Summation - defined, spatial, temporal & AP generation or not

If several presynaptic end bulbs release their neurotransmitter at about the same time, the combined effect may generate a nerve impulse due to summation Summation may be spatial or temporal • A typical neuron may have thousands of synapses. A corresponding number of postsynaptic membrane potentials will be integrated and summed at its trigger zone. • The sum of potentials from multiple synapses of presynaptic neurons is called spatial summation. • The sum of potentials coming from only one synapse, but multiple times in succession is called temporal summation. • Summation of graded potentials will determine whether or not an action potential is generated. • If the sum of IPSPs and EPSPs results in a hyperpolarization, no action potential generated. • If the sum of IPSPs and EPSPs results in a sub threshold depolarization, no action potential is generated. • If the sum of IPSPs and EPSPs results in an above-threshold depolarization, an action potential is generated.

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