Elements of Nervous system br 1. Neurons br The chief structural and functional units of the Nervous system are Neurons. br Neuroglia br Types of Neurons. br 1. The Sensory Neurons. br 2. Associative Neurons. br 3. Motor Neurons. br Nervous system of flatworm br Receptors br Nerves and Nerve Plexus br Receptors types of Planarian br Coordination and Control br Chapter No.