PubMed · 5370677
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E B Kaplan, P Nathan. 1969. Accessory extensor pollicis longus.. https://pubmed.ncbi.nlm.nih.gov/5370677/
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Pianists were asked to play short excerpts from several pieces on an electronic keyboard. In each piece, there were two phrases whose first few notes were played identically with the right hand. Thereafter, the two phrases were played differently. The aim of the investigation was to ascertain whether or not hand and finger kinematics diverged prior to the depression of the last common note. Such a divergence would imply an anticipatory modification of sequential movements of the hand, akin to the phenomenon of coarticulation in speech. The lack of such a divergence would imply a strictly serial organization of movement sequences with one hand, as was found previously to be the case for typing. The time at which each key was depressed and released and the speed with which the key was depressed was recorded via a MIDI interface to a laboratory computer. The motion of the right wrist and of the fingers of the right hand was recorded optoelectronically. Piano playing can invoke anticipatory modifications of hand and finger kinematics. The time at which two patterns of movements diverged varied considerably from piece to piece. Playing an ascending scale with the requirement of a "thumb-under" maneuver could evoke an anticipatory modification as much as 500 ms in advance of the last common note. In another piece, keypresses appeared to be executed in a strict serial ordering and a third piece gave results intermediate between these two extremes. We interpret the results to suggest that a strict serial execution of a movement sequence is favored as long as this is compatible with the demands of the task.
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The complexity and intricacy of hand function are reflected by the anatomy. Extensor muscles have a relatively consistent architecture but also have notable anatomic variations of their tendons, particularly on the ulnar side of the hand. The extensor tendons, juncturae tendinum, intertendinous fascia, and soft tissue function as a plexiform construct to provide stability during power grip and allow for laxity in performing independent fine finger tasks. The greater independence of index finger motion relates to its two tendons, one (EDC-index) with a thin transverse juncturae tendinum, the other (EIP) without a junctural connection. It is also more independent because of a more mobile metatarsal, and because it is confined by only one web. The first dorsal interosseous also functions to rotate the index finger. The lumbrical to the index finger has only a single origin on the flexor profundus tendon. The elaborate tendon plexus on the dorsum of the hand is repeated in the complexity of the dorsal aponeurosis on the dorsum of the fingers. Finger motion is a balance of flexor muscles and intrinsics and extensor muscles that provides incredible versatility. This versatility and delicate balance of function is easily jeopardized by trauma and disease. The hand is among the most frequently injured parts of the body. An appreciation and understanding of its complex anatomy is of importance to hand assessment, repair, and reconstruction.