Figure 2.

Pyramidal cells of the cat motor cortex give rise to an extensive network of horizontal axon collaterals. The motor cortex is bounded laterally by the coronal sulcus (Co.S.), the location of the coronal gyrus is demarcated by the dashed lines - - -. The areas anterior and posterior to the cruciate sulcus, along with the coronal gyrus, constitute the cat primary motor cortex. Biocytin, an anterograde tracer, was injected in points marked by a red circle. Threshold level microstimulation at that point evoked activity in the brachialis muscle in (A) and the extensor carpi radialis in (B). Note how the axon collaterals of pyramidal cells from both deep and superficial layers of a small cortical locus spread to cover nearly all of the forelimb representation area [figure modified from Capaday et al. (2009)].