Rapid pressure changes and surface displacements in the squid giant axon associated with production of action potentials.

By using both optical and mechano-electric detectors, we have shown that the squid giant axon swells when an action potential is generated. The maximum swelling is reached at the peak of the action potential. The undershoot of the membrane potential is associated with a marked shrinkage of the axon. We have also demonstrated these mechanical changes in axons from which a major portion of the axoplasm has been removed. We have examined the effects of changing the tonicity of the external medium and of applying several chemical reagents.