Nerve impulses control muscle contractions, therefore, insecticide poisoning of nerve functions is often observed as erratic muscular activity. In the following animation, we will examine how the nerves control the muscles, and what happens when an insecticide poisons a nerve or muscle. If we look at our internal cutaway of an insect, we will show how a nerve impulse causes the leg to move. In this view of the interior of a ganglion, we see the axon of an input neuron that brings behavioral information into the ganglion from somewhere in the central nervous system. The information is transferred from the input neuron to a ganglionic neuron at a synapse. The ganglionic neuron transmits the information further at its synapse with a motor neuron which sends nerve impulses to the muscles of the jumping leg. When the nerve impulses reach the leg muscle, they spread over the surface of the muscle and stimulate the leg muscle to contract. If the nerve impulses are conveyed correctly, they cause the leg muscles to contract in a controlled manner for normal walking. However, when an insect has been exposed to many of the commonly used insecticides, the nervous system is poisoned and the neurons fire erratically and continuously. The continuous erratic nerve impulses cause the leg muscles to be stimulated constantly — producing uncontrolled erratic twitches instead of smooth controlled contractions. We will now examine how specific insecticides exert their toxic actions and disrupt nervous system function.