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 Squid at rest.
Water enters the mantle cavity.
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. The result is that the muscles contract synchronously, rapidly closing the mantle, and forcing water out of the mantle cavity Water is expelled through the siphon, producing a jet action.