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Discussions on simulating the worm's crawling by means of command neurons, motor neurons and muscle cells #82
In a series of documents, I will discuss the role of the command-neurons, different types of motor neurons and their connectivity with the body-wall muscle cells. The ultimate goal is to derive a valid assumption on how the crawling happens in C. elegans and accordingly, simulate the response of the worm to a tap or touch stimulus in C302 and Sibernetics. My justifications will be based on the connectome dataset provided for the adult hermaphrodite by the WormWiring . I will be investigating various neural circuits consisting of command neurons such as AVB and AVA, together with B-type, A-type, D-type and AS motor neurons including their connectivity to the muscles. The first discussion will be on a neural circuit comprised of AVB and B-type motor neurons. I will then discuss D-type and AS motor neurons within the next discussion. Afterwards, I will include the body-wall muscles into the neural circuit and discuss in details the propagation of an AVB-excitation into the motor neurons and muscle cells. I will finally repeat such analyses with AVA command neuron and A-type motor neurons and explain the neural circuit's architecture.
1) On the importance of the command neuron AVB and B-type motor-neurons in the worm’s crawling:
AVB command neuron together with B-type motor neurons function in the deriving the forward locomotion. There are seven dorsal and eleven ventral B-type motor neurons spread over the body of the worm. Considering a neural circuit, shown in Figure 1A and 1B, consist of only AVBL/R and all the B-type motor-neurons on the dorsal and ventral sides, one can highlight some attractive fundamental architectural design properties within the circuit:
Such property has been observed also within the D-type dorsal and ventral motor neurons which will be explained in the next discussion.
I'd suggest that these hypotheses can have tests built around them via c302 models to explore their implications.
referenced this issue
Mar 17, 2017
2) Proprioception in motor neurons is key for generating the forward locomotion
Even when all the command interneurons were knocked out, C. elegans was able to generate the crawling . This suggests the significant role of motor neurons in propagation of the bending waves.
In general, rhythmic behavior is exhibited in animals thanks to the existence of neural circuits named as central pattern generator (CPG) . There can be groups of CPG networks distributing rhythmic activities in an organism. CPG networks therefore should get coordinated with each other. Usually a sensory feedback mechanism exists for such coordination [3, 4, 5].
In C. elegans however, such sensory feedback does not exist due to lack of advanced sensory neurons. Accordingly, one argument suggests that the proprioceptive property can be "economically" exhibited by means of individual motor neurons [6, 8]. Electron microscopy illustrated that particularly cholinergic motor neurons (e.g. B-type), induce asynaptic processes all along the posterior without synaptic connections [6, 8]. Such mechanisms have been hypothesized as a proprioception process.
Wen et al. in , conducted wonderful experiments on quantification of proprioception in the B-type motor neurons of C. elegans.
Figure 1. (Taken from ) Symbolic representation of connections from DB and VB motor neurons to some muscle cells through their neuromuscular junctions (Triangles) and their axons along the body of the worm. The asynaptic process shown in the figure illustrates the potential proprioceptive effect of the B-type motor neurons by means of their axons. Axons of the anterior DB motor neurons extend along the body of the worm to the posterior side making it possible to propagate a bending wave .
According to such findings, I believe for modeling the crawling of C. elegans, in our neuron or muscle model one should properly include the biomechanics of the undulatory movement in order to include the proprioception mechanisms.
We will try this soon together with David! @lungd
Sub-roadmap for the nervous system simulation