Victor Forge
The human hand is a complex structure, with over 30 individual muscles in the hand and forearm working together to achieve a diverse range of movements. These muscles are innervated by the radial, median, and ulnar nerves, and can be classified as intrinsic or extrinsic. Intrinsic muscles are located within the hand itself and are responsible for fine motor functions, while extrinsic muscles are found near the outside of the hand and in the forearm, providing strength and dexterity. The hand's muscles work with tendons and ligaments to allow for flexion, extension, adduction, and abduction, resulting in the flexibility, precise control, and gripping strength necessary for various activities.
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What You'll Learn
Thenar muscles control the thumb
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which work together to help us move our hands and fingers.
The thenar muscles are an intrinsic group of muscles that control the thumb. The word 'thenar' comes from the Ancient Greek 'θέναρ' ('thenar'), meaning 'palm of the hand'. The thenar eminence is the mound formed at the base of the thumb in the palm of the hand. The thenar muscles are considered to be part of the thenar eminence.
The thenar muscles include the abductor pollicis brevis, which abducts the thumb. This is the most superficial of the thenar group. The abductor pollicis brevis originates from the tubercles of the scaphoid and trapezium bones, as well as the flexor retinaculum. The muscle fibres extend laterally and distally, ending in a tendon that inserts onto the lateral aspect of the base of the proximal phalanx. The abductor pollicis brevis receives its innervation via the recurrent (thenar) branch of the median nerve. Its blood supply is provided mainly by the superficial palmar branch of the radial artery. The prime function of this muscle is the abduction of the thumb at the first carpometacarpal joint.
The thenar group also includes the flexor pollicis brevis, which lies next to the abductor pollicis brevis and flexes the thumb, curling it up in the palm. The flexor pollicis brevis arises by two muscle heads (superficial and deep) which are separated by the tendon of flexor pollicis longus. The superficial head originates from the flexor retinaculum and the tubercle of the trapezium bone, while the deep head originates from the trapezoid and capitate bones. The two heads of the flexor pollicis brevis muscle differ in innervation. The superficial head receives its innervation via the recurrent branch of the median nerve, while the deep head is innervated by the deep branch of the ulnar nerve. The blood supply for this muscle is derived from the radial artery. The prime function of the flexor pollicis brevis muscle is to produce flexion of the thumb at the metacarpophalangeal and carpometacarpal joints.
Another muscle in the thenar group is the opponens pollicis, which lies deep to the abductor pollicis brevis. As its name suggests, it opposes the thumb, bringing it against the fingers. The opponens pollicis is a short muscle that originates from the tubercle of the trapezium bone and flexor retinaculum. The muscle fibres then run distally to insert onto the lateral aspect of the first metacarpal bone. The opponens pollicis muscle receives its innervation via the recurrent branch of the median nerve, and its blood supply via the superficial palmar branch of the radial artery. The prime function of the opponens pollicis is to produce the opposition of the thumb in the first carpometacarpal joint.
The adductor pollicis is sometimes described together with the thenar muscles when discussing the movements of the thumb, although it is not part of the thenar muscle group. It is a short and broad, fan-shaped muscle of the palm and arises by the two muscular heads: oblique and transverse. The transverse head originates from the palmar base of the third metacarpal bone, while the oblique head arises from the capitate bone and palmar bases of the second and third metacarpal bones. From their origins, the muscle heads run laterally, converging into a single muscle belly that inserts onto the medial base of the proximal phalanx. The adductor pollicis muscle receives its innervation via the deep branch of the ulnar nerve, and its blood supply from the deep palmar arch. The prime function of the adductor pollicis muscle is to produce strong adduction of the thumb at the first carpometacarpal joint.
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Hypothenar muscles control the area opposite the thumb
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. The movement of opposition, which involves moving the thumb in opposition to the fingers, played an important role in human evolution. This movement is made possible by the muscles that attach to the thumb, including the hypothenar muscles.
The hypothenar muscles are located on the outer edges of the palm, lining the outside of the pinkie finger. They are the three short muscles of the medial (ulnar) palmar compartment of the hand. From superficial to deep, the hypothenar muscles are: abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi muscles. A fourth muscle, the palmaris brevis, is also located in this region but is not part of the hypothenar muscle group.
The hypothenar muscles form the hypothenar eminence, a muscular protrusion on the medial side of the palm at the base of the little finger. These muscles are similar to the thenar muscles, which control the thumb, in both name and organisation. The hypothenar eminence is one of two "fleshy" mounds that can be observed on the palmar side of the hand, the other being the thenar eminence.
The hypothenar muscles contribute to the variety of movements of the little finger, including flexion, abduction, lateral rotation, and opposition. The abductor digiti minimi, the most superficial muscle of the hypothenar group, abducts the little finger. The flexor digiti minimi brevis flexes the fifth digit at the metacarpophalangeal joint and participates in the lateral rotation and opposition of the little finger. The opponens digiti minimi rotates the metacarpal of the little finger towards the palm, producing opposition.
The hypothenar muscles are innervated by the ulnar nerve, except for the palmaris brevis, which is supplied by the superficial branch of the ulnar nerve. The blood supply for the hypothenar eminence comes mainly from the ulnar artery via the superficial palmar arch.
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Interossei muscles help fingers move side-to-side
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which work together to help you move your fingers and control objects.
The interossei muscles are among the intrinsic muscles of the hand, consisting of four palmar and four dorsal muscles. They are located between the metacarpal bones in the palm. The dorsal interossei muscles consist of four short muscles that attach to the adjacent sides of metacarpals 1-4. The palmar interossei are unipennate muscles of the palmar surface of the hand. They are smaller than the dorsal interossei and are situated on the palmar surface of the hand in between the metacarpal bones.
The interossei muscles contribute to abduction and adduction of the fingers, which is the movement of the fingers towards or away from the middle finger. The dorsal interossei 1-2 pull the digits 2-3 laterally (radial abduction), while the dorsal interossei 3-4 move the digits 3-4 medially (ulnar abduction). The palmar interossei, on the other hand, are strong adductors of the fingers, pulling the fingers towards the midline. Specifically, the 1st palmar interosseous pulls the index finger medially, whereas the 2nd and 3rd pull the ring and little fingers laterally.
In addition to their role in finger abduction and adduction, the interossei muscles also contribute to finger flexion and extension. The dorsal interossei assist in flexion of the metacarpophalangeal (MCP) joints and extension at the interphalangeal (IP) joints. The palmar interossei contribute to flexion at the MCP joint and extension at the interphalangeal joints of the 2nd, 4th, and 5th fingers.
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Lumbrical muscles help flex the fingers
The human hand is a complex network of bones, muscles, nerves, connective tissue, and blood vessels. There are 34 muscles in each hand, which work together to help us move our hands and fingers. These muscles can be categorised into groups, including thenar muscles, hypothenar muscles, interossei muscles, and lumbrical muscles.
Lumbrical muscles are intrinsic muscles of the hand that help flex the metacarpophalangeal joints and extend the interphalangeal joints. They are four small worm-like muscles on each hand, located at the base of the four non-thumb fingers. Lumbricals are unusual in that they do not attach to bone. Instead, they attach proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions, making their attachment points quite mobile.
The lumbricals allow for two different actions: flexion at the metacarpophalangeal joints and extension in both the proximal and distal interphalangeal joints. These combined movements play a role in complex hand movements, such as holding a pen, and contribute to the hand's general dexterity. The tendons cross the metacarpophalangeal joints on the palmar side but distally insert at the dorsal side of the finger, allowing for these opposite actions.
The median nerve innervates the first and second lumbricals, while the third and fourth lumbricals are innervated by the deep branch of the ulnar nerve. This is the usual innervation pattern, occurring in 60% of individuals. However, different innervation patterns, such as 1:3 and 3:1 median-to-ulnar ratios, can also be found in a minority of cases.
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Flexion and extension muscles move the wrist up and down
The human hand is a complex network of bones, muscles, nerves, tendons, ligaments, and blood vessels. The wrist acts as a pivot point, allowing the hand to move in almost any direction.
Flexion and extension are the terms used to describe the movement of the wrist up and down. Flexion is the movement of the wrist down, towards the palm, while extension is the movement of the wrist up, away from the palm.
The flexor carpi radialis, which arises adjacent to the pronator teres (an elbow muscle), is one of the prime movers of flexion. It crosses the elbow and wrist and attaches to the base of the second hand bone. The flexor carpi ulnaris is another prime mover of flexion, working with the extensor carpi ulnaris to pull the wrist towards the ulna. The extensor carpi radialis longus and extensor carpi radialis brevis are prime movers of extension. The extensor carpi radialis longus arises just above the ECRB muscle on the outside of the elbow and attaches to the second hand bone. The extensor carpi ulnaris arises from the lateral epicondyle, an elbow bone, and attaches to the fifth hand bone after passing over the ulna bone.
These muscles are controlled by the radial, median, and ulnar nerves. The radial nerve innervates the finger extensors, the median nerve innervates the flexors of the wrist, and the ulnar nerve innervates the remaining intrinsic muscles of the hand.
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Frequently asked questions
There are 34 muscles in each hand that work together to move the hand and fingers. These muscles are innervated by the radial, median, and ulnar nerves.
The hand muscles can be classified as intrinsic (within the hand itself) and extrinsic (near the outside of the hand and in the forearm). Intrinsic muscles are responsible for fine motor functions.
Intrinsic hand muscles include the adductor pollicis, hypothenar muscles, thenar muscles, interossei muscles, and lumbrical muscles.
The interossei muscles are located between the metacarpal bones in the palm. They help the fingers move side-to-side and assist with finger abduction and adduction.
Extrinsic hand muscles include the flexor carpi radialis, palmaris longus, and extensor carpi radialis longus. These muscles help with movements like bending the wrist, moving the wrist towards the thumb, and straightening and stabilising the wrist.
