Conduction of excitation in spinal reflex arcs in cat fetuses

Abstract

The electrophysiological characteristics of conduction of excitation in afferent and efferent components of reflex arcs were studied in cat fetuses during the last three weeks of prenatal development. The placental circulation was maintained during the experiments. In embryos investigated 23–17 days before birth, reflex responses arising in motor nerves to stimulation of dorsal roots consist of one well-synchronized component. In the later stages of fetal development reflex responses consist of two components reflecting conduction of excitation along monosynaptic and polysynaptic reflex arcs. The central reflex time in the fetuses studied is 1.5–2.3 msec. The velocity of conduction of excitation along afferent and efferent nerve fibers varies from 1.5 to 8 m/sec. Most nerve fibers conduct excitation at 4–5 m/sec. High amplitude of the P-wave of the dorsal surface potential and the dorsal-root reflexes which are constantly observed in them give evidence of strong depolarization of afferent fiber endings in the fetuses.