NERVE IMPULSE, DRAWING. NERVE IMPULSE, DRAWING Illustration of the transmission of a nerve impulse with a central close-up showing how the transmission occurs between a synapse on neuron A to a dendritic spine on neuron B. Vesicles liberate excitatory neurotransmitters (purple triangles) which open the sodium channels and enable Na+ ions (red spheres) to penetrate a dendritic spine on neuron B, creating an electric current which travels along the latter neuron´s axon to its synapses.