Segmental actions of afferents of the interosseous nerve in the cat.

Electrical stimulation of the interosseous nerve evokes oligosynaptic inhibition of extensor motoneurones and excitation of flexor motoneurones. Lowest-threshold, shortest-latency post-synaptic potentials evoked at group I strength are attributed to the action of group Ib afferents. Post-synaptic potentials evoked at slightly higher stimulus strengths (within the higher group I and the group II range) and at longer latency are attributed to the action of afferents of Pacinian corpuscles. Facilitation of post-synaptic potentials evoked from afferents in the interosseous nerve by group I muscle afferents and by joint afferents is taken to indicate convergence of these afferents onto common interneurones in reflex pathways to motoneurones. Evidence is presented that afferents of Pacinian corpuscles project to the interneurones mediating group I (non-reciprocal) reflex actions to motoneurones. Unitary monosynaptic excitatory post-synaptic potentials (e.p.s.p.s) evoked from the interosseous nerve are taken to indicate that only a very small number of muscle spindle Ia afferents course through the interosseous nerve. Dorsal root potentials evoked by low-strength electrical stimulation of the interosseous nerve are largely attributable to the action of afferents of Pacinian corpuscles.