Refers to synaptic or receptor potentials that can vary in amplitude and direction. Graded potentials can be depolarizing or hyperpolarizing and do not have a threshold.

Action potential

Neuronal Action Potential - Introduction
Neuronal Action Potential - Graded Potentials versus Action Potentials

The voltage difference across a cell plasma membrane in the resting or quiescent state. It is also simply referred to as the resting potential (V_rest). The value of the resting membrane potential varies from cell to cell. Depending on the cell type, it can range from −90 mV to −20 mV.

For example, V_rest is −90 mV in skeletal and cardiac muscle cells as well as in astrocytes. In a typical neuron, V_rest is approximately −70 mV. In many non-excitable cells, V_rest ranges from −60 to −50 mV. In photoreceptors, V_rest is about −20 mV.

Resting membrane potential