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The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. There are over 30 muscles in the hand, working together to allow movement. The muscles that control finger motion are located in the hand and forearm. The fingers have two long flexors, located on the underside of the forearm, which attach to the phalanges of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The extensors are located on the back of the forearm and are connected to the dorsum of the fingers. The extensors are responsible for straightening out the digits. The muscles in the hand and forearm work together to allow the fingers to move.
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What You'll Learn
The flexors and extensors
The muscles that control finger movement are located in the forearm and hand. The fingers themselves do not contain any muscles. The muscles in the forearm that control finger movement are called extensor digitorum communis and flexor digitorum profundus. These muscles originate near the elbow, run through the forearm, and insert into the fingers via tendons. The extensors are located on the back of the forearm, while the flexors are located on the underside of the forearm.
The extensors' primary function is to straighten out the fingers. The thumb has two extensors in the forearm, and the index finger and little finger have an extra extensor, used for pointing, for instance. The extensors are situated within six separate compartments. The first four compartments are located in the grooves on the dorsum of the inferior side of the radius, while the fifth compartment is between the radius and ulna. The sixth compartment is in the groove on the dorsum of the inferior side of the ulna.
The flexors allow for the actual bending of the fingers. There are two long flexors, located on the underside of the forearm. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The thumb has one long flexor and a short flexor in the thenar muscle group. The thenar muscle group is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. It consists of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger, and the flexor pollicis brevis bends the thumb toward the small finger.
The interossei muscles are between the metacarpal bones in the hand 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 lumbricals also help to extend the PIP joints. 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, and the opponens allow us to cup our hands, bringing the small finger toward the thumb.
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Interossei muscles
The interossei muscles are a group of muscles found near the metacarpal bones that help control the fingers. They are considered voluntary muscles. There are four dorsal and three palmar interossei muscles. The dorsal interossei muscles are short, bipennate (feather-like) 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 is the largest and originates 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.
The dorsal interossei muscles consist of four short muscles that attach to the adjacent sides of metacarpals one to four. Their function is to abduct the digits two to four, moving them away from each other. They also assist in flexion at the metacarpophalangeal (MCP) joints and in extension at the interphalangeal (IP) joints. The first and second dorsal interossei muscles pull the second and third digits laterally (radial abduction). The first dorsal interosseous muscle can be easily felt in the web between the thumb and index finger.
The palmar interossei muscles, on the other hand, adduct the digits towards the third digit (towards an imaginary axial line that goes down the middle of the third digit). They are unipennate. Both sets of muscles are innervated by the deep branch of the ulnar nerve.
The interossei muscles are part of the intrinsic muscle groups of the hand. These muscles are smaller muscles located within the various hand osseofascial compartments within the anatomic confines of the wrist and phalanges. The intrinsics are important for various hand functions, such as pinch and grip strength.
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Lumbrical muscles
The lumbrical muscles are a set of four intrinsic hand muscles on each hand that help control the fine and delicate movements of the fingers. They are deep muscles that do not attach to bones. Instead, they attach proximally to the tendons of the flexor digitorum profundus (FDP) and distally to the extensor expansions. Each finger is connected to two lumbricals, except for the thumb, which is associated with only the first lumbrical muscle.
The lumbricals are cylindrical and worm-like, resembling earthworms of the genus Lumbricus, from which they get their name. They are unusual in that they have a high number of muscle spindles, indicating that they play a role in proprioception and sensory feedback, which is important for precision pinch movements and the manipulation of objects. The lumbricals also help in gripping objects, typing, and performing various dexterous hand movements.
The lumbricals flex the metacarpophalangeal (MCP) joints and extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. They work in coordination with other hand muscles, including the interosseous muscles, which help in simultaneously flexing the MCP joints and extending the interphalangeal joints. The lumbricals are innervated by the median nerve and the ulnar nerve, with the lateral two lumbricals typically innervated by the median nerve and the medial two lumbricals by the ulnar nerve.
The lumbrical muscles are located deep in the palm and are essential for the fingers' precision grip and fine motor control. They are supplied by four arteries: the superficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery. The corresponding veins drain into the cephalic vein on the hand's lateral side and the basilic vein on the medial aspect.
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Thenar and hypothenar muscles
The thenar and hypothenar muscles are intrinsic muscles of the hand, located within the hand itself. They are responsible for the fine motor functions of the hand. The muscles of the thenar and hypothenar eminence, along with the adductor compartment, make up the intrinsic muscles of the hand. Their origin and insertion are within the carpal and metacarpal bones and are surrounded by ligaments and fascia of the hand.
The thenar muscle group is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. It consists of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger, and the flexor pollicis brevis bends the thumb toward the small finger. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. It originates from the tubercle of the trapezium and the associated flexor retinaculum and inserts onto the lateral margin of the first metacarpal. It opposes the thumb by medially rotating and flexing the metacarpal on the trapezium.
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 digiti minimi is the most superficial of the hypothenar muscle group. It originates from the pisiform and the tendon of the flexor carpi ulnaris and attaches to the base of the proximal phalanx of the little finger. It abducts the little finger. The flexor digiti minimi brevis lies laterally to the abductor digiti minimi in the hand. It originates from the hook of hamate and adjacent flexor retinaculum and inserts into the base of the proximal phalanx of the little finger. It flexes the metacarpophalangeal joint of the little finger. The opponens digiti minimi muscle moves the little finger to allow the opposition of the hand, in which the pad of the thumb touches the pad of the little finger.
Loss of thenar and hypothenar muscles results in palmar atrophy and weakness in thumb and pinky finger abduction, flexion, and opposition. In Carpal Tunnel Syndrome (CTS), where median nerve compromise occurs, thenar muscles can show wasting as they are innervated by the median nerve. The hypothenar eminence is innervated by the ulnar nerve.
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Abduction and adduction
The movement of the fingers is made possible by the skeletal muscles of the hand, which can be divided into two groups: extrinsic and intrinsic muscles. The extrinsic muscles are those with muscle bellies that originate in the forearm. The intrinsic muscles, on the other hand, are smaller muscles located within the hand and wrist compartments. These muscles are crucial for various hand functions, including pinch and grip strength.
The intrinsic muscle groups include the thenar and hypothenar muscles. The thenar muscle group is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. It consists of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The abductor pollicis brevis pulls the thumb away from the index finger, while the flexor pollicis brevis bends the thumb towards the small finger. This movement of the thumb allows for pinching and grasping actions.
The hypothenar muscle group, on the other hand, is formed by three muscles: the abductor digiti minimi, the flexor digiti minimi, and the opponens digiti minimi. These muscles form the bulk on the small finger side of the hand. The abductor digiti minimi allows the small finger to pull away from the ring finger, while the flexor digiti minimi enables the small finger to bend at the MCP joint. The opponens digiti minimi allows us to cup our hands by bringing the small finger towards the thumb.
The interossei muscles are another group of intrinsic muscles that play a role in finger movement. There are four dorsal and three palmar interossei muscles. While all interossei muscles contribute to bending the MCP joints, the dorsal interossei enable us to spread our fingers apart, and the palmar interossei bring our fingers together. The first dorsal interosseous muscle is the largest and is responsible for forming the contour between the thumb and index finger.
The muscles involved in abduction and adduction of the fingers include the abductor pollicis brevis, the abductor digiti minimi, and the adductor pollicis. The abductor pollicis brevis, as mentioned earlier, is responsible for abducting the thumb, moving it away from the index finger. The abductor digiti minimi, a part of the hypothenar muscle group, abducts the little finger, pulling it away from the ring finger. The adductor pollicis, on the other hand, works in the opposite direction, adducting the thumb and bringing it closer to the index finger. This action provides strength and stability during pinching movements.
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Frequently asked questions
No, there are no muscles in the fingers. All the muscles that control finger movement are located in the hand and forearm.
The muscles that control finger movement are the interossei muscles, lumbrical muscles, and the extensor and flexor tendons. The interossei muscles are between the metacarpal bones in your palm and help your fingers move side-to-side. The lumbrical muscles are at the base of your four non-thumb fingers and help you flex your fingers. The extensor tendons help straighten and extend your fingers, while the flexor tendons help you flex and curl your fingers.
Finger extension occurs when you straighten out your hand, such as when releasing an item from your grasp, pointing, or pushing up from a flat surface. Finger flexion occurs when you make a fist or grasp an object.
The interossei and lumbrical muscles help with finger abduction (spreading your fingers apart) and adduction (pulling your fingers back together).
The muscles that move the thumb include the thenar muscle group (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis) and the extensor and flexor tendons. These muscles work together to enable movements like pinching and grasping.
