Neural accommodation or neuronal accommodation occurs when a

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

cell is depolarised by slowly rising current ( ramp depolarisation) ''in vitro''. The

Hodgkin–Huxley model 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 charact ...

also shows accommodation. Sudden depolarisation of a nerve evokes propagated

action potential 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, ...

by activating

voltage-gated Voltage-gated ion channels are a class of transmembrane proteins that form ion channels that are activated by changes in the electrical membrane potential near the channel. The membrane potential alters the conformation of the channel proteins ...

fast

sodium channels Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na+) through a cell's membrane. They belong to the superfamily of cation channels and can be classified according to the trigger that opens the channel ...

incorporated in the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

if the depolarisation is strong enough to reach threshold. The open sodium channels allow more

sodium ion Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable is ...

s to flow into the cell and resulting in further depolarisation, which will subsequently open even more sodium channels. At a certain moment this process becomes regenerative (

vicious cycle A vicious circle (or cycle) is a complex chain of events that reinforces itself through a feedback loop, with detrimental results. It is a system with no tendency toward equilibrium (social, economic, ecological, etc.), at least in the short r ...

) and results in the rapid ascending phase of action potential. In parallel with the depolarisation and sodium channel activation, the inactivation process of the sodium channels is also driven by depolarisation. Since the inactivation is much slower than the activation process, during the regenerative phase of action potential, inactivation is unable to prevent the "chain reaction"-like rapid increase in the membrane voltage. During neuronal accommodation, the slowly rising depolarisation drives the activation and inactivation, as well as the potassium gates simultaneously and never evokes action potential. Failure to evoke action potential by ramp depolarisation of any strength had been a great puzzle until Hodgkin and Huxley created their physical model of action potential. Later in their life they received a Nobel Prize for their influential discoveries. Neuronal accommodation can be explained in two ways. "First, during the passage of a constant cathodal current through the membrane, the potassium conductance and the degree of inactivation will rise, both factors raising the threshold. Secondly, the steady state ionic current at all strengths of depolarization is outward, so that an applied cathodal current which rises sufficiently slowly will never evoke a regenerative response from the membrane, and excitation will not occur." (quote from Hodgkin and Huxley) ''In vivo'' physiologic condition accommodation breaks down, that is long-duration slowly rising current excites nerve fibers at a nearly constant intensity no matter how slowly this intensity is approached.

References

External links

Interactive Java applet of the HH model
Parameters of the model can be changed as well as excitation parameters and phase space plottings of all the variables is possible.
Direct link to Hodgkin-Huxley model
and
Description
in BioModels Database * Direct link to Hodgkin-Huxley paper #1 via PubMedCentral * Direct link to Hodgkin-Huxley paper #2 via PubMedCentral * Direct link to Hodgkin-Huxley paper #3 via PubMedCentral * Direct link to Hodgkin-Huxley paper #4 via PubMedCentral * Direct link to Hodgkin-Huxley paper #5 via PubMedCentral
Neural Impulses: The Action Potential In Action
by Garrett Neske,

The Wolfram Demonstrations Project The Wolfram Demonstrations Project is an organized, open-source collection of small (or medium-size) interactive programs called Demonstrations, which are meant to visually and interactively represent ideas from a range of fields. It is hos ...

Interactive Hodgkin-Huxley model
by Shimon Marom,

ModelDB
A computational neuroscience source code database containing 4 versions (in different simulators) of the original Hodgkin–Huxley model and hundreds of models that apply the Hodgkin–Huxley model to other channels in many electrically excitable cell types. {{DEFAULTSORT:Hodgkin-Huxley Model Nonlinear systems Electrophysiology Ion channels Computational neuroscience

See also

References

External links