Final answer:
Short-term habituation in Aplysia involves a decrease in synaptic strength with repeated exposure to a stimulus, while sensitization involves an increase in synaptic strength in response to an intense or noxious stimulus.
Step-by-step explanation:
The steps in short-term habituation and sensitization of Aplysia involve changes in the strength of synaptic connections between neurons. In habituation, repeated exposure to a stimulus leads to a decrease in response. This occurs as the sensory neurons release less neurotransmitter onto motor neurons, weakening the synaptic connection. Conversely, in sensitization, an intense or noxious stimulus can strengthen connections. This often involves the release of serotonin in the neural circuit, which increases the synaptic activity, thereby enhancing the response to a stimulus.
For an example, referring to the research in the lab of David Glanzman, Aplysia can be trained to withdraw its siphon in response to a mild touch after repeated trials, illustrating habituation. In contrast, if the touch is strong or paired with a harmful stimulus, sensitization occurs, and the siphon withdrawal becomes more pronounced. This process of habituation and sensitization in Aplysia is a valuable model for understanding the cellular mechanisms underlying learning and memory in more complex organisms.