This illustration demonstrates the contraction of the squid mantle in response to the simultaneous activation of muscle throughout the mantle by the axons.

Steps in this sequence

1. Squid at rest.
2. Mantle opens. Water enters the mantle cavity.
3. A signal from the brain (cerebral ganglia) is sent to the stellate ganglion. The stellate ganglion is in turn connected to nerve cells (axons) distributed throughout the mantle.
4. Nerve impulses travel the length of these axons. The longer the distance the thicker the axon. Thicker axons allow for faster conduction because there is less internal resistance in a wide-bore axon. Thus, the impulse reaches the muscles throughout the mantle simultaneously.
5. The result is that the muscles contract synchronously, rapidly closing the mantle, and forcing water out of the mantle cavity
6. Water is expelled through the siphon, producing a jet action. By controlling the direction of the siphon the squid can make rapid direction changes.

Adelman, William J., Gilbert, Daniel, L., Electrophysiology and Biophysics of the Squid Giant Axon, From Squid as Experimental Animals, Plenum Press