Resilience of compound action potential peaks to high-frequency firing in the mouse optic nerve.

Action potential conduction in axons triggers trans-membrane ion movements, where Na enters and K leaves axons, leading to disruptions in resting trans-membrane ion gradients that must be restored for optimal axon conduction, an energy dependent process. The higher the stimulus frequency, the greater the ion movements and the resulting energy demand. In the mouse optic nerve (MON), the stimulus evoked compound action potential (CAP) displays a triple peaked profile, consistent with subpopulations of axons classified by size producing the distinct peaks.

Activity-Dependent Fluctuations in Interstitial [K]: Investigations Using Ion-Sensitive Microelectrodes.

In the course of action potential firing, all axons and neurons release K from the intra- cellular compartment into the interstitial space to counteract the depolarizing effect of Na influx, which restores the resting membrane potential. This efflux of K from axons results in K accumulation in the interstitial space, causing depolarization of the K reversal potential (E), which can prevent subsequent action potentials. To ensure optimal neuronal function, the K is buffered by astrocytes, an energy-dependent process, which acts as a sink for interstitial K, absorbing it at regions of high concentration and distributing it through the syncytium for release in distant regions.

A color-coded graphical guide to the Hodgkin and Huxley papers.

The five papers published by Hodgkin and Huxley in 1952 are seminal works in the field of physiology, earning their authors the Nobel Prize in 1963 and ushering in the era of membrane biophysics. The papers present a considerable challenge to the novice student, but this has been partly allayed by recent publications that have updated the reporting of current and voltage to reflect the modern convention and two books that describe the contents of the papers in detail. A disadvantage is that these guides contain hundreds of pages, requiring considerable time and energy on behalf of the reader.

The Nernst equation: using physico-chemical laws to steer novel experimental design.

The application of physico-chemical principles has been routinely used to explain various physiological concepts. The Nernst equation is one example of this, used to predict the potential difference created by the transmembrane ion gradient resulting from uneven ion distribution within cellular compartments and the interstitial space. This relationship remains of fundamental importance to the understanding of electrical signaling in the brain, which relies on current flow across cell membranes.