Logan Steele
The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. The muscles of the hand are responsible for its movement and can be divided into two groups: extrinsic and intrinsic muscles. The extrinsic muscles are located in the forearm and control crude movements, while the intrinsic muscles are located within the hand itself and are responsible for fine motor functions. Each finger has six muscles controlling its movement: three extrinsic and three intrinsic muscles. The movement of the fingers is also supported by various soft tissues, including articular cartilage, ligaments, and tendons. The nerves of the hand carry electrical signals from the brain to these muscles, enabling movement and the senses of touch, pain, and temperature.
| Characteristics | Values |
|---|---|
| Muscle groups | Extrinsic, Intrinsic |
| Muscle controlling finger movement | Opponens pollicis |
| Location of extrinsic muscles | Forearm or elbow |
| Function of extrinsic muscles | Control the movement of the wrist and hand, Responsible for gross hand movements |
| Location of intrinsic muscles | Within the hand itself |
| Function of intrinsic muscles | Responsible for fine motor functions of the hand |
| Muscle controlling thumb movement | Thenar |
| Muscle controlling movement of the little finger | Hypothenar |
| Muscle controlling finger side-to-side movement | Interossei |
| Muscle helping to flex fingers | Lumbrical |
| Muscle allowing fingers to straighten | Lumbrical |
| Muscle providing power for pinching | Adductor pollicis |
| Muscle allowing the small finger to bend at the MCP joint | Flexor digiti minimi |
| Muscle allowing the small finger to pull away from the ring finger | Abductor digiti minimi |
| Muscle allowing us to cup our hands | Opponens digiti minimi |
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What You'll Learn
Intrinsic and extrinsic muscles
The skeletal muscles of the hand are responsible for the movement of the hand and fingers. These muscles are divided into two groups: extrinsic and intrinsic muscles. The extrinsic muscles are so-called because their muscle bellies originate in the forearm, specifically in the anterior and posterior compartments. They control crude movements and produce a forceful grip. The intrinsic muscles, on the other hand, are located within the hand itself and are responsible for the fine motor functions of the hand. They are smaller muscles located within the various hand osseofascial compartments within the wrist and phalanges. The intrinsics are important for various hand functions, such as pinch and grip strength. Understanding the intrinsic hand muscle groups is crucial, as denervation and loss of function may lead to pronounced deficits in hand function.
The hypothenar muscles form a muscular protrusion on the medial side of the palm, at the base of the little finger. They are similar to the thenar muscles in both name and organisation. 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 by bringing the small finger towards the thumb.
The thenar muscles are three short muscles located at the base of the thumb. The muscle bellies produce a bulge, known as the thenar eminence. They are responsible for the fine movements of the thumb. The thenar muscle group is formed by 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 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.
The interossei muscles are between the metacarpal bones in the palm. There are four dorsal and three palmar interossei muscles. While all interossei bend the MCP joints, the dorsal interossei allow us to spread our fingers away from each other, and the palmar interossei 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.
The lumbrical muscles are at the base of the four non-thumb fingers. They are crucial to finger movement, linking the extensor tendons to the flexor tendons. There are four lumbricals in the hand, each associated with a finger. They help to flex the fingers and allow them to straighten.
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Interossei muscles
The interossei muscles are intrinsic hand muscles situated between the metacarpal bones in the palm. They are responsible for helping the fingers move side-to-side. There are eight interossei muscles in total, consisting of four dorsal and three palmar interossei muscles. The interossei muscles are considered voluntary muscles.
The palmar interossei facilitate finger adduction, pulling the fingers together. They adduct the 1st, 2nd, 4th, and 5th digits about an axis through the midline of the 3rd digit. Adduction occurs at the MCP joints. Additionally, the palmar interossei contribute to flexion at the MCP joints and extension at the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints of their respective digits. The first palmar interosseous is frequently considered rudimentary, with many anatomical sources classifying it as part of either the adductor pollicis or the flexor pollicis brevis. The second palmar interosseous originates from the medial surface of the base of the 2nd metacarpal and inserts into the medial portion of the extensor hood and base of the proximal 1st phalanx. The third and fourth palmar interossei originate from the lateral aspects of the 4th and 5th metacarpals and insert into the lateral portions of their respective extensor hoods and the bases of their corresponding proximal phalanges.
The dorsal interossei enable finger abduction, allowing us to spread our fingers away from each other. They are associated with the abduction of the 2nd, 3rd, and 4th fingers, and their tendons run dorsally to the deep transverse metacarpal ligament. The dorsal interossei are the most dorsally located intrinsic hand muscles. 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. The fourth dorsal interosseous originates from the lateral aspect of the 4th metacarpal and the medial side of the 5th metacarpal. This muscle inserts into the lateral base of the 4th proximal phalanx and the extensor hood of the 4th digit.
Both the palmar and dorsal interossei contribute to metacarpophalangeal (MCP) joint flexion and interphalangeal joint extension. All interossei receive innervation from the deep branch of the ulnar nerve. Consequently, ulnar nerve injury may significantly impair intrinsic hand functions, particularly finger abduction and adduction.
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Lumbrical muscles
The lumbrical muscles are a set of four intrinsic hand muscles attached to the flexor digitorum profundus (FDP) tendons proximally and the digits' extensor expansions distally. They are cylindrical and worm-like, resembling earthworms. They are located deep in the palm and are essential for the fingers' precision grip and fine motor control. Each finger is attached to two lumbricals, except for the thumb, which is associated with only the first lumbrical muscle.
The lumbricals flex the metacarpophalangeal (MCP) joints and extend the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints. By coordinating with other hand muscles, the lumbricals help control the delicate movements of the fingers. The actions of these muscles are essential for gripping objects, typing, and performing various dexterous hand movements.
The first and second lumbricals (the most radial two) are innervated by the median nerve. The third and fourth lumbricals (the most ulnar two) are innervated by the deep branch of the ulnar nerve. This is the most common innervation pattern of the lumbricals, occurring in 50-60% of individuals. However, 20-30% of individuals have the median nerve innervating only the first lumbrical, while the rest have the median nerve innervating the lateral three lumbricals.
The lumbrical muscles are sometimes damaged in crush injuries to the hand. Following these injuries, adhesions may occur between the lumbrical muscle and the interosseous muscle. This deformity causes the patient to experience intermetacarpal pain when making a fist. It can typically be treated by releasing the involved muscles. The lumbrical muscles have also been shown to be relevant in carpal tunnel syndrome.
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Thenar and hypothenar muscles
The human hand is a complex structure of bones, muscles, nerves, tendons, ligaments, and blood vessels. The skeletal muscles of the hand are responsible for the movement of the hand and fingers. These muscles are divided into two groups: the extrinsic and intrinsic muscles. The intrinsic muscles of the hand are located within the hand itself and are responsible for fine motor functions. They include the thenar and hypothenar muscles, which are responsible for the movement of the thumb and little finger, respectively.
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 made up of three muscles: the abductor pollicis brevis, the flexor pollicis brevis, and the opponens pollicis. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two. It pulls the thumb away from the fingers, allowing us to grasp objects. The abductor pollicis brevis pulls the thumb away from the index finger, while the flexor pollicis brevis bends the thumb toward 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 little finger side of the hand. The abductor digiti minimi is the most superficial of the hypothenar muscles and causes the little finger to abduct away from the hand. The flexor digiti minimi brevis flexes the little finger at the metacarpophalangeal joint. The opponens digiti minimi moves the little finger to allow the opposition of the hand, where the pad of the thumb touches the pad of the little finger.
In addition to their role in finger movement, the thenar and hypothenar muscles also contribute to the overall structure and stability of the hand. The thenar eminence, or the fleshy part at the base of the thumb, is formed by the thenar muscles. Similarly, the hypothenar eminence, the fleshy part at the base of the little finger, is formed by the hypothenar muscles. These eminences provide stability and help with fine motor movements of the hand.
Injuries to the thenar and hypothenar muscles can result in significant hand dysfunction. Loss of these muscles can lead to palmar atrophy and weakness in thumb and little finger abduction, flexion, and opposition. Physiotherapy can aid in regaining hand function, and in some cases, surgery may be required. Understanding the anatomy of these muscle groups is crucial for safe and effective treatment approaches.
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Flexor and extensor tendons
The human hand and wrist are a complex network of bones, muscles, nerves, tendons, and ligaments. The muscles that move the fingers and thumb are located in the forearm and hand.
Tendons are fibrous cords, similar to ropes, and are made of collagen. They have blood vessels and cells to maintain tendon health and repair injured tendons. Tendons link muscles to bones, and when muscles contract, tendons pull through the attachments to bones and cause a joint to move.
The hand and wrist have two groups of tendons: flexor and extensor tendons. Flexor tendons help to flex and curl the fingers, hand, and wrist, allowing you to bend your fingers and thumb to grasp an object or make a fist. Extensor tendons help to extend and straighten the fingers, hand, and wrist.
Flexor tendons are divided into five zones based on their anatomical location. The FDS and FDP are the two flexor tendons within digits 2-5. The FDS splits at the MCP joint to allow the FDP to pass through and insert distally, enabling coordinated movement between superficial and deep tendons. The FDP tendon helps bend the index, middle, ring, and small fingers at the fingertip joint. The FDS helps bend the same fingers at the middle finger joint. The FPL tendon bends the thumb.
Extensor tendons work with the muscles that attach to the back of the fingers to straighten the finger joints. The EIP tendon straightens the index finger. The EPL straightens the most distal joint of the thumb. The APL tendon runs on the radial side of the wrist and helps pull the thumb away from the rest of the hand.
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Frequently asked questions
The muscles that control finger movement are called intrinsic and extrinsic muscles. Intrinsic muscles are small muscles that originate in the wrist and hand and are responsible for fine motor movement. Extrinsic muscles, on the other hand, originate in the forearm or elbow and control the movement of the wrist and hand, allowing for gross hand movements.
Intrinsic muscles include the thenar muscle group, hypothenar muscle group, interossei muscles, lumbrical muscles, and adductor pollicis. The thenar muscle group is found at the base of the thumb and is responsible for its fine movements. The hypothenar muscle group, on the other hand, forms a muscular protrusion on the medial side of the palm, at the base of the little finger. The interossei muscles help the fingers move side-to-side, while the lumbrical muscles help flex the fingers.
Each finger has six muscles controlling its movement: three extrinsic and three intrinsic muscles. The index and little fingers each have an extra extrinsic extensor. The flexor digitorum profundus is an extrinsic muscle that arises from the ulna and interosseous membrane. Four tendons emerge from this muscle and insert into the tips of the index, middle, ring, and small fingers, allowing them to bend.
