page_title: Action potential
section_title: History
hierarchical_section_title: Action potential / History
caption_attribution_description: Čeština: Sodno-draselná pumpa. Model sodíko-draslíkové pumpy v jejím E2-Pi stavu. Přibližné hranice lipidové dvojvrstvy jsou označeny modře (vnitřní vrstva) a červeně (vnější vrstva). English: Ribbon diagram of the sodium–potassium pump in its E2-Pi state. The estimated boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes. فارسی: Sodium-potassium pump, E2-Pi state. Calculated hydrocarbon boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes. ગુજરાતી: બે સમાંતર સમક્ષિતિજ રેખાઓ દ્વારા દર્શાવેલા લિપિડ દ્વિસ્તરમાં સોડિયમ પોટેશિયમ પંપની કાર્ટૂન રેખાકૃતિલિપિડ દ્વીસ્તરમાં જડાયેલા પ્રોટીનનો હિસ્સો મોટે ભાગે વિરુદ્ધ સમાંતર બીટા શીટનો બનેલો હોય છે.મિશ્રત આલ્ફા-હેલિક્સ-બીટા શીટ માળખા સાથે પ્રોટીનનું મોટું અંતઃકોશિક ડોમેન પણ છે. עברית: מבנה החלבון. גבולות השכבה הליפידית הכפולה מסומנים בכחול (החלק הפונה לתוך התא) ובאדום (החלק הפונה אל מחוץ לתא). हिन्दी: Ribbon diagram of the sodium–potassium pump in its E2-Pi state. The estimated boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes. Magyar: Nátrium-kálium pumpa, E2-Pi állapotban. A lipid kettősréteg becsült szénhidrogén határvonalait belül (intracelluláris) kék vonal, kívül (extracelluláris) piros vonal jelzi. Bahasa Indonesia: Pompa sodium-potasium. ಕನ್ನಡ: Ribbon diagram of the sodium–potassium pump in its E2-Pi state. The estimated boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes. 한국어: 나트륨-칼륨 펌프의 E2-Pi형. 지질 이중층 경계 추정치를 파란색(세포 안쪽)과 빨간색(세포 바깥쪽)으로 나타냄. Lietuvių: Natrio-kalio siurblys, E2-Pi būsena. 中文: 鈉鉀泵的分子結構。.
context_page_description: In physiology, an action potential occurs when the membrane potential of a specific cell location rapidly rises and falls: this depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, endocrine cells, glomus cells, and in some plant cells.
  In neurons, action potentials play a central role in cell-to-cell communication by providing for—or with regard to saltatory conduction, assisting—the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon; these signals can then connect with other neurons at synapses, or to motor cells or glands. In other types of cells, their main function is to activate intracellular processes. In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction. In beta cells of the pancreas, they provoke release of insulin. Action potentials in neurons are also known as "nerve impulses" or "spikes", and the temporal sequence of action potentials generated by a neuron is called its "spike train".
context_section_description: The role of electricity in the nervous systems of animals was first observed in dissected frogs by Luigi Galvani, who studied it from 1791 to 1797. Galvani's results stimulated Alessandro Volta to develop the Voltaic pile—the earliest-known electric battery—with which he studied animal electricity (such as electric eels) and the physiological responses to applied direct-current voltages.
  Scientists of the 19th century studied the propagation of electrical signals in whole nerves (i.e., bundles of neurons) and demonstrated that nervous tissue was made up of cells, instead of an interconnected network of tubes (a reticulum).  Carlo Matteucci followed up Galvani's studies and demonstrated that cell membranes had a voltage across them and could produce direct current. Matteucci's work inspired the German physiologist, Emil du Bois-Reymond, who discovered the action potential in 1843. The conduction velocity of action potentials was first measured in 1850 by du Bois-Reymond's friend, Hermann von Helmholtz. To establish that nervous tissue is made up of discrete cells, the Spanish physician Santiago Ramón y Cajal and his students used a stain developed by Camillo Golgi to reveal the myriad shapes of neurons, which they rendered painstakingly.  For their discoveries, Golgi and Ramón y Cajal were awarded the 1906 Nobel Prize in Physiology. Their work resolved a long-standing controversy in the neuroanatomy of the 19th century; Golgi himself had argued for the network model of the nervous system.
  The 20th century was a significant era for electrophysiology. In 1902 and again in 1912, Julius Bernstein advanced the hypothesis that the action potential resulted from a change in the permeability of the axonal membrane to ions. Bernstein's hypothesis was confirmed by Ken Cole and Howard Curtis, who showed that membrane conductance increases during an action potential. In 1907, Louis Lapicque suggested that the action potential was generated as a threshold was crossed, what would be later shown as a product of the dynamical systems of ionic conductances. In 1949, Alan Hodgkin and Bernard Katz refined Bernstein's hypothesis by considering that the axonal membrane might have different permeabilities to different ions; in particular, they demonstrated the crucial role of the sodium permeability for the action potential. They made the first actual recording of the electrical changes across the neuronal membrane that mediate the action potential. This line of research culminated in the five 1952 papers of Hodgkin, Katz and Andrew Huxley, in which they applied the voltage clamp technique to determine the dependence of the axonal membrane's permeabilities to sodium and potassium ions on voltage and time, from which they were able to reconstruct the action potential quantitatively. Hodgkin and Huxley correlated the properties of their mathematical model with discrete ion channels that could exist in several different states, including "open", "closed", and "inactivated". Their hypotheses were confirmed in the mid-1970s and 1980s by Erwin Neher and Bert Sakmann, who developed the technique of patch clamping to examine the conductance states of individual ion channels. In the 21st century, researchers are beginning to understand the structural basis for these conductance states and for the selectivity of channels for their species of ion, through the atomic-resolution crystal structures, fluorescence distance measurements and cryo-electron microscopy studies.
  Julius Bernstein was also the first to introduce the Nernst equation for resting potential across the membrane; this was generalized by David E. Goldman to the eponymous Goldman equation in 1943. The sodium–potassium pump was identified in 1957 and its properties gradually elucidated, culminating in the determination of its atomic-resolution structure by X-ray crystallography. The crystal structures of related ionic pumps have also been solved, giving a broader view of how these molecular machines work.
caption: Ribbon diagram of the sodium–potassium pump in its E2-Pi state. The estimated boundaries of the lipid bilayer are shown as blue (intracellular) and red (extracellular) planes.
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