Electric organ
Encyclopedia
In biology
, the electric organ is an organ common to all electric fish
used for the purposes of creating an electric field
. The electric organ is derived from modified nerve or muscle tissue. The electric discharge from this organ is used for navigation, communication, defence and also sometimes for the incapacitation of prey.
papers by Hunter, Walsh and Williamson, and they appear to have influenced the thinking of Luigi Galvani
and Alessandro Volta
, the founders of electrophysiology and electrochemistry.
In the 19th Century, Charles Darwin
, in Origin of Species discussed the electric organ as a likely example of convergent evolution
: "But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other…I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection
, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings".
In the 20th Century, electric organs have received extensive study, for example Lissman's 1951 paper and his review of their function and evolution in 1958.
used by ray
s, electric eel
s and other electric fish
for electrogenesis. They are flat disk-like cells. Electric eels have several thousand of these cells stacked, each producing 0.15V. The cells function by pumping positive sodium
and potassium
ions out of the cell via transport proteins powered by ATP
. Postsynaptically, electrocytes work much like muscle cells. They have nicotinic acetylcholine receptor
s. These cells are used in research because of their resemblance to nerve-muscle junctions.
The stack of electrocytes has long been compared to a voltaic pile
, and may even have inspired the invention of the battery
, since the analogy was already noted by Alessandro Volta
. While the electric organ is structurally similar to a battery, its cycle of operation is more like a Marx generator
, in that the individual elements are slowly charged in parallel, then suddenly and nearly simultaneously discharged in series
to produce a high voltage pulse.
, a nucleus
of pacemaker neuron
s. When an electric eel spots its prey, the pacemaker neurons fire and acetylcholine
is subsequently released from electromotor neurons to the electrocytes, resulting in an electric organ discharge.
s and in rays they are oriented along the dorso-ventral(up-down) axis. In most fishes, the organs lie along the length of the tail within the musculature. Many of them have smaller accessory electric organs in the head. In the electric Torpedo Ray, the organ is near the pectoral muscles and the gills(see the image). The stargazer's electric organs lie between the mouth and the eye. In the electric catfish, the organs are located just below the skin and encase most of the body like a sheath.
Phylogeny of weakly electric fishes.
Comprehensive overview of electric organ function and evolution in weakly electric fishes.
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, the electric organ is an organ common to all electric fish
Electric fish
An electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the sea and in freshwater...
used for the purposes of creating an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
. The electric organ is derived from modified nerve or muscle tissue. The electric discharge from this organ is used for navigation, communication, defence and also sometimes for the incapacitation of prey.
Research History
In the 1770s the electric organs of the torpedo and electric eel were already the subject of Royal societyRoyal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
papers by Hunter, Walsh and Williamson, and they appear to have influenced the thinking of Luigi Galvani
Luigi Galvani
Luigi Aloisio Galvani was an Italian physician and physicist who lived and died in Bologna. In 1791, he discovered that the muscles of dead frogs legs twitched when struck by a spark...
and Alessandro Volta
Alessandro Volta
Count Alessandro Giuseppe Antonio Anastasio Gerolamo Umberto Volta was a Lombard physicist known especially for the invention of the battery in 1800.-Early life and works:...
, the founders of electrophysiology and electrochemistry.
In the 19th Century, Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
, in Origin of Species discussed the electric organ as a likely example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
: "But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other…I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings".
In the 20th Century, electric organs have received extensive study, for example Lissman's 1951 paper and his review of their function and evolution in 1958.
Electrocytes
Electrocytes, electroplaques or electroplaxes are cellsCell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
used by ray
Electric ray
The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, comprising the order Torpediniformes. They are known for being capable of producing an electric discharge, ranging from as little as 8 volts up to 220 volts depending on species, used to stun prey and...
s, electric eel
Electric eel
The electric eel , is an electric fish, and the only species of the genus Electrophorus. It is capable of generating powerful electric shocks, of up to six hundred volts, which it uses for both hunting and self-defense. It is an apex predator in its South American range...
s and other electric fish
Electric fish
An electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive. Electric fish species can be found both in the sea and in freshwater...
for electrogenesis. They are flat disk-like cells. Electric eels have several thousand of these cells stacked, each producing 0.15V. The cells function by pumping positive sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
ions out of the cell via transport proteins powered by ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
. Postsynaptically, electrocytes work much like muscle cells. They have nicotinic acetylcholine receptor
Nicotinic acetylcholine receptor
Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...
s. These cells are used in research because of their resemblance to nerve-muscle junctions.
The stack of electrocytes has long been compared to a voltaic pile
Voltaic pile
A voltaic pile is a set of individual Galvanic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first electric battery...
, and may even have inspired the invention of the battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, since the analogy was already noted by Alessandro Volta
Alessandro Volta
Count Alessandro Giuseppe Antonio Anastasio Gerolamo Umberto Volta was a Lombard physicist known especially for the invention of the battery in 1800.-Early life and works:...
. While the electric organ is structurally similar to a battery, its cycle of operation is more like a Marx generator
Marx generator
A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse. Marx generators are often used to simulate the effects of lightning on power line gear and aviation equipment....
, in that the individual elements are slowly charged in parallel, then suddenly and nearly simultaneously discharged in series
Series and parallel circuits
Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the...
to produce a high voltage pulse.
Firing
To discharge the electrocytes at the correct time, the electric eel uses its pacemaker nucleusMedullary command nucleus
The medullary command nucleus , also called the pacemaker nucleus, is a group of nerve cells found in the bodies of weakly electric fish. It controls the function of electrocytes by regulating the frequency of electrical impulses. Signals originating in the MCN are transmitted to electrocytes,...
, a nucleus
Nucleus (neuroanatomy)
In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up...
of pacemaker neuron
Medullary command nucleus
The medullary command nucleus , also called the pacemaker nucleus, is a group of nerve cells found in the bodies of weakly electric fish. It controls the function of electrocytes by regulating the frequency of electrical impulses. Signals originating in the MCN are transmitted to electrocytes,...
s. When an electric eel spots its prey, the pacemaker neurons fire and acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
is subsequently released from electromotor neurons to the electrocytes, resulting in an electric organ discharge.
Location
The electric organs are usually oriented to fire along the length of the body in most fishes. In stargazerStargazer
The stargazers are a family Uranoscopidae of perciform fish that have eyes on top of their heads . The family includes about 50 species in 8 genera, all marine and found worldwide in shallow waters....
s and in rays they are oriented along the dorso-ventral(up-down) axis. In most fishes, the organs lie along the length of the tail within the musculature. Many of them have smaller accessory electric organs in the head. In the electric Torpedo Ray, the organ is near the pectoral muscles and the gills(see the image). The stargazer's electric organs lie between the mouth and the eye. In the electric catfish, the organs are located just below the skin and encase most of the body like a sheath.
Electric Organ Discharge
Electric organ discharge (EOD) is the electric discharge generated by the organs of animals including electric fish. In some cases the electric discharge is strong and is used for protection from predators; in other cases it is weak and it is used for navigation and communication.Further Peer-Reviewed Reading
Review Article on the molecular evolution of the electric organ.Phylogeny of weakly electric fishes.
Comprehensive overview of electric organ function and evolution in weakly electric fishes.