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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, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper. The muscles of the thumb include the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, adductor pollicis, and the first dorsal interosseous muscle.
| Characteristics | Values |
|---|---|
| Number of muscles | 9 |
| Muscle groups | 2: intrinsic and extrinsic |
| Intrinsic muscle groups | 4: thenar, hypothenar, interossei, and lumbrical |
| Thenar muscles | abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis |
| Function of thenar muscles | Move the thumb away from the fingers, flex the thumb, and bring the thumb against the fingers |
| Hypothenar muscles | abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi |
| Function of hypothenar muscles | Pull the little finger away from the ring finger, bend the little finger, and bring the little finger towards the thumb |
| Interossei muscles | 4 dorsal and 3 palmar interossei |
| Function of interossei muscles | Spread fingers away from each other and pull fingers together |
| First dorsal interosseous muscle | Assist in thumb adduction |
| Adductor pollicis | Assist in thumb adduction |
| Extrinsic muscles | flexor pollicis longus, abductor pollicis longus, and extensor pollicis longus and brevis |
| Function of extrinsic muscles | Allow for flexion, extension, adduction, abduction, and opposition of the thumb |
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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 flexes the thumb's metacarpal bone
- The adductor pollicis rotates and opposes the thumb
- The first dorsal interosseous assists the adductor pollicis in thumb adduction
The abductor pollicis brevis pulls the thumb away from the index finger
The thumb is moved by 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: extrinsic hand muscles and intrinsic hand muscles. 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.
The three muscles composing the thenar eminence are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger. This is in contrast to the opponens pollicis, which brings the thumb against the fingers, allowing us to grasp objects. 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. It is innervated by the median nerve (C8 and T1).
The abductor pollicis brevis is a particularly important component of muscular anatomy due to its role in opposition of the thumb. The structure of the muscles and joints surrounding the thumb provides increased flexibility and allows for a greater degree of accuracy and precision of movement. This is in contrast to the other fingers, whose structure is less flexible. Injury to the abductor pollicis brevis can be caused by repetitive motion or direct trauma. Common causes include overuse, such as repetitive actions like typing, heavy lifting, and sports, or direct impact, such as a fall or punching something.
The abductor pollicis brevis can be trained to improve its natural range of motion by forcing it to abduct against resistance, such as a small resistance or elastic band. To perform this exercise, hold the elastic band between your two thumbs and keep your hands as still as possible while abducting your thumb out and away from the rest of your hand. It is important to keep the movement smooth and controlled and to adjust the resistance as needed to avoid straining.
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The flexor pollicis brevis bends the thumb toward the small finger
The muscles of the thumb can be divided into two groups: the extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper. The thenar eminence refers to the group of muscles on the palm at the base of the thumb. The three muscles composing the thenar eminence are the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. 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 onto the radial sesamoid bone of the metacarpophalangeal joint.
The hypothenar muscle group is formed by three muscles: the abductor digiti minimi, the flexor digiti minimi, and the opponens digiti minimi. They form the muscle bulk on the small finger side of the hand. The abductor allows the small finger to pull away from the ring finger. The flexor allows the small finger to bend at the MCP joint. The opponens allows us to cup our hands, bringing the small finger towards the thumb. The palmar interossei muscles pull our fingers together.
The first dorsal interosseous muscle is the largest and originates from the 1st and 2nd hand bones. It forms the contour between the thumb and index finger when looking at the top of the hand. In addition to pulling the index finger away from the middle finger, it also pulls the thumb towards the index finger. This action provides strength and stability when pinching.
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The opponens pollicis flexes the thumb's metacarpal bone
The thumb is moved by nine skeletal muscles located in the hand and forearm. These muscles 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 opponens pollicis is one of the three intrinsic thenar muscles, along with the abductor pollicis brevis and the flexor pollicis brevis. The thenar eminence refers to the group of muscles on the palm at the base of the thumb. The opponens pollicis lies deep to the abductor pollicis brevis and laterally to the flexor pollicis brevis.
The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It originates from the flexor retinaculum of the hand and the tubercle of the trapezium. It passes downward and laterally, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side. The opponens pollicis flexes the thumb's metacarpal at the first carpometacarpal joint, cupping the palm.
The opponens pollicis is innervated by the recurrent branch of the median nerve. In 20% of the population, it is innervated by the ulnar nerve. It receives its blood supply from the superficial palmar arch. Opposition of the thumb is a combination of actions that allows the tip of the thumb to touch the tips of the other fingers. This movement is also called apposition, which is a small hand movement consisting of the thumb touching the tips of the other digits.
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The adductor pollicis rotates and opposes the thumb
The adductor pollicis is a muscle in the hand that functions to adduct the thumb, rotating and opposing it. 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 is unique in that it has a two-headed structure, with the oblique head originating at the capitate and the bases of the second and third metacarpals, and the transverse head originating from the volar aspect of the third metacarpal.
The adductor pollicis is one of the intrinsic muscles of the hand, which are located within the hand itself and are responsible for fine motor functions. The ability to adduct the thumb is critical for hand dexterity, as pinching and gripping are the two principal movements that require intact adduction processes. The adductor pollicis is also involved in thumb abduction, along with the first dorsal interosseous muscle.
The adductor pollicis is innervated by the deep branch of the ulnar nerve (C8-T1). Assessment of its function is often used as a diagnostic measure for potential ulnar nerve entrapment at the elbow, as patients with this condition typically present with weakened pinch and grasp strength.
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 facilitate a wide range of thumb movements, contributing to the versatility and dexterity of the human hand.
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The first dorsal interosseous assists the adductor pollicis in thumb adduction
The thumb is moved by nine skeletal muscles located in the hand and forearm. These muscles 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 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 other two muscles that influence the movement of the thumb are the adductor pollicis and the first dorsal interosseous.
The adductor pollicis is a large, triangular muscle with two heads: the transversal head and the oblique head. It lies deeper and more distal to the flexor pollicis brevis. Despite its name, its main action is rotation and opposition, rather than adduction. The muscle is inserted onto the ulnar sesamoid bone of the metacarpophalangeal joint.
The first dorsal interosseous is one of the central muscles of the hand, extending 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 interossei muscles, originating from the first and second hand bones. It forms the contour between the thumb and index finger when looking at the top of the hand.
Trauma, infection, local injections, and even acupuncture can cause fibrosis of the muscles in the first web space of the hand, leading to severe malposition and loss of function of the thumb and index finger. Surgical treatment, such as tenotomy or tendon lengthening, has been successful in correcting this deformity and restoring thumb function.
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