SCIENCE · INVESTIGATE AND EXPLAIN

Separate each ion’s equilibrium from zero total membrane current

An ion’s chemical gradient and the electrical potential difference jointly determine its electrochemical driving force. The equilibrium potential is the voltage at which those forces balance for that ion. A membrane permeable to several ions can have zero total current while individual ionic currents oppose one another. Electrical steady state is not necessarily thermodynamic equilibrium for every ion.

Learning outcome: Compare gB=0 with 0.5 at fixed A ratio 0.1, then change A ratio at fixed conductance. Retain both reversal potentials and both current directions; distinguish maintained gradients from equilibrium.

Starting recap

Identify neural and endocrine pathways, then separate electrochemical equilibrium, signal regeneration, synaptic conductance, receptor binding and secretion–clearance feedback using original bounded evidence.

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Try

At A ratio 0.1, EA=−60 mV. With gB=0.5 and EB=+60, V=(−60+30)/1.5=−20 mV. A outward current is 40 and B outward current −40 normalized units, so the total is zero although neither ion is individually at equilibrium.

Open the experiment

Predict

Does zero total membrane current require every ionic current to vanish?

Your prediction and reason

Experiment

Compare gB=0 with 0.5 at fixed A ratio 0.1, then change A ratio at fixed conductance. Retain both reversal potentials and both current directions; distinguish maintained gradients from equilibrium.

Separate zero total current from each ion’s equilibrium

Worked teaching model · synthetic values · Two fictional monovalent cations, Nernst factor stipulated 60 mV per decade. EA=60log 10(a), EB=60 from ratio 10. gA=1,gB=b; passive steady V=(EA+bEB)/(1+b). Maintained reservoirs, no changing gradients/capacitance or clinical electrolyte values.

Ion A outside/inside particle ratio: 0.1 ratio Ion B conductance relative to A: 0.5 relative conductance

Reset keeps your prediction, captures and practice history.

Zero net current can conceal equal opposing currents of different ions.

At each ion’s own equilibrium potential its electrical and chemical driving forces balance. Conductance-weighted steady voltage generally lies between them; maintained concentrations require an external reservoir or transport mechanism. This is not a clinical ion model.

Conditional quantities, each with its own unit
Quantity	Value	Unit
Ion A equilibrium potential	-60	mV
Ion B equilibrium potential	60	mV
Steady membrane voltage	-20	mV
A outward current	40	normalized current
B outward current	-40	normalized current
Total outward current (analytic balance)	0	normalized current

Original schematic mechanisms and invented parameters. No personal testing, electrical stimulation, hormone manipulation or clinical interpretation.

Zero net current can conceal equal opposing currents of different ions.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Identify the pathway and causal question

2. Connect structures, signals and assumptions

For a monovalent cation, the Nernst potential depends on the logarithm of outside/inside activity ratio. The original packet stipulates a factor of 60 mV per tenfold ratio, so EA=60log10(rA). Ion B has ratio 10 and EB=+60 mV. These are generic fictional ions under a fixed temperature/activity approximation, not clinical sodium or potassium concentrations.

With conductance gA=1 and gB=b, each outward current is g(V−E). Requiring their sum to vanish gives V=(EA+bEB)/(1+b). A voltage between the two reversal potentials generally drives A outward and B inward. Pumps or maintained reservoirs are required to sustain gradients over time; a passive steady calculation does not explain where those gradients originated.

The membrane’s capacitance governs transients, and channel gating changes conductance, so this algebra is not an action-potential waveform. Real permeabilities and multiple ions may require a different model. Keep concentration ratio, equilibrium voltage, conductance and current as separate quantities rather than calling any change in one “a stronger signal.”

3. Reconstruct an original worked comparison

4. Predict and investigate

Predict first: Does zero total membrane current require every ionic current to vanish?

Compare gB=0 with 0.5 at fixed A ratio 0.1, then change A ratio at fixed conductance. Retain both reversal potentials and both current directions; distinguish maintained gradients from equilibrium.

5. Discriminate a changed mechanism

Apply the mechanism to a changed boundary

At A ratio 0.1 and equal conductances, find steady voltage and individual currents.

Retain the first response, units, uncertainty and any prior feedback exposure in the notebook before comparing this public explanation.

Compare a worked response

V=0 mV; A current is +60 outward and B current −60 outward, meaning 60 inward. Net current is zero, not both individual currents.

6. Retain a nonclinical evidence defense

Preserve the first prediction, complete signal or quantity ledger, alternative mechanism and missing observation in the Anatomy and Physiology course workspace. Supplied neural and hormonal values are fictional. Do not perform stimulation, reflex testing, hormone manipulation or personal health measurements. Guided feedback is not independently assessed reasoning or actual practical competence.

Supporting anatomical mechanism, checked 30 October 2026. Original models, diagrams, explanations and exercises, not clinical data or a diagnostic decision tool.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

At A ratio 0.1 and equal conductances, find steady voltage and individual currents.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Distinguish central organization, peripheral pathways and parallel outputs Next: Compare passive spread with thresholded signal regeneration

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