Fig. 1
Spinal cord computational model. (a) Distribution of motor neuron pools for each muscle within the spinal cord: the motor neuron pool innervating the tibialis anterior (TA) is distributed across L3 (20%), L4 (70%), and L5 (10%); for the gastrocnemius (GC), it is located in L4 (20%), L5 (60%), and L6 (20%); for the vastus medialis (VM), the distribution is in L2 (20%), L3 (70%), and L4 (10%); and for the semitendinosus (ST), the pool spans L4 (20%) and L5 (80%). (b) The spinal cord segment at L4 includes gray matter, white matter, cerebrospinal fluid, dura, electrode contact, electrode insulation, Aα-sensory fibers, and α-motor fibers. (c) Multicompartment cable models of myelinated axons are constructed, with each node (NODE) represented by one segment and each internode divided into ten segments: two MYSA, two FLUT, and six STIN segments. (d) The node and internode segments are modeled with fast K⁺ (Kf), slow K⁺ (Ks), fast Na⁺ (Na), persistent Na⁺ (Nap), leak current (Lk), and HCN (H) channels, along with nodal (Cn), internodal (Ci), and myelin (Cm) capacitances, as well as axoplasmic (Ga), periaxonal (Gp), and myelin (Gm) conductances. (e) The FEM mesh and the spatial arrangement of the fibers.
