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P2 is a motor neuron in the Aplysia californica pedal ganglia.

Figure 1. 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. Identified motor neuron P2 is shown at lateroanterior portion of sector II. Modified from Hening et al 1979.

Basic Information

  • No known alias
  • Neurotransmitter is as yet unidentified



P2 is a 100-150um cell, and is light in pigment. It is located on the medioanterior pedal ganglion, adjacent to the cerebropedal connective in sector II, usually adjacent to P3 (Fig. 1). P2 is considered to be a transverse contractor motor neuron, with innervation to the mesosegments of the Aplysia californica foot (Hening et al. 1979).


When stimulated in intact animals, P2 causes a large contraction dorsoventrally in the lateral tegument, and also a transverse contraction of the second and possibly the third and first segments of the foot, although there appears to be no longitudinal contraction effect. Therefore, P2 is considered to be one of the mesosegmental motor neurons. While the animal is moving, P2 receives both depolarizing and hyperpolarizing stimuli. It is known to send axons to pedal nerves 8 and/or 9 (Hening et al. 1979).

Figure 2. P2 stimulation and locomotion in Aplysia californica. A Tension as recorded by movement of transducer attached to mesotegumental region of animal corresponds with firing in motor neuron P2 after salt stimulation in vivo. B In vitro recording of P2 in isolated circumesophageal ganglia shows that after brief shock to P2, the motor neuron fires in a regular pattern reminiscent of firing recorded in vivo during movement shown in A. Modified from Hening et al 1979.


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.