ESSAYS ON APS CLASSIC PAPERS The size principle: a rule describing the recruitment of motoneurons

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 muscle (m. gastrocnemius) of the cat. J Neurophysiol 28: 85–99, 1965 (http://jn.physiology.org/cgi/reprint/28/1/85). Henneman E, Somjen G, and Carpenter DO. Functional significance of cell size in spinal motoneurons. J Neurophysiol 28: 560–580, 1965 (http://jn.physiology. org/cgi/reprint/28/3/560). Henneman E and Olson CB. Relations between structure and function in the design of skeletal muscles. J Neurophysiol 28: 581–598, 1965 (http://jn.physiology. org/cgi/reprint/28/3/581). Henneman E, Somjen G, and Carpenter DO. Excitability and inhibitability of motoneurons of different sizes. J Neurophysiol 28: 599–620, 1965 (http:// jn.physiology.org/cgi/reprint/28/3/599).