A morphological study of the axons and recurrent axon collaterals of cat alpha‐motoneurones supplying different functional types of muscle unit.

Abstract

SUMMARY1. Cat a-motoneurones supplying muscle units of the soleus S type and gastrocnemius S, FR and FF types were injected intracellularly with horseradish peroxidase.2. Ten a-motoneurones of each motor unit type were collected for morphological analysis of the intramedullary parts of their axonal systems including the recurrent axon collaterals.3. The a-motor axon diameters in the spinal cord white matter were significantly smaller for the soleus motor units (mean = 5-2 jtm) than for the gastrocnemius S units (mean = 6-4 #m), which in turn differed significantly from those of the gastrocnemius FR (mean 7 4 sum) and FF (mean = 7 3 ,um) types.4. The number of axon collateral outbulgings, interpreted as synaptic terminals, which originated from the soleus motor axons (mean = 27-8) was significantly smaller, while that of the gastrocnemius FF motor axons (mean = 98.1) was significantly larger, than the number of outbulgings from the gastrocnemius S (mean = 44.4) and FR (mean = 53.8) motor axons. The latter two types were not significantly different.5. In transverse sections the axon collateral outbulgings were found not only in the classical Renshaw cell area ventromedial to the main motor nuclei but also within the homonymous motor nucleus. However, only some of the neurones projected to the latter area. Rostrocaudally, the outbulgings were distributed within a distance of less than 1 mm around the position of the parent cell bodies.6. Some physiological implications of the observed differences between axon collateral systems of various functional types of ac-motoneurones were discussed in relation to the present knowledge of the effects of the recurrent axon collaterals during different types ofinvoluntary and voluntary activation ofthe a-motoneurones.

Adaptive neural networks for control of movement trajectories invariant under speed and force rescaling

“…526)." In particular, Pompeiano and Wand (1976;Wand and Pompeiano, 1979) a size-dependency, and Cullheim and Kellerth (1978) produced convergent anatomical evidence by showing that larger, phasic motoneurons make many more synaptic contacts with Renshaw cells than smaller, tonic motoneurons. The second hypothesis has been well supported since Sherrington's (1906) observations of reciprocal inhibition, but is oddly ignored in many treatments.…”

“…Suppose that a co-contractive input, P, to a-MN 1 and a-MN 2 occurs when input A 1 exceeds A 2 and that the activity of a-M N 1 is consequently multiplied by a larger factor than that of a-M Nz due to the size principle (Figure 8). Then R 1 also becomes much more active due to a size-correlated synaptic weighting on a-M N 1 axon collaterals to R 1 ( Cullheim and Kellerth, 1978;Pompeiano, 1984). Because the opposing R 2 has not experienced as large an input increment, R 1 will transiently become more active than R 2 by an amount that scales with the difference between the a-MN output increments due to the change in P. Thus, this system calculates a predicted error due to unequal amplifications of co-contractive inputs.…”

Simulation system of spinal cord motor nuclei and associated nerves and muscles, in a Web-based architecture

“…The spatial positioning of the neurons in the simulated neuronal columns is specially important because RC synapses on MNs (and vice-versa) occur among synergistic nuclei (McCurdy and Hamm 1994a, b), with synaptic strength depending on the distance between the cells (Cullheim and Kellerth 1978;Windhorst 1996;Burke 2004).…”

“…On the other hand, one MN reaches a smaller number of RCs (Cullheim and Kellerth 1978;Burke 2004). The influences of a RC over the MN pool and the influence of a MN over the RC pool diminish with distance, modeled according to Eq.…”

“…For the synapses from MNs to RCs, the factor a was set at 0.01, because the maximum spread of the MN collaterals reaches 1 mm (Cullheim and Kellerth 1978;Burke 2004). …”