A device for detecting impulses within a nerve comprises (i) a support (21, Fig 2) for securing to the epineurium of the nerve (for example a nerve cuff of flexible material wrapped around the nerve), (ii) at least one spike 22, 23 extending from said support, arranged to penetrate the perineurium and (iii) at least one chemical sensor (27, Fig 4) arranged on a surface of the at least one spike. The spike may also carry an electrical signal for stimulating at least part of the nerve. The chemical sensor may be sensitive to at least one of K+, Na+, Cl- and H+.
