Sensory signal(^) Serotonin (^) from siphon
neurotransmitter
Sensory signal
from tail
Glutamate
VINA: neurotransmitter
Motor signal
to withdraw gill
Figure 19.4. Synaptic connections in Aplysia californica.
If a strongly aversive sensory stimulus (such as an electric shock) is
applied to the animal's tail region around the same time as touching
of the siphon, an increased robustness of gill withdrawal in response
to touching is observed. This increased robustness has been linked to
transient strengthening of the synaptic connection linking the siphon
sensory neurons with the motor neurons mediating the retraction of
the gill.