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. 2014 Mar 19:8:85.
doi: 10.3389/fncel.2014.00085. eCollection 2014.

Excitability properties of single human motor axons: are all axons identical?

Lydia P Kudina  1 , Regina E Andreeva  1
Affiliations

Excitability properties of single human motor axons: are all axons identical?

Lydia P Kudina et al. Front Cell Neurosci. .
No abstract available

Keywords: axonal excitability recovery; motor control; single firing motor units; superexcitability; voluntary muscle contraction.

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Figures

Figure 1
Figure 1
Single motor axon excitability testing by mixed nerve stimulations during voluntary muscle contractions. (A) Examples of MU recordings. Two top records, an MU of group 1 displaying both the H-reflex and M-response; two bottom records, an MU of group 2 displaying M-response only. Asterisks, stimulation time. (B) Peri-stimulus time histograms (PSTHs) of single MUs. Top, an MU of group 1 showing a significant increase in firing probability at the M-response and H-reflex latencies (the tibialis anterior, 2462 trials). Bottom, an MU of group 2 displaying a significant increase in firing probability at the M-response latency only (the flexor carpi ulnaris, 379 trials). M-response was observed in 6.9% trials in top PSTH and in 90.1% trials in bottom PSTH. Zero, stimulation time. The bin width, 2 ms. (C) Distributions of target and background ISIs of single MUs. Top, three MUs of group 1 from one experiment (the tibialis anterior); bottom, an MU of group 2 (the flexor carpi ulnaris). Target ISIs (open bars), n = 257 in top and n = 421 in bottom; background ISIs (filled bars) from the same trials. Bin width, 5 ms. (D) Testing of changes in axonal excitability throughout a target ISI of single MUs. Top, an MU of group 1 (the tibialis anterior, 897 trials); bottom, an MU of group 2 (the flexor carpi ulnaris, 294 trials). Changes in the firing index (FI) after a regular voluntary discharge (taken as 0 ms) are shown within the first 50 ms of the target ISI. The remaining part of the ISI, in which the FI continued to be equal to 0% (in top) and to 100% (in bottom), is not shown. Note bin width of 2 ms within 0–20 and 5 ms within 20–50 ms of the target ISI.
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