Summation

Summation

Adding graded potentials together to create a larger or smaller overall voltage change.

temporal summation

One neuron receives repeated stimuli close together in time, causing graded potentials to add together.

How does stimulus frequency affect graded potential amplitude?

Higher frequency → more summation → larger graded potential.

spatial summation

graded potentials from multiple inputs occurring simultaneously add together.

How does the number of simultaneous excitatory stimuli affect amplitude?

More excitatory stimuli → greater summation → larger graded potential.

How do excitatory and inhibitory stimuli summate?

They oppose each other. Excitatory potentials move the voltage toward threshold, while inhibitory potentials reduce that effect.

EPSP (Excitatory Postsynaptic Potential)

A graded potential that depolarizes the postsynaptic cell, making an action potential more likely.

IPSP (Inhibitory Postsynaptic Potential):

A graded potential that makes the postsynaptic cell less likely to reach threshold, making an action potential less likely.

Example of when EPSP and IPSP occur together

An EPSP raises the voltage by +5 mV, while an IPSP changes it by −3 mV. The net change is +2 mV toward threshold.

Why is summation important for triggering an action potential?

determines whether the combined graded potentials reach threshold and trigger an action potential.