Neural accommodation

Key takeaways

Neural accommodation belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Neural accommodation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Neural accommodation from memory before moving on to harder problems.

Reference excerpt

Neural accommodation or neuronal accommodation occurs when a neuron or muscle cell is depolarised by slowly rising current (ramp depolarisation) in vitro. The Hodgkin–Huxley model also shows accommodation. Sudden depolarisation of a nerve evokes propagated action potential by activating voltage-gated fast sodium channels incorporated in the cell membrane if the depolarisation is strong enough to reach threshold. The open sodium channels allow more sodium ions 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) 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.

See also Accommodation index Action potential Anode break excitation Hodgkin–Huxley model

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 a Description in BioModels Database Hodgkin, A. L.; Huxley, A. F.; Katz, B. (April 1952). "Measurement of current-voltage relations in the membrane of the giant axon of Loligo". The Journal of Physiology. 116 (4): 424–48. doi:10.1113/jphysiol.1952.sp004716. PMC 1392219. PMID 14946712. Direct link to Hodgkin-Huxley paper #1 via PubMedCentral Hodgkin, A. L.; Huxley, A. F. (April 1952). "Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo". The Journal of Physiology. 116 (4): 449–72. doi:10.1113/jphysiol.1952.sp004717. PMC 1392213. PMID 14946713. Direct link to Hodgkin-Huxley paper #2 via PubMedCentral Hodgkin, A. L.; Huxley, A. F. (April 1952). "The components of membrane conductance in the giant axon of Loligo". The Journal of Physiology. 116 (4): 473–96. doi:10.1113/jphysiol.1952.sp004718. PMC 1392209. PMID 14946714. Direct link to Hodgkin-Huxley paper #3 via PubMedCentral Hodgkin, A. L.; Huxley, A. F. (April 1952). "The dual effect of membrane potential on sodium conductance in the giant axon of Loligo". The Journal of Physiology. 116 (4): 497–506. doi:10.1113/jphysiol.1952.sp004719. PMC 1392212. PMID 14946715. Direct link to Hodgkin-Huxley paper #4 via PubMedCentral Hodgkin, A. L.; Huxley, A. F. (August 1952). "A quantitative description of membrane current and its application to conduction and excitation in nerve". The Journal of Physiology. 117 (4): 500–44. doi:10.1113/jphysiol.1952.sp004764. PMC 1392413. PMID 12991237. Direct link to Hodgkin-Huxley paper #5 via PubMedCentral Neural Impulses: The Action Potential In Action by Garrett Neske, The Wolfram Demonstrations Project Interactive Hodgkin-Huxley model by Shimon Marom, The Wolfram Demonstrations Project 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.

Worked examples

Example 1 — a first encounter with Neural accommodation

Start with the simplest possible case. Write down what Neural accommodation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Neural accommodation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Neural accommodation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Neural accommodation

In research: Neural accommodation appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Neural accommodation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Neural accommodation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computational neuroscience, Electrophysiology, Ion channels, so understanding it makes those chapters shorter.
In everyday life: Look for Neural accommodation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Neural accommodation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Neural accommodation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Neural accommodation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Neural accommodation in simple terms?

Neural accommodation or neuronal accommodation occurs when a neuron or muscle cell is depolarised by slowly rising current (ramp depolarisation) in vitro. The Hodgkin–Huxley model also shows accommodation.

Why does Neural accommodation matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Neural accommodation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Neural accommodation.