This essay looks at the historical significance of five APS classic papers that are freely available online: McPhedran AM, Wuerker RB, and Henneman E. Properties of motor units in a homogeneous red muscle (soleus) of the cat. J Neurophysiol 28: 71–84, 1965 (http://jn.physiology.org/cgi/reprint/28/1/71). Wuerker RB, McPhedran AM, and Henneman E. Properties of motor units in a heterogeneous pale ...