hyperpolarizing graded potential and depolarizing graded potential

When action potentials fire simultaneously in several neurons that weakly synapse on a single cell, they may initiate an impulse in that cell even though the synapses are weak. This process is known as summation.

Temporal summation is an effect generated by a single neuron as a way of achieving action potential.

Spatial summation is a way of achieving action potential in a neuron which involves input from multiple cells.

Remember:  ALL action potentials fired by single neuron look the same (in terms of amplitude and duration), even if the stimulus intensities vary!  Any time a neuron reaches threshold, APs will be fired.  The rate at which they are fired may vary based on the stimulus intensity— for examepl: a neuron will fire more APs per unit time (FREQUENCY) given a stimulus of greater intensity-- but each individual action potential should be identical!  This is due to a neuron’s v-gated channels, which are triggered to open and close at certain voltages!