Hey there! It’s Matt from Kenhub, and in this tutorial, we will discuss the palmar interossei muscles. The palmar interossei muscles are three unipennate muscles located in the metacarpus. They arise from the metacarpal bones of the index, ring, and little fingers or fingers 2, 4 and 5 respectively.
The surfaces of origin of all three of these muscles face towards the middle finger and are located on the shaft of the finger they act on, fingers 2, 4 and 5 to be exact. For example, as you can see here on the palmar interosseus muscle 1 highlighted in green on this first image, it has its origin on the ulnar side of the second metacarpal. Even though the palmar interosseus muscle 2 has its origin on the radial side of the fourth metacarpal and the palmar interosseus muscle 3 has its origin on the radial side of the fifth metacarpal bone, both their muscle bellies face the middle finger, as you can see on the images.
The muscles insert at the dorsal aponeurosis and the base of the proximal phalanx of their respective finger. Note that the middle finger itself does not have its own palmar interosseus muscle. The nerve supply to these muscles is provided by the deep branch of the ulnar nerve.
The most important function of the palmar interossei muscles is the closing of spread fingers, which means the movement of the fingers towards the middle finger. In other words, the contraction of the palmar interossei muscles results in the adduction of the little finger, ring finger and index finger toward the middle finger. Other functions include flexion of the metacarpophalangeal joint and the extension of the interphalangeal joint on those same fingers.
Functionally, the palmar interossei act antagonistically to the dorsal interossei in the MCP. There is a mnemonic that can help you remember this. DAB equals Dorsals ABduct. PAD equals Palmar ADduct. However, both muscle groups perform common functions as they flex the fingers in the metacarpophalangeal joints and extending the proximal and distal interphalangeal joints.
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