Input patterns and pathways from the six semicircular canals to motoneurons of neck muscles. I. The multifidus muscle group

1. The pattern of connections between the six semicircular canals and neck motoneurons of the multifidus muscle group was investigated by recording intracellular potentials from motoneurons in the upper cervical cord of anesthetized cats. 2. Synaptic potentials were recorded in motoneurons of the rectus capitis posterior (RCP) muscle at C1, the obliquus capitis inferior (OCI) muscle at C1 and C2, and the cervical multifidus muscle (Multi) at C4 in response to electrical stimulation of individual ampullary nerves of the six semicircular canals. Excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs, respectively) were evoked by separate stimulation of individual ampullary nerves in all of the neck motoneurons. Virtually all of the neck motoneurons received convergent inputs from the six ampullary nerves. 3. Motoneurons that supplied a single muscle had a homogeneous pattern of input from the six semicircular canals. There were two patterns of input from the six semicircular canals to motoneurons ...