Graded potentials occur in dendrites, cell bodies or axon terminals and refer to postsynaptic electrical impulses. They are called ‘graded’ because their size or amplitude is directly proportional to the strength of the triggering event. This means that 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) because Na+ channels are opened and Na+ moves into the cell, making the inside of the cell more positive compared to the outside.
A hyperpolarising graded potential is known as an inhibitory postsynaptic potential (IPSP) because the movement of ions that occur here prevent depolarisation which is characteristic of an action potential.
If graded potentials reaching the axon hillock depolarise the membrane to the threshold voltage or above, an action potential is initiated. A graded potential which is above the 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 does not trigger an action potential.
- ↑ Silverton, U.D. (2013) Neurons: Cellular and network properties, in: Volker, K. K. and Rohrer, S. A. (eds.) Human physiology 6th ed. United States of America: Pearson Education, Inc., pp. 251-253.
- ↑ Silverton, U. D. (2013) Neurons: Cellular and network properties, in : Rohrer, S. A. and Volker, K. K. (eds.) Human physiology. 6th ed. United States of America: Pearson Education, Inc., pp.251-253