Intramuscular localization of monosynaptic Ia reflex effects in the cat biceps femoris muscle.

Intracellular recordings form biceps femoris (BF) motoneurons were made in anesthetized low spinal cats during periods of electrical stimulation of the nerve branches supplying the anterior, middle and posterior portions of the BF muscle and the nerves to semimembranosus and semitendinosus. Measurements were made of each cell's composite intrahomonymous and heteronymous monosynaptic Ia-EPSP responses to stimulation of the test nerves (branches). We have found evidence for an intramuscular localization of these monosynaptic Ia reflex effects not only when comparing responses between the two functional components of the BF muscle as is well established [6] but, in addition, when comparing responses between different parts of each functional (hip extensor and knee flexor) component as well. It is argued that both somatotopic and neuronal recognition factors may contribute to the localization of these monosynaptic reflex effects.