Graded Potentials - occur in dendrites, cell bodies or axon terminals. Graded potential refers to the post synaptic electrical impulse. Called ‘graded’ because their size or amplitude is directly proportional to the strength of the triggering event. i.e. a large stimulus leads to the generation of a strong graded response, and a small stimulus leads to the generation of a weak graded response (they have variable strength signals).Graded potentials lose their strength as they move down the cell body.
A depolarising graded potential is known as an excitatory postsynaptic potential (EPSP) and this is because Na+ channels are opened and Na+ moves into the cell.
A hyperpolarising graded potential is known as an inhibitory postsynaptic potential (IPSP).
If graded potentials reaching the axon hillock depolarise the membrane to the threshold voltage, an Action potential is initiated.
A graded potential which is above threshold voltage is known as suprathreshold graded potential and this generates an action potential. However if a graded potential is below threshold voltage, it is known as a subthreshold graded potential and this does not trigger an action potential.