Magnesium-block factor

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For nonnegative magnesium concentration, the denominator is at least one and the factor lies between zero and one. Increasing voltage reduces the exponential term and increases the unblocked fraction. The coefficients assume the voltage and concentration units stated in the source.

Terms & definitions

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Original context

    void step(float dt) {
        s *= std::exp(-dt / tau);
    }
};

// NMDA Receptor (slow excitatory, voltage-dependent Mg2+ block)
// I_NMDA = g_NMDA * s * B(V) * (V - E_NMDA)
// B(V) = 1 / (1 + [Mg2+]_o * exp(-0.062*V) / 3.57)
struct NMDASynapse {
    float g_max = 0.5f;      // nS
    float E_rev = 0.0f;      // mV
    float tau_rise = 2.0f;   // ms
    float tau_decay = 100.0f;// ms - NMDA is slow!
    float Mg_o = 1.0f;       // mM - External Mg2+ concentration
    float s = 0.0f;
    float x = 0.0f;          // Rise variable

    // Mg2+ block factor

B(V) = 1 / (1 + [Mg2+]_o * exp(-0.062*V) / 3.57)

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