Multisensory Control of Spinal Reflex Pathways

Abstract

This chapter reviews the convergence from different primary afferents on interneurones in reflex pathways. It summarizes results showing that interneurones of the reciprocal Ia inhibitory pathway receive a wide convergence resembling that found in agonist motoneurones. Interneurones in reflex pathways from Ib afferents are excited from cutaneous and joint afferents and also from Ia afferents. The chapter describes reflexes from the FRA (flexor reflex afferents)—that is, reflex actions from high threshold muscle afferents, joint afferents and cutaneous afferents that are mediated by common interneurones. A distinction is made between short-latency reflexes in the acute spinal and long-latency reflexes in acute spinal cats after DOPA i.v.; the half-centre organisation of the interneuronal network mediating the latter reflexes is recapitulated and discussed in relation to spinal generation of alternating activity in flexors and extensors. An important role of reflex pathways from the FRA in motor control is indicated by findings showing that their interneurones are excited from different higher motor centres and that many ascending pathways, spinocerebellar in particular, signal information regarding their interneuronal activity.