Summation

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Summation at Synapses Finely Tunes the Nervous Res

If a stimulus is weak, only a small amount of neurotransmitter will be released from a neurone into the synaptic cleft. This might not be enough to excite the postsynaptic membrane to the threshold level and stimulate an action potential. Summation is where the effect of neurotransmitter released from many neurones (or one neurone that is stimulated a lot in a short period of time) is added together. There are two types of summation:

Temporal Summation and

Spatial Summation

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Temporal Summation

Temporal summation is where two or more nerve impulses arrive in quick succession from the same presynaptic neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.

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Spatial Summation

Sometimes many neurones connect to one neurone. The small amount of neurotransmitter released from each of these neurones can be enough altogether to trigger an action potential. If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential.

Both types of summation mean synapses accurately process information, finely tuning the response.

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