Graded potential

 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. This graded potentials will lose it strength and consequently, die out within 1-2mm from the their origins. Summation of graded potentials is possible that may generate action potential.

Graded potential may be a depolarising one or a hyperpolarising one. A depolarising local response will cause the membrane potential to be less negative thus, brings it closer to the treshold value to generate an action potental. This response increases the excitability of the cell. Meanwhile, a hyperpolarising local response has a vice versus effect towards the membrane potential value. It will make the inside of the membrane becomes more negative and therefore, reduce its excitibility.

The depolarising event may occur due to the inwards movement of positively-charged ions, such as sodium ions (Na⁺) to the cell, or the outwards movement of negatively-charged ions from the cell. The hyperpolarising local potential can arise due to either the negative anions, such as chloride ions (Cl^-) enter the cell or the positive cations exit from the cell.

 
A depolarising graded potential is known as an excitatory postsynaptic potential (EPSP).

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.

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