Microelectrode arrays (MEAs) are devices contains multiple microelectrodes through which neural signals are obtained or delivered, essentially serving as neural interfaces that connect neurons to electronic circuitry. There are two general classes of MEAs: implantable MEAs, utilized in vivo, and non-implantable MEAs, utilized in vitro. Neurons and muscle cells create ion currents through their membranes when excited, causing a change in voltage between the within and therefore the outside of the cell. When recording, the electrodes on an MEA transduce the change in voltage from the environment carried by ions into currents carried by electrons (electronic currents). When stimulating, electrodes transduce electronic currents into ionic currents through the media. This triggers the voltage-gated ion channels on the membranes of the excitable cells, causing the cell to depolarize and trigger an nerve impulse if it's a neuron or a twitch if it's a muscle fiber .
The size and shape of a recorded signal depend on several factors: the character of the medium during which the cell or cells are located (e.g. the medium's electrical conductivity, capacitance, and homogeneity); the character of contact between the cells and therefore the MEA electrode (e.g. area of contact and tightness); the character of the MEA electrode itself (e.g. its geometry, impedance, and noise); the analog signal processing (e.g. the system's gain, bandwidth, and behavior outside of cutoff frequencies); and therefore the data sampling properties (e.g. rate and digital signal processing).