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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 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 can be compared to guy-wires supporting a flagpole; tension from these muscular guy-wires must be provided in all directions to maintain stability in the articulated column formed by the bones of the thumb.
| Characteristics | Values |
|---|---|
| Number of muscles | 9 |
| Muscle groups | 2 (extrinsic hand muscles, intrinsic hand muscles) |
| Location | hand and forearm |
| Function | flexion, extension, adduction, abduction, opposition of the thumb |
| First dorsal interosseous muscle | pulls index finger away from middle finger, pulls thumb towards index finger |
| Thenar muscle group | abductor pollicis brevis, flexor pollicis brevis, opponens pollicis |
| Abductor pollicis brevis function | pulls thumb away from index finger |
| Flexor pollicis brevis function | bends thumb toward the small finger |
| Opponens pollicis function | brings thumb away from fingers to grasp objects |
| Adductor pollicis function | brings thumb towards the index finger |
| Adductor pollicis heads | 2 |
| Abductor pollicis longus | passes through the 1st dorsal compartment of the wrist |
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What You'll Learn
The thenar muscle group
The adductor pollicis muscle is sometimes described together with the thenar muscles when discussing thumb movements. It is a short and broad, fan-shaped muscle of the palm and arises by two muscular heads: oblique and transverse. The adductor pollicis muscle receives its innervation via the deep branch of the ulnar nerve (C8, T1). Its blood supply is provided by the deep palmar arch. The prime function of this muscle is to produce strong adduction of the thumb at the first carpometacarpal joint.
The muscles of the thumb can be divided into two groups: extrinsic hand muscles and intrinsic hand muscles. The thenar muscles are considered intrinsic muscles of the thumb. The thumb musculature dynamically allows for precision pinching and power gripping.
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The hypothenar muscle group
The hypothenar eminence is a muscular protrusion at the base of the little finger. The muscles allow for a variety of movements of the little finger, including flexion, abduction, lateral rotation, and opposition. The abductor digiti minimi muscle is a short muscle that originates from the palmar surface of the pisiform bone and the dorsal aponeurosis. It courses along the ulnar side of the metacarpal bone and inserts into the ulnar aspect of the base of the proximal phalanx of the little finger. The flexor digiti minimi is the second muscle of the hypothenar group, and the opponens digiti minimi lies deep to the other hypothenar muscles.
The opponens digiti minimi originates from the hook of hamate and the associated flexor retinaculum, inserting into the medial margin of metacarpal V. It rotates the metacarpal of the little finger towards the palm, producing opposition. The flexor digiti minimi allows the little finger to bend at the MCP joint. The abductor digiti minimi allows the little finger to pull away from the ring finger.
A fourth muscle, the palmaris brevis, is also located in this region. However, it is typically classified separately as an outstanding superficial muscle of the region. The function of the palmaris brevis is to tighten the palmar aponeurosis and contribute to grip strength. The blood supply for the hypothenar eminence comes mainly from the ulnar artery via the superficial palmar arch.
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The extrinsic hand muscles
The muscles of the thumb can be divided into two groups: the extrinsic hand muscles and the intrinsic hand muscles. The extrinsic hand muscles are those that originate outside the hand but insert into its structures. Most of these muscles have their origins in the forearm, with several also originating from the humerus. They perform the gross movements of the hand and wrist and provide strength.
The extrinsic muscles of the hand are defined by a proximal origin with an insertion on the hand. They can be grouped by anatomy and function. The muscles included in the anterior forearm with insertion on the hand can be further divided into superficial, intermediate, and deep groups. The majority of the muscles in the group are flexor muscles.
The superficial group includes the flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. The flexor carpi ulnaris is innervated by the ulnar nerve, while the flexor carpi radialis and palmaris longus are innervated by the median nerve.
The intermediate group includes the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus. These muscles flex the fingers and thumb, respectively.
The deep group includes the extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris. These muscles extend the fingers and wrist.
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The intrinsic hand muscles
The muscles of the thumb can be divided into two groups: extrinsic hand muscles and intrinsic hand muscles. The intrinsic hand muscles are located within the hand itself and are responsible for the fine motor functions of 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. There are three muscles that compose the thenar eminence: the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger, while the flexor pollicis brevis bends the thumb toward the small finger. The opponens pollicis is the largest of the thenar muscles and performs one of the most important functions of the human hand: the ability to bring the thumb away from the fingers so that we can grasp objects. It helps pull the thumb away from the index finger, while rotating it, so that the tip of the thumb is opposite, or “opposes,” the tips of the other fingers.
The other two muscles that influence the movement of the thumb are the adductor pollicis and the first dorsal interosseous muscle. 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.
The hypothenar muscles form the hypothenar eminence, a muscular protrusion on the medial side of the palm, at the base of the little finger. 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 little finger to pull away from the ring finger, while the flexor allows the little finger to bend at the MCP joint.
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The first dorsal interosseous muscle
The dorsal interosseous muscles are bipennate, with each muscle arising by two heads from the adjacent sides of the metacarpal bones, but more extensively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the proximal phalanges and into the extensor expansion of the corresponding extensor digitorum tendon. The first dorsal interosseous muscle is larger than the others, and the radial artery passes between its two heads from the back of the hand into the palm.
The main function of the dorsal interossei is to abduct the fingers 2-4 in a longitudinal axis, moving them away from each other. The first dorsal interosseous muscle receives vascular supply from the first dorsal metacarpal branch of the radial artery.
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Frequently asked questions
The muscles near the thumb include the thenar muscles, hypothenar muscles, interossei muscles, and lumbrical muscles.
The thenar muscles, which are three short muscles located at the base of the thumb, are responsible for the fine movements of the thumb. The hypothenar muscles line the outer edges of the palm on the outside of the pinky finger and control the area of the hand opposite the thumb. The interossei muscles are between the metacarpal bones in the palm and help the fingers move side-to-side. The lumbrical muscles are at the base of the four non-thumb fingers and help flex the fingers.
The muscles acting on the thumb can be divided into two groups: extrinsic hand muscles and intrinsic hand muscles. An example of an extrinsic hand muscle is the flexor pollicis longus, which allows us to bend the tip of our thumb. The thenar eminence, a group of intrinsic hand muscles, includes the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.
