Neuroscience / electrophysiology · BEGINNER LESSON
Input resistance
Input resistance is a measure of how much a neuron's membrane voltage changes when a current is injected. It is calculated as R_input = ΔV / I, where ΔV is the voltage change and I is the injected current.
What it is and what is measured
Input resistance is a biophysical property of a neuron’s membrane. It tells how large the change in membrane potential becomes after a known current is injected. In the cited study, it was measured as R_input = ΔV / I using a -100 pA current injection, where ΔV means change in membrane potential and I means current. A higher value means the same input produces a larger voltage change, which can make spike generation easier.
[1] Input-Specific Organization of Intrinsic Excitability Expands Coding ... [2] Table 9.
How it affects firing
The sources connect input resistance to intrinsic excitability, meaning how likely a neuron is to generate action potentials when stimulated. Neurons with higher input resistance showed greater input–output gain and were more easily driven toward threshold for spiking. In mature MNTB neurons, input resistance helped distinguish phasic firing cells, which fire briefly, from tonic firing cells, which can fire more continuously. The study also reports that tonic cells had higher input resistance and slower membrane time constant, τm, than phasic cells.
[1] Input-Specific Organization of Intrinsic Excitability Expands Coding ...
What likely sets it
The main mechanism described is resting potassium conductance, especially leak potassium channel density. Leak conductance is the constant passage of ions through channels open at rest. More leak conductance lowers input resistance because current can escape more easily across the membrane; less leak conductance raises input resistance. The authors conclude that postsynaptic resting potassium conductance is calibrated to match the strength of presynaptic input and help diversify excitation-spike coupling fidelity.
[1] Input-Specific Organization of Intrinsic Excitability Expands Coding ... [2] Table 9.
Limitations and interpretation
Input resistance is not the same as resting membrane potential, because the study reports that resting membrane potential could be similar even when input resistance differed. It is also not a direct count of synapses or a direct measure of action potential shape. It is one part of a broader electrical profile that includes τm and potassium conductance, so it should be interpreted together with other membrane properties rather than alone.
[1] Input-Specific Organization of Intrinsic Excitability Expands Coding ... [2] Table 9.
SEE THE IDEA
How input resistance shapes neuronal response
A known current is applied to the cell to test its voltage response.
Higher R_input means a larger voltage change for the same current.
Larger voltage changes can make threshold for spiking easier to reach.
Current applied to the membrane produces a voltage change; the size of that change determines input resistance and helps shape whether spikes occur.
A simple chain from test current to voltage change to spike likelihood.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.