Movements, neurons and network organization underlying feeding in Lymnaea. (A) There are four phases in the feeding ingestion cycle. During the protraction phase the buccal mass and radular rotate forwards, the mouth opens and by the end of this phase the radular is pressed on the food substrate. During rasp the radular begins to rotate backwards and scoops the food into the buccal cavity. During swallow the mouth closes and the radular continues to rotate backwards to push the food into the esophagus. The rest phase is a period of inactivity between feeding cycles. In fast rhythms such as the one shown in Figure 2A the rest period is reduced to zero. (B) Map of feeding neurons in the buccal ganglia (buccal g.) and cerebral ganglia (cerebral g.). There are symmetrical sets of neurons on left and right side except for the SO that is a single cell that can be either on the left or right side. Unshaded neurons are motoneurons (B1 to B10, CV3, C5 to C7). Shaded neurons are CPG interneurons (N1M, N1L, N2d, N2v, N3p and N3t), modulatory interneurons (OC, SO and CGCs), initiating neurons (CV1a) and sensory neurons (OM). CV1a is part of a larger population of CBIs and the complete map of their locations is shown in Figure 3A. A = anterior; CBC = cerebrobuccal connective; L = left; MLN = median lip nerve; P = posterior; R = right, SLN = superior lip nerve. (C) Synaptic connectivity and functions of neurons in the feeding circuit. Modulatory function is indicated by yellow and initiating function by orange. CPG interneurons and motoneurons active during the three phases of the feeding rhythm are indicated by green (P = protraction), blue (R = rasp) and red (S = swallow). Neurons labeled with two colors have two functions. Dots indicate inhibitory chemical synapses, bars excitatory chemical synapses and resistor symbols electrotonic (electrical) synapses. This figure emphasizes the point that many of the neurons have more than function in the feeding network. See Abbreviations for all definitions of neuron types.