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1. the act or process of determining a sum; addition
2. the result of such an act or process
3. US law the concluding statements made by opposing counsel in a case before a court



in physiology, the cumulative effect of several stimuli following one another in rapid succession (temporal summation) or occurring simultaneously (spatial summation) and arising in such excitable structures as receptors, neurons, and muscles.

Summation was first described in 1868 by I. M. Sechenov, who observed that under certain conditions of rhythmic stimulation there was a delay in the appearance and subsequent intensification of reflexes. Temporal summation occurs in the intervals between stimuli. These intervals are limited by the period of subthreshold or trace shifts in membrane potential toward depolarization, with development of excitation, or toward hyper-polarization, with development of inhibition. Temporal summation ensures that the duration of the reaction will be sufficient and that it can be maintained by the circular relationship between the neurons.

Spatial summation changes continuously and is manifested by the simultaneous excitation or inhibition of many neurons in different parts of the brain as well as of numerous synapses in a single neuron. Summation helps to intensify individual reactions and to coordinate the body’s reactions. In muscles, spatial summation intensifies contractions by increasing the number of excited motor units, that is, groups of fibers innervated by a single neuron. Temporal summation in muscles induces tetanus by uniting successive individual contractions.


References in periodicals archive ?
Specifically, Figure 8(a) shows that at w = 3, the smallest weighted summation of the type I and type II errors with cost vector [c.sub.1] is approximately 0.57, which is achieved at {8, 14, 17} when combining the 8th, 14th, and 17th windows out of the twenty 24-hour windows prior to a decision time.
The fuzzy weighted summations of the positive distance and negative distances from average matrix using equal criteria weights are as follows:
The reason is that the similarity computation for a node in a query tree may be based on operators other than a weighted summation of the similarity of the children.
A closer look in the last equation reveals that now W takes the more meaningful form of a weighted summation over the second sample of the observed number of failures [d.sub.2j] minus the conditionally expected ones [n.sub.2j][d.sub.cj]/[n.sub.cj].
At the FC, the final decision is made by comparing the weighted summation of local observed energies with a decision threshold, in which the weight of a local observed energy is determined by normalizing the corresponding SNR.

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