These differences may reflect their diverse embryological origin, the different milieu in the brainstem, or differences in the structure and function of oculomotor units compared to motor units of other skeletal muscles.
In EDL muscles of SOD1G93A mice, there is a significant reduction in the number of surviving motor units at 120 d compared to wildtype littermates.
The findings are consistent with the interpretation that during position tasks more motor units are being recruited compared with force tasks, and the discharge rate of MUs is higher (Mottram et al. 2005a).
39 The minimal rise of MUNE measurements over the first 2 weeks of life in SMNΔ7 mice compared to rising estimates in controls is consistent with falling numbers of functional motor units in the SMNΔ7 mice compared with stable populations in controls (Fig. 3B).
The summation of contractile forces of motor units (MUs) was analyzed by comparing the recorded force during parallel stimulation of two and four individual MUs or four groups of MUs to the algebraic sum of their individual forces.
The firing rate and recruitment threshold of motor units decomposed from EMGs were then compared among muscle regions.
Synapses formed on Fast Synapsing (FaSyn) muscle, or by fast-fatiguable (FF -type motor units exhibit relatively little synaptic plasticity, compared to Delayed Synapsing (DeSyn) or slow (S)-type motor units.
If the muscles of adult males contain a greater number of type IIb muscle fibers than do those of boys and elderly males, then it is understandable why the muscles of boys and elderly males are more resistant to LFF, since it has been established that in cat skeletal muscles, fatigue-resistant motor units are less susceptible to LFF compared with fast-fatigable motor units [ 32].
However, although muscle force is still maintained in all muscle types investigated, in 24-week-old SOD1 G93Adl B6 mice there was a significant reduction (P<0.001) in the number of motor units that innervate the EDL muscle, compared with wild type (Fig. 4B).
When comparing the number of motor units recruited during a voluntary contraction, the children with cerebral palsy had less units than the healthy children [ 1].
