FACIAL INPUT TO NECK MOTONEURONS - TRIGEMINO-CERVICAL REFLEXES IN THECONSCIOUS AND ANESTHETIZED CAT

Cutaneous facial inputs influencing head movement were examined in the conscious and anaesthetised cat. EMG recordings were made in neck mus cles of conscious, unrestrained cats in which an unexpected light cuta neous stimulus was applied to the glabrous skin of the planum nasale ( PN). These observations established that head aversion movements were associated with synchronised activation of both deep and superficial d orsal neck muscles. In anaesthetised cats in which activity in the mot oneurons of the large dorsal neck muscles was examined, mechanical sti mulation of the PN or electrical stimulation of the infraorbital nerve (ION) produced a short latency, reflex activation. The reflex could b e elicited by excitation of low threshold, rapidly conducting fibres i n the ION. Intracellular recording from neck motoneurons showed that t here is a short latency, probably disynaptic, excitatory pathway from low threshold nerves in the ION to neck motoneurons, but discharge of neck motoneurons occurred several milliseconds later, presumably as a result of activity in a longer multisynaptic pathway.