Motor systems II: Descending (cortical) systems

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Summary of corticospinal circuit connections mediating fine control of the wrist and fingers, as indicated by experiments in awake, behaving monkeys. A F, clusters of pyramidal tract neurons in the motor cortex. Groups (pools) of motoneurons to different types of muscles: the six extensors were extensors carpi ulnaris (ECU), digitorum communis (EDG), digitorum 2 and 3 (ED2, 3), digitorum 4 and 5 (ED4, 5), carpi radialis longus (ECR-L), and carpi radialis brevis (ECR-B); the six flexors were flexors carpi radialis (FCR), digitorum profunds (FDP), carpi ulnaris (FCU), digitorum sublimis (FDS), plamaris longus (PL), and pronator teres (PT). Open profiles excitatory actions; filled profiles, inhibitory actions.