summation (redirected from Summation Number)

summation /sum·ma·tion/ (sŭ-ma´shun) the cumulative effect of a number of stimuli applied to a muscle, nerve, or reflex arc.

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sum·ma·tion (s-mshn)

n.

The process by which multiple or repeated stimuli can produce a response in a nerve, muscle, or other part that one stimulus alone cannot produce.

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summation

Etymology: L, summa, total

1 an accumulative effect or action; a total aggregate; totality.

2 (in neurology) the concentration of a neurotransmitter at a synapse, either by increasing the frequency of nerve impulses in each fiber (temporal summation) or by increasing the number of fibers stimulated (spatial summation) , so that the threshold of the postsynaptic neuron is overcome and an impulse is transmitted. See also facilitation, def. 2.

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summation,

n the phenomenon in which similar actions of more than one drug result in a total action that may be expressed as the arithmetical sum of the effects of the individual drugs.

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summation

accumulate, add up, aggregate a series of numbers or quantities or events.

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summation of effects

a theory explaining clinical pruritus as the additive effects of pruritus from several causes which may raise the individual above the threshold, but pruritus from any single cause would be unlikely to do so.

summation gallop

see gallop rhythm.

neurological summation

physiological summation in synapses is a characteristic of the mammalian nervous system. It may be spatial, with additional synaptic junctions participating, or temporal, when succeeding stimuli catch up with the as-yet undischarged neurotransmitter. Seen in the retina of the cat, as an example of a nocturnal animal, where many millions of photoreceptors are connected to only one million axons, resulting in maximal sensitivity to light.

weighted summation

the sum obtained by adding the numerical value for individual clinical signs, each weighted to express their importance, when making a diagnosis. The total, as a fraction or a percentage, provides an estimate of the probability of each diagnosis being the correct one.

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summation 

Increased effect produced by a series of stimuli applied either simultaneously or successively (provided the intervals are greater than the latent period). Binocular summation usually occurs when the two eyes are stimulated; thus binocular brightness is greater than monocular, except in the unusual Fechner's paradox. Two or more stimuli falling within the excitatory region of a receptive field will increase the excitatory response and similarly two or more stimuli falling within the inhibitory region of a receptive field will increase the inhibition: this is called spatial summation. The summation may also occur if successive stimulations are received by the same retinal region: this is called temporal summation. See complex cell; simple cell; receptive field; lateral inhibition.