Elucidating the behavior of an

05-Jun-2019 04:23 by 4 Comments

Elucidating the behavior of an

A quantitative analysis of the action impulse was successfully undertaken by Alan L. Huxley and colleagues in Cambridge (Hodgkin and Huxley, 1952abcd).

The aforementioned conventions are reflected in Equation 4.1.When a stimulus current pulse is arranged to depolarize the resting membrane of a cell to or beyond the threshold voltage, then the membrane will respond with an action impulse.An example of this is seen in Figure 2.8 in the action potential responses 3b and 4 to the transthreshold stimuli 3 and 4, respectively.This chapter describes the voltage clamp device, the experiments of Hodgkin and Huxley, the mathematical model into which their data were fitted, and the resulting simulation of a wide variety of recognized electrophysiological phenomena (activation, propagation, etc.). The Hodgkin and Huxley work is important not only for its ability to describe quantitatively both the active and the passive membrane, but for its contribution to a deeper understanding of the membrane mechanisms that underlie its electrophysiological behavior.The voltage clamp procedure was developed in 1949 separately by K. A remarkable improvement in the research of membrane electrophysiology was made by Erwin Neher and Bert Sakmann, who in 1976 published a method for the measurement of ionic currents in a single ionic channel (Neher and Sakmann, 1976).The capacitive component can be eliminated by keeping the membrane voltage constant during the measurement. Because the capacitive current, the first term on the right side of Equation 4.2, is proportional to the time derivative of the voltage, the capacitive current is zero if the derivative of the voltage is zero.

In this case the equation representing the membrane current reduces to: and the membrane current is composed solely of ionic currents.

For historical reasons, however, membrane behavior and the voltage clamp method are discussed here first, before ionic channel behavior and the patch clamp method are explored.

In order to describe the activation mechanism quantitatively, one must be able to measure selectively the flow of each constituent ion of the total membrane current.

This means that the potential can vary only with respect to the radius from the axis, and only radial currents can arise.

Furthermore, all membrane elements behave synchronously, so the entire axon membrane behaves as whole.

The total membrane current (as illustrated in Figure 4.1) satisfies Equation 3.48, which can be rewritten in the form: .

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