Pyramidal Effects on Lumbo‐Sacral Internewones Activated by Somatic Afferents

Intracellular recording was made from 23 interneurones in the dorsal horn and intermediate region. Stimulation of the sensorimotor cortex evoked excitatory postsynaptic potentials in interneurones receiving excitatory action from: 1) group I muscle afferents, 2) flexor reflex afferents, 3) cutaneous afferents. In a few of the interneurones the latency was so brief as to suggest a monosynaptic connexion from the pyramidal tract. Stimulation of the sensorimotor cortex evoked inhibitory action only in one interneurone, which received inhibitory action from the periphery as well. The findings are discussed mainly in relation to facilitatory actions evoked by volleys in the pyramidal tract on paths from primary afferents to motoneurones.