Axona

Axona's squid armour carries a tentacle axon, and when she fires, a spike of light travels down it.

The Physics

Hodgkin and Huxley explained the nerve impulse of the squid giant axon with a circuit: the membrane's capacitance in parallel with sodium, potassium and leak conductances. Sodium channels open fast and close more slowly; potassium opens with a delay. Their equations reproduced the shape of the action potential and its speed.

C_m dV/dt = −ḡ_Na m³h (V − E_Na) − ḡ_K n⁴ (V − E_K) − g_L (V − E_L) + I

• C_m: membrane capacitance (F)
• V: membrane voltage (V)
• t: time (s)
• ḡ_Na, ḡ_K, g_L: maximum sodium, potassium and leak conductances (S)
• m, h, n: gating variables (dimensionless, 0–1)
• E_Na, E_K, E_L: reversal potentials (V)
• I: applied current (A)

A. L. Hodgkin and A. F. Huxley published it in 1952; it predicted a conduction speed of 18.8 m/s against 21.2 m/s measured.

Honest caveat: The tee uses the modern voltage convention (rest ≈ −65 mV, peak ≈ +40 mV), not the 1952 paper's original sign convention.

On the shirt

Front: Axona, the pixel-art character, with the title. Back: the membrane equation, the gating equation, the speed prediction, the modern convention note and the 1952 paper. Printed on a unisex tee.