Electrophysiology

electrophysiology studies the electrochemical characteristics of the living organisms.

Production of electric current by the alive one

Electric potential of membrane

The basic unit of alive, the cell, has the characteristic to have a negative polarization compared to outside. The phospholipidic membrane is insulator electrical placed between two conducting aqueous mediums. She thus plays the condensing part of electric. The existence of channels Potassium opened with at-rest state allows the chemical gradient these ions, maintained by the Na/K ATPase, to dissipate itself. The exit of Ion S potassium creates a microphone-separation of load on the surface of the membrane. This separation of load is a potential difference electric, the interior of the cell becoming negative compared to outside. This negative value is opposed to the exit ions potassium.

Thus, to summarize, the potential of membrane is created by the concomitant existence of two phenomena.

an ionic imbalance is maintained by the membrane pumps, in particular Na/K ATPase which exchanges ions Sodium against ions potassium. This exchange is done against the chemical gradient of these species and thus requires energy, provided in the form of ATP.
the opening to at-rest state of the potassic channels makes it possible the chemical gradient of this ion to be dissipated by a phenomenon of diffusion. This exit of ions potassium creates a potential difference, polarizing the interior of the cell negatively compared to outside.

Cells excitables

Certain specialized cells have the capacity to be depolarized brutally when their potential of membrane was depolarized beyond of a value threshold. This explosive depolarization is followed of a repolarization. It is about a Potentiel of action. It utilizes the opening and the closing of ionic channels depend on the permeable potential of membrane either to sodium or calcium (they allow depolarization), or with potassium (they allow the repolarization which goes sometimes until a light hyperpolarisation).

The cells excitables are:

the Neuron S or nervous cells
the Myocyte cardiac S or muscular cells
the striated skeletal muscular cells

particular case of the electric Body of Torpedo…

Balance maintains osmotic

operation of the Kidney, " turgescence " vegetable cells…

Energy production

In end of the bioenergetic chain, as well in the Mitochondrion S as in the Chloroplast S, a flow of protons through ATP synthétase allows the synthesis of ATP.

Electrophysiological methods

Electrophysiology consists in measuring ion flows on both sides of a biological membrane.

One of the first experiments of electrophysiology was carried out by Luigi Galvani, which described the animal electricity (obsolete term). Whereas it dissected a Grenouille, it realized that the contact between the metal of its scalpel and the Nerf sciatic nerve of the animal caused muscular contractions. It showed that the scalpel was not " actif" that if it were in charge of static electricity. It from of deduced that electric phenomena controlled the contraction of the muscles.

neurons with the potentials of action…

technique of empalement…

technique of the patch-clamp…

The techniques of Patch-clamp in addition make it possible to measure the electric currents on the level of a cell, or even of a piece of membrane, and until a resolution making it possible to measure the activity of only one molecule channel.

One can measure the field of potential generated by a large population of synchronized neurons, which is the case for bodies like the Cœur (electrocardiogram ECG) or the brain (electroencephalogram EEG). This is done by direct affixing of electrode on the skin of the patients.

Other methods are complementary to electrophysiology. For example, of the techniques of not-invasive imageries use the indirect effects of the electric activity of the neurons to follow the cerebral activity (the methods of electrophysiology allow, they, of direct measurements). Tomography by positon, for example, measurement accelerations of blood flows which are nearly simultaneous with the activation of groups of neurons. Indeed, when a neuron discharges from the potentials of action, there is an increase in consumption in Glucose, accompanied by an increase in blood circulation. The tomography allows the visualization of the cerebral zones where the consumption of glucose by the cells is most important, and consequently, of the most active zones of the brain.

See too

History of electrophysiology
List of ionic currents (neuroscience)

External bonds

Manual of Electrophysiology: '' Foudations off electrophysiology '' (contents)

Simple: Electrophysiology

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