Spinal α-MN
F  S
Target muscle fiber  IIb (FF), IIa (FR)1  I1
Soma size  Similar2,3,4,5,6  Similar2,3,4,5,6
Axon diameter  Larger7,8  Thinner7,8
Dendrite branching  More4,9  Less4,9
Motor unit size (innervation ratio)  Larger1,10  Smaller1,10
Membrane input resistance  Smaller11,12,13  Larger11,12,13
Firing  Phasic14,15  Tonic14,15
Axon conduction velocity  Faster1,13  Slower1,13
Afterhyperpolarization duration  Shorter14  Longer14
Recruitment  Late15  Early15
Affected in ALS  Early16,17,18  Late16,17,18
Affected in aging  Early19,20,21  Late19,20,21
Markers  CHODL22 CALCA22  SV2a23 SK324 ESRRB22 (adult)