"Although motoneurons have often been considered
to be fairly linear transducers of synaptic input, recent evidence
suggests that strong persistent inward currents (PICs) in motoneurons
allow neuromodulatory and inhibitory synaptic inputs to induce large
nonlinearities in the relation between the level of excitatory input and
motor output. To try to estimate the possible extent of this nonlinearity,
we developed a pool of model motoneurons designed to replicate
the characteristics of motoneuron input-output properties measured in
medial gastrocnemius motoneurons in the decerebrate cat with voltage-
clamp and current-clamp techniques. We drove the model pool
with a range of synaptic inputs consisting of various mixtures of
excitation, inhibition, and neuromodulation. We then looked at the
relation between excitatory drive and total pool output. Our results
revealed that the PICs not only enhance gain but also induce a strong
nonlinearity in the relation between the average firing rate of the
motoneuron pool and the level of excitatory input. The relation
between the total simulated force output and input was somewhat
more linear because of higher force outputs in later-recruited units. ..."
Reference:
1 .
Powers RK, Heckman CJ (2017) Synaptic control of the shape of the motoneuron pool input-output function. J Neurophysiol 117:1171-1184 [PubMed]
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