FIGURE 5-9 Renshaw Loop Left: Some spinal cord motor neurons project to the rat’s forelimb muscles. Right: In a Renshaw loop the main motor axon (green) projects to a muscle, and its axon collateral remains in the spinal cord to synapse with a Renshaw interneuron (red). The Renshaw interneuron contains the inhibitory transmitter glycine, which acts to prevent motor neuron overexcitation. Both the main motor axon and its collateral terminals contain acetylcholine. When the motor neuron is highly excited, it can modulate its activity level through the Renshaw loop (plus and minus signs).

Ian Whishaw