The transcriptional changes observed in VEGFδ/δ mice would be predicted to result in a reduced capacity for the morphological adaptations that occur during plasticity of the motor unit, resulting in increased vulnerability to degeneration.
However, our study of motor unit number highlighted the differential vulnerability of these muscles and showed that the fast twitch TA and EDL muscles are more severely affected (earlier effect, greater loss of motor units) than the slow twitch soleus muscle.
One study has investigated the various aspects of differentially vulnerable motor units, including motor unit size, muscle fibre type, NMJ size, branching patterns and Terminal Schwann cell number but found no correlation with differential vulnerability [ 49].
G93A-SOD1 toxicity has already been shown to increase the vulnerability of motor neurons and muscles to sciatic nerve injury, by reducing the post-injury motor unit survival whilst impairing the muscle contractile characteristics [ 17].
Rate coding governs motor unit firing.
According to kinesiologist and author Roger Enoka, motor unit recruitment is based on the size principle, which states that the motor units that recruit slow-twitch fibres recruit fewer fibres than the motor units that recruit fast-twitch fibres.
CT assessment of motor unit action potentials.
The basic functional unit of muscle is the motor unit.
Fatigue effect on motor unit activity during submaximal contractions.
Repeated contractions led to earlier motor unit changes and fatigue.
