Changes in light scattering associated with the action potential in crab nerves.

1. Changes in light scattering from stimulated crab leg nerves were measured in an effort to study changes in structure that occur during the action potential.2. The peak changes in scattering after individual stimuli were 10(-4)-10(-5) of the resting scattering; signal averaging techniques were used to increase the signal-to-noise ratio.3. During the compound action potential there was a transient increase in the 90 degrees scattering which reached a peak about 20 msec after the stimulus. This increase was probably not due to a change in axon volume. Its time course was somewhat slower than that of birefringence changes measured at the same time.4. In normal sea water the transient increase was followed by a longer lasting (persistent) decrease in scattering. This persistent decrease could be converted to an increase by reducing the tonicity of the sea water or by raising the external refractive index. This scattering change may represent a swelling of the axon resulting from the ionic exchanges that occur during the action potential.