Specifications

MEA-System Manual

3 Extracellular Recording from MEAs

3.1 Introduction

Over the last 30 years, non-invasive extracellular recording from multiple electrodes has

developed into a widely used standard method. Systems and methods have been greatly

improved, leading to more features, higher throughput, and lower costs. Almost all excitable or

electrogenic cells and tissues can be used for extracellular recording in vitro, for example, central

or peripheral neurons, heart cells, retina, or muscle cells.

3.2 Background

The semi permeable lipid bilayer cell membrane separates different ion concentrations (charges)

on the inner and outer side of the membrane. Therefore, the cell membrane has the electrical

properties of a plate capacitor. The electrochemical gradient results in a membrane potential that

can be measured directly with an intracellular electrode. When ion channels are opened due to

chemical or electrical stimulation, the corresponding ions are moving along their electrochemical

gradient. In other words, the resistance of the membrane is lowered, resulting in an inward or

outward flow of ions, measured as a transmembrane current.

The extracellular space is conductive as well, and though the resistance is very low, it is not zero.

According to Ohm's law (U=R*I), the extracellular current results in a small voltage that can be

measured with extracellular electrodes. Extracellular signals are smaller than transmembrane

potentials, depending on the distance of the signal source to the electrode. Extracellular signal

amplitudes decrease with increasing distance of the signal source to the electrode. Therefore, a

close interface between electrode and cell membrane is very important for a high signal-to-noise

ratio.

The transmembrane current and the extracellular potential follow the same time course and are

roughly equal to the first derivative of the transmembrane potential.

A microelectrode array (MEA) is an arrangement of several (typically 60) electrodes allowing

targeting several sites for stimulation or recording at once.

The following components are important for an extracellular recording system:

 Signal source (cells / tissue)

 Cell / sensor interface

 Biosensor (MEA)

 Filter amplifier (MEA1060)

 Recording hardware (MC_Card) and software (MC_Rack)