Separate synaptic current from depolarization and spiking

1. Identify the pathway and causal question

Synapses can change membrane conductance through ligand-gated channels or slower signaling pathways. The postsynaptic effect depends on the channel’s reversal potential and the membrane state, not only the transmitter’s name. Spatial and temporal summation combine inputs, while electrical synapses and chemical synapses have different transmission mechanisms.

2. Connect structures, signals and assumptions

A conductance with reversal near resting voltage can reduce the voltage effect of another input without producing a large resting hyperpolarization. This shunting effect lowers input resistance. Inhibition therefore need not mean that the voltage simply becomes more negative in every comparison; what matters is how the input changes the cell’s response under specified conditions.

The original steady model has leak conductance 1 at reversal −60 mV, excitatory conductance a at reversal 0, and shunting conductance b at reversal −60. Voltage is −60(1+b)/(1+a+b). The excitatory inward current magnitude is a(0−V), while leak plus shunt carries an equal outward current. These supplied reversals and conductances do not encode actual drug or transmitter concentrations.

Adding shunt can make the voltage less depolarized while increasing excitatory current because the excitatory driving force grows. Current and voltage are therefore not interchangeable evidence. Spiking, timing, dendritic geometry and receptor kinetics are omitted; this static comparison cannot determine a real neuron’s firing or diagnose a condition.

3. Reconstruct an original worked comparison

At excitatory conductance 1 and shunt 2, total conductance is 4 and V=−45 mV, a 15 mV depolarization. Excitatory inward current is 45, balanced by outward current3×15=45. Without shunt, V=−30 and excitatory current30: less voltage change can coexist with more current.

4. Predict and investigate

Predict first: Can adding a resting-reversal shunt reduce depolarization while increasing excitatory current?

Compare shunt 0 and2 at excitation 1, then set excitation 0 at both shunts. Retain voltage, total conductance and both currents; explain why the no-excitation resting voltage stays unchanged.

5. Discriminate a changed mechanism

Apply the mechanism to a changed boundary

At excitation 0 and shunt 3, find voltage and depolarization. Does conductance stay unchanged?

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

Compare a worked response

Voltage remains −60 mV and depolarization0, but total conductance rises to4. The unchanged baseline does not imply the shunt has no effect on responses to later input.

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.