Electrotonic potential
Encyclopedia
In physiology, electrotonus refers to the "passive" spread of charge inside a neuron. "Passive" means that voltage-dependent changes in membrane conductance do not contribute. Neurons and other excitable cells produce two types of electrical potential. The first is a non-propagated local potential called an electrotonic potential, due to a local change in ionic conductance (e.g. synaptic or sensory that engenders a local current). When it spreads along a stretch of membrane, it becomes exponentially smaller (decrement). The second is a propagated impulse called an action potential
. Electrotonic potentials represent changes to the neuron's membrane potential
that do not lead to the generation of new current by action potentials. Neurons which are small in relation to their length, such as some neurons in the brain have only electrotonic potentials (starbust amacrine cell
s in the retina
are believed to have these properties); longer neurons utilize electrotonic potentials to trigger the action potential
.
The electrotonic potential travels via electrotonic spread, which amounts to attraction of opposite- and reflection of like-charged ions within the cell. Electrotonic potentials can sum spatially or temporally. Spatial summation is the combination of multiple sources of ion influx (multiple channels within a dendrite
, or channels within multiple dendrites), where temporal summation is a gradual increase in overall charge due to repeated influxes in the same location. Because the ionic charge enters in one location and dissipates to others, losing intensity as it spreads, electrotonic spread is a graded response. It is important to contrast this with the all-or-none propagation of the action potential
down the axon of the neuron.
Electrotonic spread is generally responsible for increasing the voltage of the soma (neuronal cell body) sufficiently to exceed threshold and trigger the action potential; its summation properties described above make it suitable for integrating input from many different sources. Such input may be depolarizing (positive charge, such as sodium) or hyperpolarizing (negative charge, such as chloride
).
Electrotonic potentials are conducted faster than action potentials, but attenuate rapidly so are unsuitable for long-distance signaling.
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
. Electrotonic potentials represent changes to the neuron's membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
that do not lead to the generation of new current by action potentials. Neurons which are small in relation to their length, such as some neurons in the brain have only electrotonic potentials (starbust amacrine cell
Amacrine cell
Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.-Overview:...
s in the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
are believed to have these properties); longer neurons utilize electrotonic potentials to trigger the action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
.
The electrotonic potential travels via electrotonic spread, which amounts to attraction of opposite- and reflection of like-charged ions within the cell. Electrotonic potentials can sum spatially or temporally. Spatial summation is the combination of multiple sources of ion influx (multiple channels within a dendrite
Dendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
, or channels within multiple dendrites), where temporal summation is a gradual increase in overall charge due to repeated influxes in the same location. Because the ionic charge enters in one location and dissipates to others, losing intensity as it spreads, electrotonic spread is a graded response. It is important to contrast this with the all-or-none propagation of the action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
down the axon of the neuron.
Electrotonic spread is generally responsible for increasing the voltage of the soma (neuronal cell body) sufficiently to exceed threshold and trigger the action potential; its summation properties described above make it suitable for integrating input from many different sources. Such input may be depolarizing (positive charge, such as sodium) or hyperpolarizing (negative charge, such as chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
).
Electrotonic potentials are conducted faster than action potentials, but attenuate rapidly so are unsuitable for long-distance signaling.