Figure 3.
Lamprey spinal cord intersegmental coordination. A, During swimming, a mechanical wave activating the muscles is transmitted along the spinal cord. When the animal moves forward, there is a lag between consecutive segments in the spinal cord. This lag is always a certain proportion of the cycle duration (i.e., a constant phase lag). It can be reversed into a wave that is propagated from tail to head, as during backward swimming. A rostral-to-caudal lag is also seen in the isolated spinal cord preparation. This pattern can be reversed if, for example, extra excitation is added to the caudal spinal cord. B, Ionic membrane and synaptic events important during activation within the CPG network. Slower processes can cause spike frequency adaptation, like Ca2+ accumulation during ongoing spiking and resulting activation of KCa. LVA, Low-voltage activated; Ipsi, ipsilateral; Contra, contralateral. C, Raster plots of the rostrocaudal activation of each of the 3000 EIN neurons in the model hemicord network (corresponding to 100 segments) during spontaneously forming forward swimming. Seg, Segment. D, The model lamprey swimming in water is simulated using a neuromechanical model of the muscles activated by the output from local CPG neurons.