Final answer:
Stimulating the tail of an Aplysia causes synaptic potentiation in the motor neuron of the gill. This phenomenon is characterized by the strengthening of synaptic connections, facilitated by calcium influx and neurotransmitter release at the neuromuscular junction.
Step-by-step explanation:
Stimulating the tail of an Aplysia causes synaptic potentiation in the motor neuron of the gill. Synaptic potentiation refers to the process by which synaptic connections are strengthened, leading to an increased response in the postsynaptic neuron. When an action potential reaches the axon terminals, it triggers the opening of voltage-gated Ca2+ channels, resulting in an influx of calcium ions which facilitate the release of neurotransmitter molecules like acetylcholine (ACh) from synaptic vesicles into the synaptic cleft. The neurotransmitter then binds to ACh receptors on the sarcolemma of the muscle fiber at the neuromuscular junction (NMJ), inducing a depolarization that can lead to muscle fiber contraction.