Limitations in the Neural Control of Human Thumb and Finger Flexors
Of all primates, humans have the greatest capacity to make independent movements. Factors contributing to this capacity include morphological changes in humans, e.g. the presence of flexor pollicis longus in humans. However, there are limitations to independent movement due to kinaesthetic and neural factors as well as to biomechanical linkages. Psychophysical studies have been used to study kinaesthesia in human subjects. The subjects’ ability to grade forces produced by intrinsic and extrinsic muscles of the hand was limited although forces produced by the thumb were more accurately perceived than those produced by the index finger. Also, there was limited kinaesthetic independence between forces generated by neighbouring muscles. Using EMG recordings from fine-wire intramuscular electrodes, neural limitation to voluntary recruitment of the long flexor muscles can be demonstrated: co-contraction of adjacent muscles occurred when weak contractions were made by a long finger flexor. In summary, although humans have greater capacity than other primates to perform independent movements with their digits, this ability is limited.
KeywordsMotor Command Flexor Muscle First Dorsal Interosseous Intrinsic Muscle Adductor Pollicis
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