We demonstrate non-contact sub-nanometer optical measurement of neural surface displacement associated with action potential propagation. Experimental results are recorded from nerve bundles dissected from crayfish walking leg using a phase-sensitive optical low coherence reflectometer. No exogenous chemicals or reflection coatings are applied. Transient neural surface displacement is less than 1 nm in amplitude, 1 ms in duration and is coincident with action potential arrival to the optical measurement site. Because the technique uses back-reflected light, noninvasive detection of various neuropathies may be possible.