Final answer:
Summation refers to the process where multiple graded potentials can add up to reach the threshold for an action potential. The threshold for stimuli, such as itch, may not be the same for all animals due to differences in species-specific physiology. This subject requires more detailed species-specific research to draw accurate conclusions.
Step-by-step explanation:
The concept of threshold of itch and summation effect pertains to how neurons process signals. Summation occurs when multiple graded potentials add together, potentially leading the neuron to reach threshold, which is the critical level needed for an action potential to be initiated. This is relevant for understanding sensory responses like itching. It's known that spatial summation can occur across different segments of the membrane or temporal summation over time, with postsynaptic potentials either adding up (depolarization) or canceling out (hyperpolarization).
Regarding the question of whether the threshold is the same for all animals, there is a variety of factors to consider, including species-specific physiology and ecological factors. As suggested by studies such as those on the deer ked's preferences for temperature and body parts or the relationship between animal behavior and the abundance threshold for disease, there could be differences based on how each species processes sensory information, which would affect their threshold for stimuli like itch. However, there isn't a singular answer across all animal species, and this field warrants detailed research on specific organisms.