Final answer:
The summation effect refers to the cumulative action of multiple stimuli that collectively can reach the threshold potential to trigger an action potential and cause the sensation of itch. Spatial and temporal summation allow subthreshold stimuli to integrate and lead to significant sensory experiences, including the sensation of itch.
Step-by-step explanation:
The summation effect in the threshold of itch refers to the process where multiple subthreshold stimuli combine their effects to reach the threshold potential necessary to trigger a sensation of itch. In the nervous system, neurons integrate signals both spatially and temporally. Spatial summation involves multiple stimuli occurring at different locations on the membrane, whereas temporal summation involves stimuli that occur at different times. If the combined depolarization from these stimuli is sufficient to exceed the threshold of the neuron, an action potential will be initiated, potentially leading to the perception of itch.
For example, rather than one weak stimulus acting alone, multiple weak stimuli can summate over time to reach the threshold level needed to create an action potential. In terms of sensations like itch, this means that multiple small stimuli can accumulate until the sensory neurons reach a threshold and signal the brain, which interprets this as itch. This is important in filtering out noise, ensuring that only significant stimulation results in a perceptible itch sensation.