Aplysia californica pedal ganglia

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The paired pedal ganglia of Aplysia californica are the most caudal portion of the circumesophageal ganglia. The pedal ganglia are bilaterally symmetrical and are connected by two commisures and two connectives (Fig. 1).

Figure 1. Schematic representation of the Aplysia central nervous system that contains 9 major ganglia including paired buccal (BG), pedal (Pe), pleural (Pl), and cerebral (CG) and a single abdominal (AG) ganglion. Modified from Moroz et al.

Pedal ganglia sectors

Figure 2. Schematic representation of the dorsal Aplysia pedal and pleural ganglia. Left pedal ganglion shows designated sectors, right pedal ganglion shows approximate locations of identified neurons. Modified from Hening et al 1979.

Each pedal ganglion's dorsal surface is divided by septa in to distinct clusters of cell bodies. These sectors were originally numbered and identified by Henning et al. 1979 (Fig. 2).

Sector Ia and Ib

Darkly pigmented cells lining the pedal commisure medially in each ganglion.

Sector II

Medio-anterior in each ganglion. Identified cells in sector II: RP5, P2, P3, P4

Sector IIIa

Latero-anterior in each ganglion. Identified cells in sector IIIa: P1

Sector IIIb

Latero-posterior in each ganglion.

Sector IIIc

Medio-posterior in each ganglion.

P5, P6, and P7 have cell bodies in quadrant 3.

Pedal ganglia motor neuron types

Several neuron types were identified in the pedal ganglion by Hening et al. 1979. These neurons may be divided in to three types, based on the portion of the animal that they control: prosegmental motor neurons, mesosegmental motor neurons, and metasegmental motor neurons. (Fig. 3)

Figure 3. Schematic representation of the Aplysia body, divided to illustrate target regions of pedal ganglia nerves. Modified from Hening et al, 1979.

Pedal ganglion nerves

The pedal ganglia are connected to other ganglia through large connectives: the Pedal-Pleural connective and the Cerebro-Pedal connective. In addition, there are two commissures that connect the left and right pedal ganglia: the large commissure is known simply as the Pedal Commissure, the smaller, more anterior commissure is called the parapedal commissure. The nerves leaving the pedal ganglion are numbered in an anterior to posterior fashion (P1-P10). Unlike the other nerves, P10 is a midline nerve that exits from the parapedal commissure.

Cobalt backfilling of the 9 paired nerves by Hening et al., 1979, indicates that each nerve contains axons of neurons from several cell clusters that are dispersed through the ganglion.


1. Hening, W.A., Walters, E.T., Carew, T.J., Kandel, E.R. (1979) Motorneuronal control of locomotion in Aplysia. Brain Research, 179. 231-253.

2. Moroz et al.

3. Walters, E.T., Byrne, J.H., Carew, T.J., Kandel, E.R. (1983a) Mechanoafferent neurons innervating tail of Aplysia. I. Response properties and synaptic connections.