Two Inhibitory Fibres forming Synapses with a Single Nerve Cell in the Lobster

Abstract

IN the stretch receptors of lobsters described by Alexandrawicz¹ the dendrites of sensory neurons lie in a fine muscle strand. Stretch-deformation by passive pull or by contraction of the receptor muscle leads to depolarization of the dendrites and of the adjacent cell body and axon region, thus setting up sensory discharges. In most lobster receptors Alexandrowicz also found two efferent neurons, a thick and thin ‘accessory’ fibre, forming synapses in the dendritic region of the sensory cells. Both accessory fibres divide and send one branch to the slowly adapting neuron and the other to the fast adapting receptor cell (Fig. 1). It has already been shown that stimulation of the thick accessory fibre can promptly suppress the sensory discharge caused by stretch of the muscle strand². This axon therefore has a specific inhibitory role.