Squid giant axon

The squid giant axon is the very large (up to 1.5 mm in diameter; typically around 0.5 mm)

On the underside of the squid's body, between the head and the mantle, is a siphon through which water can be rapidly expelled by the fast contractions of the body wall muscles of the animal. This contraction is initiated by action potentials in the giant axon. Action potentials travel faster in a larger axon than a smaller one,^[5] and squid have evolved the giant axon to improve the speed of their escape response. The increased radius of the squid axon decreases the internal resistance of the axon, as resistance is inversely proportional to the cross sectional area of the object. This increases the space constant ($\lambda ={\sqrt {(r\times \rho _{m})/(2\times \rho _{i})}}$), leading to faster local depolarization and a faster action potential conduction ($E=E_{o}e^{-x/\lambda }$).^[6]

In their

• Lateral giant neuron
• Squid giant synapse
• Hodgkin–Huxley model

References