CONNECTIONS BETWEEN UTRICULAR NERVE AND NECK FLEXOR MOTONEURONS OF DECEREBRATE CATS

We studied the circuitry between the utricular CUT) nerve and ventral neck motoneurons innervating the longus capitis (LC), a neck flexor mu scle, in decerebrate cats. We recorded intracellularly from 63 LC (ips ilateral 37, contralateral 26) motoneurons in C1 and C2 segments. UT n erve stimulation evoked disynaptic, excitatory postsynaptic potentials in all ipsilateral LC motoneurons, and inhibitory postsynaptic potent ials that were at least trisynaptic in almost all contralateral LC mot oneurons. UT effects on neck motoneurons innervating muscles involved in flexion and lateral turning are similar to the connections between the UT nerve and neck extensor motoneurons. These neuron circuits may play a role in fixing the head and the neck to the body during horizon tal linear acceleration.