Accurate simulations of peripheral nerve recordings are needed to develop improved neuroprostheses. Previous models of peripheral nerves contained simplifications whose effects have not been tested. We have created an anatomically detailed finite element model of a rat sciatic nerve using MRI imaging, and used it to carry out a sensitivity analysis of relevant parameters. We simulated neural recordings from a multicontact nerve cuff electrode and validated them with in vivo experimental data. We found that varying tissue conductivities had little influence on the simulated recording selectivity of the cuff, as we found high correlations between in vivo and simulated measurements for a wide range of conductivity values. On the other hand, the increased anatomical detail did substantially alter the recording patterns observed. It can be concluded that our model is an improved simulation tool and can be used in the design of neural interfaces.