Mid: The input value that produces output mid way up the curve of the sigmoid shape.Two parameters control the shape of the sigmoid: Sigmoid: The function has a sigmoid shape varying between the minimum and maximum. Y = min + (max - min) \times (x - thresh) / (sat - thresh) Saturate: Above this input level, the output is the maximum.įor input between the threshold and saturate levels, the output scales linearly:.Threshold: Below this input level, the output is the minimum.Linear: There is linear interpolation between the minimum and maximum. In each case there may be a specified minimum and maximum output. Many transfer functions of the form y = f( x) allow the user to choose between linear, sigmoid, and user-specified types. By careful manipulation the channel can be arranged to have its inner surface within the electrode lumen (outside-out patch) or its outer surface within the lumen (inside-out patch). Current flowing through the channels can be recorded, and the chemical environment on both sides of the channel can be controlled by the experimenter. As c, but the electrode is withdrawn from the cell, bringing the single channel with it. This can record the current through that channel, with the rest of the cell still attached and undamaged. A patch electrode attaches to the cell surface with just a single ion channel under its tip. Also a patch electrode is usually blunter than a sharp electrode, and passes current more easily and records with less noise. This can record and stimulate like method a, but usually causes less damage to the cell. A patch electrode attaches to the cell surface and breaks the membrane just under its tip. This can record the membrane potential or inject current. A sharp microelectrode penetrates into the interior of the cell. The blunt end of the tube is connected by a wire to a recording amplifier or stimulator. Intracellular recording usually involves a microelectrode - a glass tube drawn out to a very fine point and filled with an electrolyte.
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