Dominic Stone
The muscles in the human body are groups of cells that can contract and relax. The intrinsic muscles of the hand are responsible for fine motor functions. Finger abduction is enabled by the dorsal interossei muscles, which are located between the metacarpal bones of the hand. Each finger is provided with two interossei muscles, except for the little finger, where the abductor digiti minimi muscle replaces one of the dorsal interossei. The interossei muscles also assist in flexion at the MCP joints and extension at the IP joints.
| Characteristics | Values |
|---|---|
| Muscle responsible for finger abduction | Dorsal interossei |
| Location of dorsal interossei | Between the metacarpal bones of the hand |
| Number of dorsal interossei muscles | 4 |
| Innervation | Ulnar nerve |
| Function | Abduction of the index, middle, and ring fingers |
| Location of abductor digiti minimi | Lateral to the flexor digiti minimi brevis |
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What You'll Learn
- The abductor digiti minimi muscle allows the small finger to pull away from the ring finger
- The flexor digiti minimi brevis flexes the metacarpophalangeal joint of the little finger
- The interossei muscles are located between the metacarpal bones
- The palmar interossei muscles adduct the thumb, index, ring and little fingers
- The lumbricals of the hand are innervated by the median and ulnar nerves
The abductor digiti minimi muscle allows the small finger to pull away from the ring finger
The abductor digiti minimi muscle is one of the intrinsic muscles of the hand, which are responsible for the fine motor functions of the hand. This muscle takes the place of one of the dorsal interossei in the little finger. The abductor digiti minimi muscle is effectively the fifth dorsal interosseus or the dorsal interosseus of the little finger.
The dorsal interossei are the most dorsally located intrinsic hand muscles. They are the primary abductors of the second, third, and fourth digits at the MCP joints. The MCP joints are the knuckles, and the dorsal interossei also help to bend these joints and extend the interphalangeal (IP) joints. The IP joints are the joints between the bones of the fingers.
The palmar interossei, on the other hand, facilitate adduction of the fingers. Both the palmar and dorsal interossei receive innervation from the deep branch of the ulnar nerve. Consequently, injury to the ulnar nerve may lead to weakness or atrophy of the interossei, resulting in impaired finger abduction and adduction.
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The flexor digiti minimi brevis flexes the metacarpophalangeal joint of the little finger
The flexor digiti minimi brevis is a hypothenar muscle in the hand that flexes the little finger at the metacarpophalangeal joint. The name of this muscle is Latin for the 'short flexor of the little finger'. The brevis is used to differentiate it from a longus muscle with the same name. The flexor digiti minimi longus is not found in the typical human but is a rare anatomical variation.
The flexor digiti minimi brevis arises from the hamulus of the hamate bone and the palmar surface of the flexor retinaculum of the hand. It is inserted into the medial side of the base of the proximal phalanx of the little finger. It is separated from the abductor digiti minimi, at its origin, by the deep branches of the ulnar artery and the ulnar nerve. The flexor digiti minimi brevis is sometimes not present in the hand. In these cases, the abductor digiti minimi is usually larger than normal.
The flexor digiti minimi brevis is one of three muscles in the hypothenar muscle group. These three muscles form the fleshy mass at the base of the little finger and are solely concerned with the movement of the digit. The muscle is located on the ulnar side of the palm, creating the hypothenar eminence with the abductor digiti minimi and opponens digiti minimi muscles.
The flexor digiti minimi brevis also participates in the lateral rotation and opposition of the little finger. The ulnar nerve can become compressed when it travels between the hook of the hamate and the pisiform bone (Guyon's canal). Atrophy, numbness, tingling, and discomfort in the hypothenar eminence, as well as the fourth and fifth fingers, are all symptoms of ulnar nerve damage.
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The interossei muscles are located between the metacarpal bones
The interossei muscles are intrinsic hand muscles located between the metacarpal bones. They are responsible for the fine motor functions of the hand and are considered voluntary muscles. The interossei muscles can be divided into two groups: the palmar interossei and the dorsal interossei. Each group comprises four muscles. The palmar interossei facilitate finger adduction, while the dorsal interossei enable abduction.
The palmar interossei muscles adduct the digits towards the third digit (towards the axial line) and are unipennate. They originate from the metacarpals of the respective digit to which they are associated. 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. Blood supply to the palmar interossei comes from the palmar metacarpal arteries and drains into the palmar metacarpal veins.
The dorsal interossei muscles are the most dorsally located intrinsic hand muscles. They are bipennate muscles and serve as the primary abductors of the second, third, and fourth digits at the MCP joints. The first dorsal interosseous originates from the adjacent surfaces of the first and second metacarpals and inserts into the lateral base of the second proximal phalanx and the extensor hood. The second dorsal interosseous originates from the medial aspect of the second metacarpal and the lateral aspect of the third metacarpal. The third dorsal interosseous originates from the medial surface of the third metacarpal and the lateral surface of the fourth metacarpal, inserting into the medial base of the third proximal phalanx. The middle digit has two dorsal interossei insert onto it, while the first digit (thumb) and the fifth digit (little finger) have none.
The interossei muscles also assist the lumbricals in flexion at the MCP joints and extension at the IP joints. 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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The palmar interossei muscles adduct the thumb, index, ring and little fingers
The interossei muscles are located between the metacarpal bones of the hand. They can be divided into two groups: dorsal and palmar. The palmar interossei muscles adduct the thumb, index, ring and little fingers.
The palmar interossei are four muscles, one on the thumb that is occasionally missing, and three small, unipennate, central muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand. All palmar interossei originate along the shaft of the metacarpal bone of the digit on which they act. They are inserted into the base of the proximal phalanx and the extensor expansion of the extensor digitorum of the same digit. The first palmar interosseous is located at the thumb's medial side. Passing between the first dorsal interosseous and the oblique head of adductor pollicis, it is inserted on the base of the thumb's proximal phalanx together with adductor pollicis.
The second palmar interosseous originates at the medial surface of the base of the second metacarpal. The third and fourth palmar interossei originate at the lateral aspect of the fourth and fifth metacarpals. The tendons of these three muscles pass posterior to the deep transverse ligament before being inserted onto the extensor expansion. The pollical palmar interosseous muscle (PPIM) is present in more than 80% of individuals and was first described in 1858. Its presence has been verified by numerous anatomists since, but others have either failed to mention it or considered it part of either the adductor pollicis or flexor pollicis brevis.
The palmar interossei, together with the dorsal interossei and the lumbricals, are active components of the finger's extensor mechanism. Fibers from some of the interossei contribute directly to the extensor hoods that wrap around the proximal phalanges, while other fibers may contribute to the central tendon and lateral bands of the mechanism. All three intrinsic groups of muscles pass palmar to the axis of the metacarpophalangeal joints, and therefore contribute to flexion there. Extension at the interphalangeal joints cannot be produced by the extensor digitorum alone, but active contraction of one of the three aforementioned intrinsic groups will because of their direct contribution to the extensor mechanism.
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The lumbricals of the hand are innervated by the median and ulnar nerves
The lumbricals are a group of four muscles in the hand, each associated with a finger. They are crucial to finger movement, allowing the fingers to straighten and linking the extensor tendons to the flexor tendons. The name 'lumbrical' is derived from the Greek word for earthworm.
The lateral two lumbricals, associated with the index and middle fingers, are innervated by the median nerve. The median nerve travels along the inside of the arm near the brachial artery and supplies almost all the flexor muscles and all the pronator muscles of the forearm with nerves. It allows the wrist and fingers to bend and pronates the forearm (rotating the hand to face palm down). The median nerve is the most well-known nerve of the brachial plexus because it can be compressed as it crosses the wrist, causing carpal tunnel syndrome.
The medial two lumbricals, associated with the little and ring fingers, are innervated by the ulnar nerve. The ulnar nerve is very close to the skin at the elbow and can be compressed when it crosses the elbow, causing numbness and tingling in the small and ring fingers, and weakness of the hand, known as cubital tunnel syndrome. The ulnar nerve then travels on the inside of the forearm, powering the muscles that bend the tips of the small and ring fingers and one of the muscles that bends the wrist. The nerve powers almost all of the small muscles in the hand, including the hypothenar muscles, the palmar and dorsal interossei muscles, the adductor pollicus, and the deep head of the flexor pollicus brevis.
The interossei muscles are located between the metacarpal bones of the hand and can be divided into two groups: dorsal and palmar. They assist the lumbricals in flexion at the MCP joints and extension at the interphalangeal (IP) joints. The dorsal interossei abduct the index, middle, and ring fingers, while the palmar interossei adduct the digits.
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Frequently asked questions
The interossei muscles are located between the metacarpal bones of the hand and are divided into two groups: palmar and dorsal interossei. The dorsal interossei are the primary abductors of the fingers.
The dorsal interossei abduct the index, middle, and ring fingers. They also contribute to MCP joint flexion and extension at the PIP and DIP joints.
The palmar interossei facilitate finger adduction and contribute to MCP joint flexion and extension at the IP joints.
The interossei muscles receive innervation from the deep branch of the ulnar nerve. Injury to this nerve may lead to weakness or atrophy of the interossei, resulting in impaired finger abduction and adduction.
