ABSTRACT
Premotor cortical neurons synapse with brainstem reticular neurons that go to axial and proximal limb muscles to provide the initial orientation of the body and limb towards a visual target. The supplementary motor area controls proximal limb muscles directly via its output to the corticospinal tract, but exerts control on distal limb muscles via its connections with motor cortex (MI). The long loop modifies muscle contraction on a time scale slower than that of the myotatic reflex, but faster than voluntary movements. Recording from single cells in the motor cortex of conscious monkeys engaged in intentional limb movements shows that MI cell firing can correlate with force, rate of change of force, velocity, acceleration, direction of movement or joint position. Some pyramidal cells in layer V of the motor cortex send their axons in the corticorubral tract to the magnocellular part of the red nucleus in the midbrain, which also receives collaterals from the corticospinal tract.
