.
The flexor pollicis brevis is another muscle that flexes the thumb. It is the smallest and most distal of the thenar muscles. It originates from the wrist and attaches to the thumb. The flexor pollicis brevis is a two-headed muscle, with the superficial head arising on the flexor retinaculum, and the deep head originating on three carpal bones: the trapezium, trapezoid, and capitate. It inserts into the radial sesamoid bone of the metacarpophalangeal joint.
The flexor pollicis brevis is also capable of flexing, abducting, and adducting the thumb, and therefore assists in opposing the thumb. The opponens pollicis is another muscle that opposes the thumb, bringing it against the fingers. This is a very important movement, as most of the human hand's dexterity, including grip, comes from this action.
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The abductor pollicis brevis moves the thumb away from fingers
The abductor pollicis brevis (APB) is a small muscle in the hand that moves the thumb away from the fingers. 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 are the flexor pollicis brevis and the opponens pollicis.
The APB originates from the flexor retinaculum of the hand, the tubercle of the scaphoid bone, and sometimes the tubercle of the trapezium. It inserts via a small tendon into the lateral side of the base of the first phalanx of the thumb and the metacarpophalangeal joint. This allows the APB to abduct the thumb, moving it away from the fingers.
The APB also plays a role in opposing the thumb, which is the movement that brings the thumb against the fingers. This is a crucial function for human hand dexterity and grip. The opponens pollicis muscle assists in this movement by helping to pull the thumb away from the fingers and rotate it so that the tip of the thumb is opposite the tips of the other fingers.
The flexor pollicis brevis, which lies next to the APB, also contributes to thumb movement. It flexes the thumb, curling it up towards the palm, and bends it towards the small finger. Additionally, the flexor pollicis longus, arising from the mid-forearm, allows us to bend the tip of the thumb.
Injury to the APB can occur due to repetitive motion or direct trauma. Common causes include overuse through repetitive actions such as typing, heavy lifting, or sports, as well as direct impacts like falling or punching.
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The opponens pollicis opposes the thumb, bringing it against fingers
The opponens pollicis muscle is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles, which are found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. The opponens pollicis muscle originates from the flexor retinaculum of the hand and the tubercle of the trapezium bone. It then passes downward and laterally, inserting into the whole length of the metacarpal bone of the thumb on its radial side.
The main function of the opponens pollicis muscle is to oppose the thumb, bringing it against the fingers. This movement is known as opposition and refers to the complex movement of the thumb, which is a combination of flexion, adduction, and medial rotation at the first carpometacarpal joint. This allows the tip of the thumb to touch the tips of the other fingers, enabling precise and efficient movements of the hand, such as grasping objects or fine gripping of a pencil.
The opponens pollicis muscle works in conjunction with other muscles in the hand and forearm to produce this opposition movement. For example, the lumbrical muscles, flexor digitorum superficialis muscle, and flexor digitorum profundus muscle contract during the opposition of the hand, allowing the thumb to touch the tips of the second, third, and fourth digits. Additionally, the abductor pollicis brevis muscle, another thenar muscle, pulls the thumb away from the index finger, while the flexor pollicis brevis muscle bends the thumb toward the small finger.
The nerve innervation of the opponens pollicis muscle typically comes from the recurrent branch of the median nerve, but in some cases, it may also be innervated by the ulnar nerve. This variation in nerve innervation is important to consider during hand surgery to avoid damage to these structures. Overall, the opponens pollicis muscle plays a crucial role in the dexterity and functionality of the human hand.
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The adductor pollicis is responsible for thumb adduction
The muscles of the thumb are nine skeletal muscles located in the hand and forearm. These muscles enable flexion, extension, adduction, abduction, and opposition of the thumb. The muscles acting on the thumb are divided into two groups: extrinsic hand muscles and intrinsic hand muscles. The former has muscle bellies located in the forearm, while the latter has muscle bellies in the hand.
The adductor pollicis is an intrinsic muscle of the hand and is responsible for thumb adduction. It is a fleshy, flat, triangular, and fan-shaped muscle deep in the thenar compartment beneath the long flexor tendons and the lumbrical muscles at the center of the palm. It has two heads: transverse and oblique. The radial artery passes through the space between the two heads to form the deep palmar arch. 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. Both heads attach to the base of the proximal phalanx of the thumb.
The adductor pollicis is the most powerful of the intrinsic muscles of the hand. Its primary 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 crucial for functions requiring pinching and gripping. Additionally, the adductor pollicis aids in the later stages of thumb opposition, a movement that combines adduction, medial rotation, flexion, and adduction of the thumb to touch each fingertip of the same hand.
The thenar eminence refers to the group of muscles on the palm at the base of the thumb, including the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. These muscles work together with the adductor pollicis to enable a range of thumb movements and provide dexterity and grip strength.
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Frequently asked questions
The muscles involved in flexing the thumb include the flexor pollicis longus, flexor pollicis brevis, and opponens pollicis.
The flexor pollicis longus is a long, deep muscle that originates near the elbow and flexes the thumb, allowing for grasping and applying pressure.
The flexor pollicis brevis is a short muscle located in the hand that flexes the thumb, curling it towards the palm. It also contributes to abduction, adduction, and opposition of the thumb.
The opponens pollicis is a small, triangular muscle that flexes the thumb's metacarpal bone, allowing the thumb to oppose the fingers and improving grip.
