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The human hand is a complex structure, with more than 30 individual muscles in the hand and forearm working together to achieve a diverse range of movements. The muscles that control finger motion are located in the hand and forearm, with the tendons of these muscles found directly in the hand. The fingers have two long flexors, located on the underside of the forearm, which attach to the phalanges of the fingers. The muscles of the hand can be divided into three main regions: the thenar (lateral or thumb side of the palm), hypothenar (medial or little finger side of the palm), and intermediate (middle of the hand) muscles.
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What You'll Learn
The role of the flexors
The fingers have 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 flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), allowing the thumb to move in opposition, making grasping possible.
The flexor carpi radialis arises adjacent to the pronator teres (an elbow muscle), crosses the elbow and wrist, and attaches to the base of the second hand bone. Its primary role is to bend the wrist, and it can help to move the wrist towards the thumb. The flexor carpi radialis is one of six flexor muscles found in the anterior or palmar side of the forearm. These muscles extend through the wrist via tendons to insert into the bones of the wrist, palm, and fingers. Working together, these muscles flex the hand at the wrist.
The thenar muscle group is found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. It is comprised of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The flexor pollicis brevis bends the thumb toward the small finger. The thenar muscles enable the thumb and the tips of the four fingers to touch each other (opposable thumb). The opponens pollicis moves the thumb across the hand to oppose the other fingers, allowing us to pinch a small object between the thumb and finger to pick it up.
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 flexor digiti minimi flexes the little finger, and the opponens digiti minimi rotates the fifth metacarpal and pulls it anteriorly during opposition with the thumb or while cupping the palm of the hand.
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The role of the extensors
The extensors are muscles located on the back of the forearm, connected to the dorsum of the fingers. They are responsible for straightening out the digits, including the thumb, index finger, and little finger. The extensors are situated within six separate compartments, with the first four located on the dorsum of the inferior side of the radius bone, the fifth between the radius and ulna bones, and the sixth on the dorsum of the inferior side of the ulna bone.
The extensors work in conjunction with the flexors, which are responsible for bending the fingers. The extensors and flexors allow for a wide range of finger movements, such as spreading the fingers apart and pulling them back together. The extensors are essential for various hand functions, including pinching and gripping.
The thumb has two extensors in the forearm, and their tendons form the anatomical snuff box. The index finger and little finger have an extra extensor each, used for pointing, for example. These extra extensors are known as extensor digitorum communis, and they enable the extension of the knuckles (MCP joints) and contribute to the extension of the other finger joints (PIP and DIP).
The extensor hood surrounds the metacarpophalangeal joints (knuckles) and receives tendinous fibres from the interossei and lumbrical muscles. The lumbricals, or lumbrical muscles, are four thin, worm-like muscles that help extend the PIP joints. They attach to the tendons of the extensors of the phalanges, as well as to the flexor digitorum profundus.
The extensors are innervated by the radial nerve, which also innervates the thumb abductor. This means that any injury or issue with the radial nerve can significantly impact the function of the extensors and, consequently, the ability to extend the fingers.
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The thenar muscle group
The thenar muscles are responsible for the fine movements of the thumb, including its abduction and flexion at the metacarpophalangeal (MCP) and carpometacarpal (CMC) joints. The thumb's ability to twist is due to the saddle-shaped carpometacarpal joint. 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 adductor pollicis is a short and broad, fan-shaped muscle of the palm that arises from two muscular heads: the oblique and the transverse. While it is not always considered part of the thenar muscle group, it is often discussed alongside them due to its role in thumb movement. The adductor pollicis muscle produces strong adduction of the thumb at the first carpometacarpal joint, allowing for the opposition of the thumb, which is the combination of flexion, adduction, and medial rotation.
The coordination of the intrinsic muscles of the thumb, including the thenar muscles, facilitates thumb motion and enables precision pinching and power gripping. The median nerve innervates all the thenar muscles.
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The hypothenar muscle group
The hypothenar muscles are intrinsic muscles, located within the hand itself. They are responsible for the fine motor functions of the hand. The hypothenar eminence is a muscular protrusion on the medial side of the palm, at the base of the little finger. The muscles of the hypothenar eminence are innervated by the ulnar nerve.
The palmaris brevis muscle is sometimes considered separate from the hypothenar muscle group. This is because it does not primarily act on the fifth digit. However, it is located in the same region as the hypothenar muscles and is classified as an outstanding superficial muscle of this region. The function of the palmaris brevis muscle is to tighten the palmar aponeurosis and to contribute to the strength of the grip.
The hypothenar muscles are similar to the thenar muscles in both name and organisation. The thenar muscles are found at the base of the thumb, forming the muscle bulk on the thumb side of the hand. The thenar muscle group includes the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. These muscles enable the thumb and the tips of the four fingers to touch each other (opposable thumb) and provide strength and stability when pinching.
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The interossei muscles
The dorsal interossei muscles consist of four short muscles that attach to the adjacent sides of metacarpals 1–4. Their function is to abduct the second, third and fourth digits, as well as to assist in flexion at the metacarpophalangeal (MCP) joints and in extension at the interphalangeal (IP) joints. 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 palmar interossei consist of four muscles that attach to the first, second, fourth and fifth fingers. The third finger does not contain a palmar interosseous muscle. The palmar interossei are strong adductors of the fingers, but they also contribute to flexion and extension of the second, fourth and fifth fingers. The first palmar interosseous pulls the index finger medially, while the second and third pull the ring and little fingers laterally. Functionally, the palmar interossei are antagonists to the dorsal interossei in the MCP joint.
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Frequently asked questions
The muscles that control finger movement are located in the forearm and hand. There are over 30 muscles in the hand and forearm that work together to move the fingers. The muscles in the forearm that control finger movement are called extrinsic muscles. The muscles in the hand that control finger movement are called intrinsic muscles.
The muscles in the forearm that control finger movement are the flexors and extensors. The extensors are located on the back of the forearm and are connected to the dorsum of the fingers. The flexors are located on the underside of the forearm and are connected to the phalanges of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The extensors in the forearm are connected to the extensor hood, which surrounds the metacarpophalangeal joints.
The muscles in the hand that control finger movement are the thenar, hypothenar, interossei, and lumbrical muscles. The thenar muscles are at the base of the thumb and include the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis. The hypothenar muscles are at the base of the little finger and include the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi. The interossei muscles include four dorsal and three palmar interossei muscles, which allow us to spread our fingers away from each other and pull them back together. The lumbricals are four thin, worm-like muscles that help to bend the metacarpophalangeal joints and extend the fingers.
