Reported differences between the vulnerable (ventral spinal cord MNs) and resistant (oculomotor) motor neurons in ALS. The surface area and axonal conduction velocities referred to here were obtained from studies in cats (Westbury, 1982). The α-MNs innervate highly contracting extrafusal fibers, whereas γ-MNs innervate intrafusal fibers that contract much less; oculomotor neurons innervate the extraocular muscles in the orbit. α-MNs are larger than γ-MNs and oculomotor neurons and possess more dendritic trees. α-MNs are further subdivided based on their size and function. The proteins listed at the bottom of the figure are those enriched in each MN population.