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The muscles in the human body are groups of cells that have the ability to contract and relax. The intrinsic muscles of the hand are located within the hand itself and are responsible for the fine motor functions of the hand. The palmar interossei muscles are a group of three or four muscles that are responsible for adducting the fingers, that is, moving them towards the middle finger. The adductor pollicis is another muscle that is responsible for adducting the thumb.
| Characteristics | Values |
|---|---|
| Name | Palmar interossei muscles |
| Type | Intrinsic muscles of the hand |
| Number of Muscles | 4 (the first is rudimentary) |
| Origin | Medial or lateral surface of a metacarpal |
| Insertion | Extensor hood and proximal phalanx of the same finger |
| Action | Adduction of the digits, flexion at the metacarpophalangeal joints, and extension at the interphalangeal joints |
| Innervation | Ulnar nerve |
| Blood Supply | Branches of the deep palmar arch, princeps pollicis artery, radialis indicis artery, palmar metacarpal arteries, proximal and distal perforating arteries, and common and proper palmar arteries |
| Mnemonic | PAD and DAB |
| Adduction of the Thumb | Adductor pollicis |
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What You'll Learn
Palmar interossei muscles adduct fingers
The palmar interossei muscles are three or four short, unipennate muscles on the palmar surface of the hand. They are part of the intrinsic muscles of the hand, which are responsible for the fine motor functions of the hand. The palmar interossei muscles are smaller than the dorsal interossei and are situated on the palmar surface of the hand in between the metacarpal bones.
The main function of the palmar interossei muscles is to adduct the fingers in a longitudinal axis, which means the movement of the fingers towards the middle finger. Specifically, the first palmar interosseous pulls the index finger medially, while the second and third pull the ring and little fingers laterally. The middle finger cannot be adducted.
The palmar interossei muscles also contribute to flexion at the metacarpophalangeal joints and extension at the interphalangeal joints. The reference axis through which abduction and adduction occur is the long axis of the third phalanx (middle finger).
A positive Wartenberg's sign test will produce abduction of the fifth finger relative to all other digits, implying weakness of the third palmar interosseous muscle and fourth lumbrical.
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Adductor pollicis muscle
The adductor pollicis muscle is a fleshy, flat, triangular, and fan-shaped muscle in the hand. It is an intrinsic muscle, which means it is located within the hand itself. It is the only muscle in the adductor compartment of the hand. The adductor pollicis muscle has two heads: the transverse head and the oblique head. The transverse head is Latin for adductor transversus pollicis, while the oblique head is Latin for adductor obliquus pollicis. The muscle is innervated by the deep branch of the ulnar nerve (C8-T1).
The adductor pollicis muscle is responsible for the adduction of the thumb, which is the movement of the thumb towards the index finger from an abducted position. This action is essential for functions that require pinching and gripping. The muscle also aids in the later stages of opposition of the thumb. The thumb is one of the most important parts of the hand due to its versatility in movement compared to the other digits. The adductor pollicis muscle is one of the many muscles that contribute to the thumb's movement.
The transverse head of the adductor pollicis muscle is deeply seated and triangular in shape. It arises from the third metacarpal bone, specifically from the lower two-thirds of the palmar surface. The oblique head, on the other hand, originates from the capitate bone and the palmar bases of the second and third metacarpals. The two heads then converge into a single muscle belly as the fibres run laterally towards the thumb. The muscle ends in a tendon that inserts into the base of the first proximal phalanx.
The adductor pollicis muscle is an important anatomical landmark for the radial artery. The radial artery passes between the two heads of the muscle as it enters the hand and forms the deep palmar arch. The strength of the adductor pollicis muscle can be tested by pushing the thumb against the index finger while attempting to pull them apart. This test assesses the strength of adduction and ensures the ulnar nerve is intact.
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Interossei muscles
The interossei muscles are a group of intrinsic hand muscles situated between the metacarpals. They are categorised into two groups: palmar interossei and dorsal interossei, each comprising four muscles. The palmar interossei facilitate finger adduction, while the dorsal interossei enable abduction.
The palmar interossei muscles are unipennate and more volar in relation to the dorsal interossei. There are four muscles in this group, however, the first is often considered rudimentary and part of either the adductor pollicis or the flexor pollicis brevis. The adductor pollicis is a large triangular muscle with two heads. One head originates from metacarpal III, while the other originates from the capitate and adjacent areas of metacarpals II and III. Both attach to the base of the proximal phalanx of the thumb. The adductor pollicis is responsible for providing power for pinching and filling the first web space between the thumb and index finger.
The remaining three palmar interossei muscles adduct the index, ring, and little fingers along the long axis of the middle finger. The middle finger cannot be adducted. The tendons of the palmar interossei pass deep to the transverse metacarpal ligament. The first palmar interosseous lies anterior to the first dorsal interosseous.
The dorsal interossei muscles are bipennate and are responsible for abducting the digits away from the third digit (away from the axial line). The first and fifth digits do not have interossei musculature and have their own abductor muscles in the thenar and hypothenar eminence. The dorsal interossei attach to the extensor expansion (extensor hood) of the digits, assisting in flexion and extension of the metacarpophalangeal and interphalangeal joints.
Both the palmar and dorsal interossei contribute to metacarpophalangeal (MCP) joint flexion and interphalangeal joint extension. All interossei muscles receive innervation from the deep branch of the ulnar nerve. Consequently, an injury to the ulnar nerve may significantly impair intrinsic hand functions, particularly finger abduction and adduction.
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Intrinsic muscles of the hand
The intrinsic muscles of the hand are located within the hand itself and are responsible for the fine motor functions of the hand. The development of these muscles begins in the fourth week of embryonic development, when the upper extremity first becomes visible as a lateral projection, or limb bud.
The muscles of the hand are innervated by the radial, median, and ulnar nerves. The median nerve innervates the flexors of the wrist and digits, the abductors and opponens of the thumb, and the first and second lumbricals. The median nerve also innervates all the thenar muscles, which are three short muscles located at the base of the thumb and responsible for its fine movements. The opponens pollicis is the largest of the thenar muscles and lies underneath the other two.
The ulnar nerve innervates the remaining intrinsic muscles of the hand, including the hypothenar muscles, which form a protrusion on the medial side of the palm at the base of the little finger. The abductor digiti minimi is the most superficial of the hypothenar muscle group and abducts the little finger. The flexor digiti minimi brevis lies laterally to the abductor digiti minimi and flexes the metacarpophalangeal joint of the little finger.
The lumbricals 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. The lateral two lumbricals (of the index and middle fingers) are innervated by the median nerve, while the medial two lumbricals (of the little and ring fingers) are innervated by the ulnar nerve. The interossei muscles, located between the metacarpal bones of the hand, assist the lumbricals in flexion and extension.
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Ulnar nerve
The ulnar nerve is one of the five terminal branches of the brachial plexus, which arises from the medial cord. The nerve originates from the C8-T1 nerve roots and occasionally carries C7 fibres from the lateral cord. The ulnar nerve is the largest nerve in the human body that is not protected by muscle or bone, making it susceptible to injury.
The nerve runs near the ulna, one of the two long bones in the forearm, and is directly connected to the little finger and the adjacent half of the ring finger. It innervates the palmar aspect of these fingers, including the front and back of the fingertips, and potentially as far back as the nail bed. The ulnar nerve is responsible for controlling movement and sensation in the hand, ring finger, and little finger. It also helps with gripping and fine motor skills, such as writing.
The ulnar nerve courses along the medial arm and forearm, passing into the wrist, hand, and fingers. It provides motor innervation to part of the forearm and most of the hand, supplying sensory cutaneous innervation to the medial forearm, medial wrist, and medial one and a half digits. The nerve sends motor innervation to the flexor carpi ulnaris and flexor digitorum profundus in the forearm, and hypothenar muscles in the hand, such as the opponens digiti minimi, abductor digiti minimi, and flexor digiti minimi brevis.
The ulnar nerve has several branches, including the palmar cutaneous (nerve of Henle) and the dorsal cutaneous branch, which bifurcates into radial and ulnar branches providing sensation to the dorsal hand. The nerve innervates the flexor muscles of the forearm and the intrinsic muscles of the hand, such as the palmaris brevis, lumbricals, hypothenar, and interossei muscles. The superficial branch of the ulnar nerve innervates the palmaris brevis muscle, the sensory function of the hypothenar muscles, the fourth common digital nerve, and the ulnar proper nerve. The deep branch innervates the hypothenar muscles, opponens digiti minimi, interosseous muscles, lumbricals, adductor pollicis, and the medial head of the flexor pollicis brevis.
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Frequently asked questions
The palmar interossei are intrinsic muscles of the hand that occupy the spaces between the metacarpal bones. They are strong adductors of the fingers.
The main function of the palmar interossei is to adduct the fingers in a longitudinal axis, which means the movement of the fingers towards the middle finger.
The adductor pollicis muscles are large triangular muscles with two heads. One head originates from metacarpal III, and the other from the capitate and adjacent areas of metacarpals II and III. Both attach to the base of the proximal phalanx of the thumb.
The adductor pollicis muscles provide power for pinching. They help fill the first web space between the thumb and index finger.
The palmar interossei muscles are smaller than the dorsal interossei and are situated on the palmar surface of the hand. They are adductors of the fingers, while the dorsal interossei abduct the fingers.
