Table 2  Comparison of α- and γ-spinal motor neurons.
Spinal α-MN  Spinal γ-MN
Target muscle fiber  Extrafusal1  Intrafusal1
Soma size  Larger2,3,4,5  Smaller2,3,4,5
Axon diameter  Larger2  Thinner2
Dendrite branching  More2  Less2
Motor unit size (innervation ratio)  Larger6  Smaller6
Membrane input resistance  Larger7  Smaller7
Firing  Subtype-dependent8  Subtype-dependent8
Axon conduction velocity  Faster2,7,9  Slower2,7,9
Afterhyperpolarization duration  Subtype-dependent7,9  Variable7,9
Spinal reflex  Yes10  No10
Affected in ALS  Yes11,12  Less11,12
Affected in aging  Yes13,14  No13,14
Markers  Osteopontin15RBFOX3/NeuN16Hb9::GFP5NKAα117 (adult)  Err316Weak NeuN5,16NKAα317 (adult)ESRRG16GFRα15HTR1D18 (early marker)WNT7A19 (late embryonic stage)
ESRRG, estrogen-related receptor gamma; GFRα1, GDNF family receptor alpha 1; HTR1D, serotonin receptor 1D; NAKα1/3, Na+/K+-ATPases 1/3; RBFOX3, RNA binding protein fox-1 homolog 3. 1(Kuffler et al., 1951), 2(Burke et al., 1977), 3(Westbury, 1982), 4(Friese et al., 2009), 5(Shneider et al., 2009), 6(Adal and Barker, 1965), 7(Kemm and Westbury, 1978), 8(Murphy and Martin, 1993), 9(Gustafsson and Lipski, 1979), 10(Eccles et al., 1960), 11(Mohajeri et al., 1998), 12(Lalancette-Hebert et al., 2016), 13(Swash and Fox, 1972), 14(Hashizume et al., 1988), 15(Misawa et al., 2012), 16(Friese et al., 2009), 17(Edwards et al., 2013), 18(Enjin et al., 2012), 19(Ashrafi et al., 2012).