Where does spike collide?

A brief, all-or-none electrical event by which a neuron signals: the membrane potential rises sharply and returns within a few milliseconds, and the timing of these events forms the spike train that carries information down the axon. Hodgkin and Huxley's 1952 A quantitative description of membrane current and its application to conduction and excitation in nerve modelled the event in terms of voltage-gated sodium and potassium currents, capturing how the potential crosses threshold and then recovers. The referent is a physical voltage change in one cell, measured in millivolts against time, and what matters is its all-or-none form and its timing, not any sudden rise in a chart, a downward hit, or a protein on a virus.[1]

Unit

A neuron's all-or-none membrane voltage event, in millivolts over time

Recovery means

Central to the event: the membrane repolarises and passes through a refractory period before it can fire again

Measured by

Recorded as membrane potential over time by intracellular or extracellular electrodes, and summarised as firing rate or spike times

The surface glycoprotein a coronavirus uses to enter a host cell: it binds a receptor and drives fusion of the viral and cell membranes, and it is the S protein that studs the virion's envelope. Li's 2016 review Structure, function, and evolution of coronavirus spike proteins described its receptor-binding and fusion subunits and how their structure varies across coronaviruses. The referent is a molecule on the outside of a virus, defined by its structure and its role in entry, and it is unrelated to a neuron's firing, a jump in a series, or a hit in a game beyond the shared word.[2]

Unit

A viral envelope protein mediating receptor binding and membrane fusion

Recovery means

Not applicable

Measured by

Resolved by structural biology such as crystallography and cryo-electron microscopy, and assayed for receptor binding and fusion