what did hodgkin and huxley do

In 1952, Hodgkin and Huxley

wrote a series of five papers that described the experiments they conducted that were aimed at determining the laws that govern the movement of ions in a nerve cell during an action potential.

Full Answer

What is the Hodgkin Huxley model?

Hodgkin-Huxley Models. The core mathematical framework for modern biophysically based neural modeling was developed half a century ago by Sir Alan Hodgkin and Sir Andrew Huxley. They carried out an elegant series of electrophysiological experiments on the squid giant axon in the late 1940s and early 1950s.

Who were Alan Hodgkin and Andrew Huxley?

Alan Hodgkin and Andrew Huxley were two English physiologists who pioneered some of the first experiments into modeling the function and behavior of neurons using electrophysiology.

What did Hodgkin and Huxley learn from the giant squid axon?

What did Hodgkin and Huxley learn from the giant squid axon? Answer: They developed a model to explain the ionic conductances observed during initiation and conduction of the action potential.

What is the Huxley model of action potentials?

Alan Hodgkin and Andrew Huxley described the model in 1952 to explain the ionic mechanisms underlying the initiation and propagation of action potentials in the squid giant axon. They received the 1963 Nobel Prize in Physiology or Medicine for this work.

What information did the Hodgkin and Huxley model provide?

The Hodgkin–Huxley model, or conductance-based model, is a mathematical model that describes how action potentials in neurons are initiated and propagated. It is a set of nonlinear differential equations that approximates the electrical characteristics of excitable cells such as neurons and muscle cells.

What did Hodgkin and Huxley Discover 1939?

Finally, Hodgkin, Huxley and Katz (following Cole and Marmont) developed a voltage-clamp circuit to enable quantitative measurement of ionic currents from squid axon.

What was Hodgkin and Huxley's achievement?

Hodgkin and Huxley were able to use Equation (6) to predict the time-course, the size of the displacement in , and many of the finer features of the action potential with striking accuracy.

Why is the Hodgkin Huxley model important?

Abstract. Hodgkin and Huxley (H-H) model for action potential generation has held firm for half a century because this relatively simple and experimentally testable model embodies the major features of membrane nonlinearity: namely, voltage-dependent ionic currents that activate and inactivate in time.

How did Hodgkin and Huxley investigate action potential?

Hodgkin and Huxley got around this problem by studying action potentials in the relatively enormous axons (up to 1 mm in diameter) of the squid. They inserted a fine capillary electrode into the squid giant axon and were able to measure electrical changes within the axon during an action potential.

What is the strength of Hodgkin Huxley model?

The Hodgkin-Huxley model is stimulated by a short, but strong, current pulse between t=1 and t=2 ms. The time course of the membrane potential u(t) for t>2ms shows the action potential (positive peak) followed by a relative refractory period where the potential is below the resting potential urest (dashed line).

Who discovered action potential?

Julius BernsteinJulius Bernstein, with the help of Emil du Bois-Reymond, found a way to overcome these technical limitations and in about 1865 made the first recordings of the time course of the action potential.

Who discovered the voltage clamp?

Kenneth ColeIn the late 1940s, at the University of Chicago, Kenneth Cole, with the help of George Marmont, invented an electronic circuit called a voltage clamp,2 which was used to investigate ionic conduction in nerves.

Why do squid have giant axons?

The giant axon of the squid is the largest known nerve cell in the animal kingdom. They can be up to 1mm in diameter and almost a metre long. The axon is part of the squid's propulsion system, and runs from the ganglion to muscles carrying signals which control and co-ordinate movement.

Why did Hodgkin and Huxley use squid?

Hodgkin and Huxley chose the giant squid axon as a model system for their experiments, since it is unusually large (around 0.5 mm in diameter) and therefore quite suitable for electrophysiological experiments [1].

What method did Hodgkin and Huxley invent in order to determine the ionic currents that mediated the action potential?

voltage-clamp techniqueThe sodium current that initiates the nerve action potential was discovered by Hodgkin and Huxley using the voltage-clamp technique in their landmark series of papers in 1952.

Who discovered ion channels?

The existence of ion channels was confirmed in the 1970s by Bernard Katz and Ricardo Miledi using noise analysis. It was then shown more directly with an electrical recording technique known as the "patch clamp", which led to a Nobel Prize to Erwin Neher and Bert Sakmann, the technique's inventors.

Who was Alan Hodgkin and Andrew Huxley?

Working together in 1939, and again from 1946 to 1952, Alan Hodgkin and Andrew Huxley formed one of the most productive and influential collaborations in the history of physiology.

Who discovered Hodgkin lymphoma?

Hodgkin Lymphoma (HL) Thomas Hodgkin who, in 1832, described several cases of people with symptoms of a cancer involving the lymph nodes. The disease was called "Hodgkin's disease" until it was officially renamed "Hodgkin lymphoma" in the late 20th century.

What is an action potential?

To understand Hodgkin and Huxley's findings, it helps to have some background on what happens during an action potential. When a neuron is at rest, there are a variety of charged particles called ions that are unevenly distributed inside and outside of the cell.

Voltage clamps and squid axons

One of the difficulties in understanding action potentials before Hodgkin and Huxley's work was that neurons are incredibly small. (At their largest they are about 100 micrometers, but they can be under 10 micrometers.

Which two scientists used the squid giant axon to develop their mathematical model of conduction?

Although both sets of experiments were valuable, the squid giant axon studies allowed Hodgkin and Huxley to develop their mathematical model of conduction across a membrane.

Who were the two scientists who discovered the function of neurons?

Alan Hodgkin and Andrew Huxley were two English physiologists who pioneered some of the first experiments into modeling the function and behavior of neurons using electrophysiology. They initially worked collaboratively at the Physiological Laboratory (Cambridge) in 1935 using the frog sciatic nerve model, and later at the Laboratory of the Marine Biological Association (Plymouth) using the squid giant axon.

What was the impact of Hodgkin and Huxley's work?

The effect of Hodgkin and Huxley's work was tremendous, leading to an explosion of interest in electrophysiology. The voltage-clamp technique began to be used on a range of large cells. However, it was Neher and Sakmann's development of the patch-clamp in the 1970s that allowed the first recordings of single ion channels from even the smallest of cells. Such recordings of these small currents were impossible using the valve-based amplifiers of 1949, and equally they would not have been possible in the 1970s without Hodgkin and Huxley's pioneering work. However, the impact of their work extended well beyond experimental electrophysiology. The Hodgkin–Huxley model contained within it probabilistic representations of the activation and inactivation of ionic conductances. In 1955 Hodgkin and Keynes published data that predicted that K + channels would be occupied by multiple ions simultaneously ( Hodgkin & Keynes, 1955 ). The molecular structural description of K + channels, confirming this prediction, won Rod MacKinnon the 2003 Nobel prize in Chemistry (see Fig. 5 ). Indeed, the ideas and equations behind their model are now the standard building blocks of neuronal modelling software for both teaching and research.

What did Huxley do in 1939?

2 ). Eventually in August 1939, after weeks of waiting, the trawlers operating beyond Plymouth Sound began to bring in catches of squid.

Why are two views of the same axon visible?

This allowed simultaneous viewing of the electrode from both front and side and was essential to avoid the electrode damaging the nerve membrane as it was threaded down the axon. Image taken from Hodgkin & Huxley (1945).

How did Huxley measure the viscosity of the axoplasm?

Huxley started by trying to measure the viscosity of axoplasm by observing the passage of mercury droplets through it , but the experiments were not a great success ( Huxley, 2004 ). The droplets sat obstinately at the top of cut axons, descending only if the axoplasm was damaged.

How many currents are there in Hodgkin's model?

Hodgkin and Huxley thus emerged with a model which incorporated four currents (capacitance, K +, Na + and leak). These, when iteratively summed to give a total current, I, predict the action potential time course with remarkable accuracy. The three voltage- and time-dependent, but otherwise uncoupled ‘variables’ ( n, m and h ), which define the proportion of the K + and Na + channels available as a proportion of the maximum available conductance ( and ) at any given time within the trajectory of an action potential, underlie the model's elegance.

Who discovered the squid giant axon?

J. Z. Young, squid and the Marine Biological Association (MBA) A, John Zachary Young (1907–1997). His discovery of the squid giant axon in the 1930s was pivotal since it provided an electrically excitable membrane of sufficient area for Hodgkin and Huxley's experiments.

Who was the scientist who worked on the squid giant axons?

In the 1950s Alan Hodgkin' s interest in the squid giant axons continued with work on calcium and the sodium pump. Andrew Huxley, however, had moved his attention to the mechanisms of activation of skeletal muscle contraction. Whilst they did not collaborate again, they both continued to make substantial individual contributions to physiology.

How does the HH model work?

Each individual ion channel can be thought of as containing one or more physical gates that regulate the flow of ions through the channel. An individual gate can be in one of two states, permissive or non-permissive. When all of the gates for a particular channel are in the permissive state, ions can pass through the channel and the channel is open. If any of the gates are in the non-permissive state, ions cannot flow and the channel is closed. Although it might seem more natural to speak of gates as being open or closed, a great deal of confusion can be avoided by consistently using the terminology permissive and non-permissive for gates while reserving the terms open and closed for channels.

Who developed neural modeling?

The core mathematical framework for modern biophysically based neural modeling was developed half a century ago by Sir Alan Hodgkin and Sir Andrew Huxley. They carried out an elegant series of electrophysiological experiments on the squid giant axon in the late 1940s and early 1950s. The squid giant axon is notable for its extraordinarily large diameter (~0.5 mm). Most axons in the squid nervous system and in other nervous systems are typically at least 100 times thinner. The large size of the squid giant axon is a specialization for rapid conduction of action potentials that trigger the contraction of the squid’s mantle when escaping from a predator. In addition to being beneficial for the squid, the large diameter of the giant axon was beneficial for Hodgkin and Huxley because it permitted manipulations that were not technically feasible in smaller axons that had been used in biophysical studies up to that point. In a well-designed series of experiments, Hodgkin and Huxley systematically demonstrated how the macroscopic ionic currents in the squid giant axon could be understood in terms of changes in Na+ and K+ conductances in the axon membrane. Based on a series of voltage-clamp experiments, they developed a detailed mathematical model of the voltage-dependent and time-dependent properties of the Na+ and K+ conductances. The empirical work lead to the development of a coupled set of differential equations describing the ionic basis of the action potential (Hodgkin and Huxley, 1952), which became known as the Hodgkin-Huxley (HH) model. The real predictive power of the model became evident when Hodgkin and Huxley demonstrated that numerical integration of these differential equations (using a hand-cranked mechanical calculator!) could accurately reproduce all the key biophysical properties of the action potential. For this outstanding achievement, Hodgkin and Huxley were awarded the 1963 Nobel Prize in Physiology and Medicine (shared with Sir John Eccles for his work on the biophysical basis of synaptic transmission).

Andrew Fielding Huxley

The Nobel Prize in Physiology or Medicine 1963 was awarded jointly to Sir John Carew Eccles, Alan Lloyd Hodgkin and Andrew Fielding Huxley "for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane."

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Overview

Basic components

Ionic current characterization

Mathematical properties

Improvements and alternative models

See also

Further reading

External links